>> Roland Fernandez: Hi. I'm Roland Fernandez from... great pleasure to introduce Kate Possin from UCSF Memory and...

>> Roland Fernandez: Hi. I'm Roland Fernandez from Microsoft Research. It's my
great pleasure to introduce Kate Possin from UCSF Memory and Aging Center. She's
going to talk to us about her current work.
>> Kate Possin: Thank you, Roland, and thank you for having me here. It's been a real
honor to, first of all, just get to collaborate with your group, some research and
navigation. And it's an honor, too, to be able to come here and see what you all do
firsthand. So thank you very much for having me.
I'm used to giving talks to neuroscientists. So please feel free to ask me questions if what
I'm saying is not clear, if I'm making assumptions about things that you may already
know or you don't know.
So I'm going to be talking about visuospatial cognition in neurodegenerative diseases
today. And this is an area that I've been working on with Roland and Desney. We've
been developing some new virtual reality tests of navigation.
I come from the Memory and Aging Center at UCSF where we do provide a lot of
clinical care, but we're very much involved in research. And we're trying to develop
better methods to diagnose neurodegenerative diseases, like Alzheimer's disease. And we
want to find ways to diagnose them in their earliest stages so that as treatments become
available we'll be able to help patients as early as possible.
We at need measures that can track progression of disease so that we can measure
whether or not these new treatments are working.
We're also, a lot of people in our group, working on finding the actual cures for these
diseases. So our research is twofold. I'm more involved with the first aim in developing
these methods for diagnosis and measuring progression.
I'm going to start out by giving some background on how to test visuospatial cognition by
thinking about anatomy, and then I'm going to talk about how I think visual cognition is
organized in the brain according to three primary schemes: dorsal and ventral, top-down
and bottom-up, and lastly egocentric and allocentric, which is the focus of the work I've
been doing with Microsoft.
And lastly I'm going to think about with you how visuospatial cognition is disrupted in
different neurodegenerative diseases. And I've decided to focus on the three most
common kind of neurodegenerative diseases.
So Alzheimer's we see as being the most common; and then Parkinson's disease, which in
80 percent of cases is associated with dementia before death; and frontotemporal lobar
degeneration, which you may not have heard of. It's -- people are really only beginning
to understand that disorder in the last ten years or so. It's an earlier onset kind of
dementia. Typically hits people in their 50s or 60s.
When a neuropsychologist like myself does an evaluation to see if someone might have
an neurodegenerative disease, I focus on four primary areas of cognition: memory,
language, executive functioning, and visuospatial skills.
I think this last domain is perhaps the least well studied and evaluated in dementia
evaluations. And perhaps that's was it's hard to measure with paper-and-pencil tests. It's
hard, for example, to figure out if someone can navigate through a new environment by
asking them to copy a figure on a piece of paper.
Now, with technology that your group is working on here, we have the ability to test
visuospatial skills in an ecologically valid way by immersing patients in a new world and
see how well they can navigate through it. So I think these new advances in technology
are offering a potential pathway down which neuropsychologists can do a much better
job of evaluating visuospatial skills.
Well, why do we evaluate all this cognition? The reason is is that the types of cognitive
problems that a person has depends on where the pathology is in the brain. For example,
if you have damage to your hippocampus in your medial temporal lobe, you're going to
have trouble with memory because that part of the brain is essential for laying down new
Alzheimer's patients, this is the first area of the brain that is hit. And that's why
Alzheimer's patients typically have memory loss as their first symptom. By examining
the pattern of cognitive strengths and weaknesses that a patient has, I can get a sense of
which parts of their brain are working and which parts of their brain are not working.
This is important because different diseases have characteristic ways that they impact the
brain. So Alzheimer's tends to start in the hippocampus and surrounding areas and then
move into temporal and parietal cortex. Whereas frontotemporal dementia tends to start
in the front part of the brain, the frontal lobes. And that part of the brain is pretty well
preserved. So these different diseases have their own signatures of how they start and
how they progress.
A good test, there for, is going to be specific to the anatomic and cognitive mechanisms
of the diseases that you're studying. So a good test needs to be anatomically specific. If
a patient can fail a test because of damage to the front of their brain or their back of the
brain, that's not going to help us distinguish between Alzheimer's and frontotemporal
So just as an example of these patterns of pathology, this is a study of the atrophy, where
the atrophy is in the average Alzheimer's patient, on the left here compared to controls,
and then frontotemporal lobar degeneration.
So in Alzheimer's disease you see there's this damage in the back of the brain that's
getting atrophied. The front is relatively well preserved. You can't see that medial
temporal lobe hippocampal area here, but it's inside here. And then frontotemporal
dementia has more problems in the front of the brain collapsed across many subjects.
So a good test to distinguish between these diseases would separately measure the
functioning of those frontal or posterior brain regions.
As I mentioned, visuospatial cognition is in the Dark Ages in terms of how we're
assessing it these days in clinic. Pretty much everyone who assesses visuospatial
cognition in a dementia evaluation is going to show a patient a figure like this one and
ask them to copy it.
However, a patient can fail this for many different reasons. Perhaps they have trouble
simply perceiving aspects of the figure, perhaps they can't organize it in their mind or
come up with a good plan for how to go about copying it, or maybe they have motor
So there's a study I'm writing up right now where I examine the performance of patients
on this test, and the patients either have a diagnosis of Alzheimer's disease or
frontotemporal dementia. So those diseases I just showed you in the last slide.
So both patients have trouble with this test but for different anatomical reasons. So in
Alzheimer's disease, having trouble on this test was associated with atrophy in the right
parietal lobe. That's right here. That's the part of the brain we traditionally think of when
we think about visuospatial processing. Where the right frontal lobe, however, was not
involved with performance in these patients.
We see a different -- yeah. Please.
>> What's the nature of the atrophy when you say atrophy? Is it neuron death or is it sort
of like water atrophy? Or, I mean, is it well understood?
>> Kate Possin: Well, we operationalize it here by just there being less gray matter in the
brain. So we assume that means that there has been cell death that has led to decreased
volume in that brain area.
>> So you perceive it as less activity, right, when you measure the images?
>> Kate Possin: Well, here we're not measuring activity per se, but we might if we were
doing functional MRI, and which is I think an also really interesting way to look at this.
In the behavioral variant FTD patients who have that atrophy in the front of their brain,
they are failing it for two different reasons, really. Yes, parietal lobe still correlates.
Right parietal lobe is just such a critical visual/spatial region. But they also can fail it
because they're having atrophy in their right frontal lobe.
So there's this -- these different neural mechanisms underlying their difficulties on this
>> Can I ask another question?
>> Kate Possin: Yes, please.
>> Are you using right as an example or is it really that asymmetric?
>> Kate Possin: That's a great question. Visuospatial processing is processed much
more by the right side of our brain than the left. Language, on the other hand, is on the
left side of the brain, which is why we're focusing on the right here.
>> This patient showed degeneration of the left side also, but it's more severe and more
consequential on the right?
>> Kate Possin: In terms of visuospatial skills, if I was looking at the correlates of
performance on a language test, we would see the left side of the brain playing a bigger
role. But, yeah, the diseases usually tend to start for an individual patient on one side or
the other and then spread to both sides.
Also looked in the same sample at the cognitive mechanisms, just correlating
performance on that figure copy with performance on other tests.
So spatial perception, just being able to perceive where locations are in space, was highly
associated in Alzheimer's disease patients with performance on that test, but was not
associated in the FTD patients. Instead, for them performance was associated with
performance on a test of spatial planning or problem solving, these sort of executive
higher-order aspects of spatial cognition that the front part of the brain is so important
So, in conclusion, this test of figure copy, which is how pretty much everybody assesses
visuospatial cognition right now as a neuropsychologist, can be failed for different
reasons and is not very useful for separating these two common causes of dementia. Yes.
>> If they're failing at spatial perception, are they having motor control issues, too, or
[inaudible] damage in the motor cortex as well?
>> Kate Possin: That's a good question. I guess it depends on where the perceptual
problems are coming from. But, you know, if you're having perceptual problems because
of parietal atrophy, your motor functioning might be fine. You might have trouble, you
know -- if I'm trying to reach for this bottle, I might kind of miss it, but their motor
function isn't too bad. If it's coming from more of a subcortical origin, then the motor
system is often impacted.
>> It seems like, though, eventually that would cause problems, because you'd be
>> Kate Possin: If it's severe enough, absolutely, these patients have a lot of trouble
getting through the environment. Absolutely.
So we finished the first part, the background of the talk, and now I'm going to move into
how is visual cognition processed by the brain using these three schemes.
A little background. So visual information enters the brain through the eye and travels
through axons of ganglion cells to this optic chiasm. So visual information on the right
side of your visual world but seen by both eyes is going to actually go to the left side of
your brain, and information on the left side of your visual world is all going to go to the
right side of your brain, so that that cross happens here. And then the information goes
through the thalamus and through all these axons to primary visual cortex in the back of
your brain. So that's where all the visual information goes first in the cortex.
If you have a lesion anywhere in that system, you're going to have a blind spot. There's
going to be part of your visual field that's completely missing.
As the information leaves primary visual cortex, more complex aspects of the visual
world are processed and separated. So there are regions that are important for processing
motion and color and form and depth. So these are all processed by different areas. So if
you have a lesion on any of those areas, you're going to -- you're not going to have a
blind spot, but you're going to be impaired at processing some aspect of the visual world.
Information moves anteriorly through the brain in these dorsal and ventral streams. The
dorsal stream is also called the where stream. It processes where things are in space.
And this goes through the parietal lobe. It's also been called the how stream because we
encode the locations of objects based on how we would act on them.
For example, I'm encoding where this bottle is maybe in terms of how I would reach out
and grab it. So this is very tied with the motor system, which is the point that you made.
The ventral stream here goes through temporal cortex. This is the what stream. It
processes the features of objects that are relevant to their identity, like color and form.
So it's interesting that these are separated, the what and the where, but if you think about
it in the real world, what this bottle looks like has nothing to do with where it's sitting.
And if I move it over here, it still looks like the same bottle. So our brains represent this
functional real-world distinction, I think.
So I think this is an important scheme, and we definitely see patients in clinic all the time
that have damage more to the dorsal where stream or to the ventral what stream.
I'll show you some examples of how we test these constructs. So this is a test of dorsal
stream processing. This is you have to say which number up here is in the same position
as this dot. So which number is it?
>> Seven.
>> Kate Possin: Seven. All right. You guys passed. Good. It's a real easy test for
controls. And this is a test of object recognition. So you have to say which one is a
silhouette of a real object. I kind of chose a pretty easy example. I think you guys can all
see that that's a stroller.
The next distinction I'm going to talk about is top-down and bottom-up processing.
Progressively more complex aspects of the visual world are processed as representations
moved from the back of the brain forward.
Top-down processing, on the other hand, is conducted by the front part of your brain,
your frontal lobes and these circuits that connect the frontal lobes to subcortical regions.
So this anterior brain selects representations in posterior cortex that are in need of further
processing, like I want to pay more attention to that object in the environment. Also
helps you manipulate those representations in your mind, inhibit irrelevant information,
maintain those representations in your very short-term memory after this stimuli are no
longer available in your environment. So these executive aspects of visual processing.
So this distinction, as you can imagine, is important for the diseases I just mentioned.
Often frontotemporal dementia patients have more trouble with the top-down and
Alzheimer's more with the bottom-up, for example.
The last distinction is that of egocentric and allocentric frames of reference. In the
egocentric system we're representing the locations of objects in the environment relative
to our own position. And we continuously update that information as we move through
the environment.
So this is important both in very short-term representations, like your working memory.
If you're moving through a crowded room and trying to find a place to sit down, you're
encoding where all these objects and people are relative to yourself and continuously
updating them to guide your movement. So this system is very tied with the motor
The caudate nucleus, which is a subcortical structure in the brain, deep in the gray matter
of your brain in the basal ganglia, that brain region has been shown to really anchor this
egocentric network in rodents. And I think also in humans. Parietal cortex is also critical
for this egocentric frame of reference.
This system is important also for habit or routine learning. So when you've taken the
same route so many times that it just becomes a routine, you're using the system. You
don't even feel like you have to think about it anymore. You take the same route every
day to work. Maybe one time you're planning to go to the store instead, but you forget to
turn off to go to the store because you're so used to going to work every day. That's
that -- that's the egocentric system.
The allocentric system, on the other hand, represents the locations of objects in the
environment, particularly boundary cues and major landmarks relative to each other.
And they form a cognitive map, if you will.
For example, let's say you wanted to go to the store after work. You've never been to that
store from work before, you've only been there from home. And you know the store is
west of home and home is north of work, so then you know you need to go northwest to
get to the store. You've created this 3D representation of where these landmarks are for
you, and you can manipulate yourself in those landmarks.
So this is important for developing these cognitive maps of the environment that are
independent of your own position in the environment. If someone plopped you down in
Seattle in some other place, like you'd be able to figure out where you were relative to
some major buildings or the direction of the sun and you could probably get a general
sense of which way you needed to go home.
Taxi drivers use this system all the time. They can't take the same route all the time.
They have to continuously find the most efficient route to get somewhere and maybe that
they have never been to before from that place. So they're using these cognitive maps
more than probably anyone else.
And there was some really interesting research out of London that showed that taxi
drivers indeed have larger hippocampi, so that's the structure in the brain that's really
anchoring this system. And in fact years of experience as a taxi driver was correlated
with bigger hippocampi.
Some people have suggested perhaps that if we practice using this system we can make
our hippocampi more robust to the effects of aging and Alzheimer's disease, where the
disease first starts.
So I'm working on it. My -- actually, women tend not to be as good as using this system
as men. But I'm hoping practice will help.
>> How do you practice?
>> Kate Possin: How do you practice?
>> Yeah.
>> Kate Possin: Well, don't use MapQuest all the time. Yeah. Instead maybe study a
map and try to get a sense of where things are relative to each other.
>> I also heard that playing soccer helps.
>> Kate Possin: Playing -- how come?
>> Just [inaudible].
>> Kate Possin: As long as you don't get hit in the head I think it helps.
>> Going to start blindfolding my kids and dumping them in random locations.
>> Kate Possin: The reason we know so much about this egocentric and allocentric
frames of reference is that they've been studied extensively in rodents.
When you want to measure rodent cognition, what people do is they measure forms of
navigation. This is the most popular test of navigation in the rodent. It's the Morris water
The rodent is plopped down in this cold pool of milky water that has a hidden platform
and they swim around desperately trying to find a way to get out until they find the
platform. And then the rodent is placed back in the pool from a different starting
position. The rodent then swims around again trying to find the platform.
So this is repeated over and over again. The rodent gets better at finding the platform.
And by manipulating things, like the types of cues available, you can test different forms
of navigation.
For example, if you have the rodent start from a different starting place in every trial,
they can't just memorize a route to get to the platform. Instead they have to memorize the
relationship of the platform to the boundary cues. For example, the things around the
pool, maybe it's the door and the computer and the things that are in your laboratory
around. So he learns -- he creates a map of the platform relative to those cues, and he can
use that to find the hidden platform.
Another version of the test, they rotate the pool on every trial so those cues on the outside
aren't helpful, and they start the rodent from the same position in the pool relative to the
platform. And so then they just learn the route over and over again.
So you can see the first one I described tests more of the allocentric cognitive map
building, hippocampal dependent kind of navigation, and the latter one was testing that
caudate nucleus-dependent route learning egocentric form.
So when we're trying to find cures for neurodegenerative diseases, we test them in rodent
models of dementia first. So the idea of having a navigation test that was analogous to
the ways that we're measuring cognition in rodents for our human patients is very
Because if we see that a drug for Mouseheimer's, which is the mouse version of
Alzheimer's, works because the rodents are doing better on the Morris water maze, well,
why don't we have a human version of the Morris water maze to see if the drug works in
humans. So it's nice to be able to translate these findings back and forth.
I'm going to briefly present this study. This is a virtual navigation study that was done in
young adults, young, healthy adults. And this is a radial maze. So there are eight of
these paths that someone could take off the center. And in half of them there is a treasure
that they have to find.
The first time they go through the ones without a treasure are blocked and they're just
supposed to remember which ones do have a treasure, and then the next time they go
through they go and look for the treasure. The treasures are like down at the end and
they're kind of hidden.
So the subjects have to learn which of the -- which four of the eight arms have the
treasure. Well, there are these mountains or a sunset, depending on which way you're
looking, and you can use those boundary landmark cues to help you, or you can kind of
remember that, oh, yeah, there's two next to each other, and then I keep going, I pass one
and I get to another one. More of a route form of finding the treasure.
So there's two different strategies which are arguably more of an allocentric and then an
egocentric strategy. You could use either one.
So what the researchers did was they -- after they performed the test, the subjects
performed the test, they removed these boundary cues, so it went black, and then saw
how the people did. And the idea was the people who hadn't built that cognitive map,
they didn't use those external cues, they were still going to do fine. But the people who
had been relying on them, they had built a cognitive map, were now going to fail. And
then they correlated the number of errors with gray matter in the brain.
And they showed that the people who made a lot of errors actually had bigger
hippocampi. So that suggests -- which is the area for building cognitive maps. So they
argued that, well, these people were building cognitive maps, they weren't using the other
strategy, and so that's why they then failed when we took away the boundary cues.
In contrast, the people who made fewer errors on the probe had a bigger caudate nucleus.
So that's the structure that's important for that route learning egocentric, and they were
able to do -- they were using that strategy and so they made fewer errors at the probe.
So that's one of the virtual reality tests that has been used out there. And I've been
working on some other ones I'll show you shortly with Roland.
So we went over those schemes of visuospatial cognitions. So just to review, dorsal
ventral is where processing versus what processing. There's that top-down, bottom-up
distinction, depending on top-down executive control and bottom-up early visual
processing. And then we just talked about the egocentric, allocentric distinction.
I think these schemes can be helpful for us to understand how visuospatial cognition is
disrupted in neurodegenerative diseases.
I want to start with Alzheimer's which is of course the most common cause of
neurodegenerative disease. Actually, before I do, I'm realizing I should back up a little
bit and tell you why are there different neurodegenerative diseases.
Well, each of these diseases is associated with aggregations of a different type of protein
in the brain. So if we cut open a patient's brain who has Alzheimer's, we're going to see
these amyloid plaques and we're going to see these neurofibrillary tangles in their brains,
so these signature types of pathology that we think are probably causing the disease. If
we open someone's brain with Parkinson's disease, we're going to see aggregations of
alpha synuclein protein.
So these are different diseases at a pathological level. And the reason that we need to be
good at diagnosing these diseases is because the treatments for each of these diseases are
going to be different. The treatments that we're evaluating right now are designed to
target and clear or prevent the build up of these abnormal proteins.
So Alzheimer's disease, these patients have quite a bit of visuospatial dysfunction. This
is a patient with a mild level of dementia. There is a global test of cognition that most
doctors use called the mini-mental state exam. This patient had a score of 20 on that test.
And you can see that there's some spatial distortions and misplacements in this figure.
These patients have diffusely decreased cortical gray matter, most -- really prominent in
the posterior temporal and parietal regions.
So I showed you the dorsal ventral streams. These patients have trouble with both the
dorsal and the ventral stream. They typically have more trouble with this bottom-up
processing, whereas the top-down executive aspects in most cases are relatively spared.
Certainly there's a lot of variability, however. Some patients, they have a more frontal
In this study, patients who were diagnosed with mild cognitive impairment who were
thought to have a very, very early form of Alzheimer's disease were followed. And the
patients who went on to develop Alzheimer's disease a year later, this is what their -- this
is where they had atrophy in their brain. It was located just in this medial temporal lobe
region. And that's where the hippocampus is.
So in these patients who didn't have Alzheimer's yet but were about to get it, their atrophy
was circumscribed to this region. At the time of diagnosis a year later, we see quite a bit
more atrophy, all those red areas involving the temporal and parietal cortex, and a little
bit in frontal cortex. So a bit more diffuse, but still following a characteristic pattern.
So this clearly tells us if we want to identify patients in the early stages, we need tests
that are going to really measure the functioning of that region. Yeah.
>> Going back two slides, it looks like the atrophy is lateralized as well towards the right
region. Is that true? Or is that just the characteristic of the two slides?
>> Kate Possin: Well, and also sometimes it depends on just your sample. I don't -- I
can't say that Alzheimer's more often affects the right or the left side. Sometimes you see
these differences in these studies. So let's see. There do seem -- like here it seems to be a
little bit more on the left than the right there.
>> [inaudible] to the right [inaudible].
>> Kate Possin: Sorry?
>> That previous one looked more on the right [inaudible].
>> Kate Possin: Oh, yeah. I think it's just a function of your sample and some
variability. I don't think people generally think that this disease on average starts on one
side or the other. Other diseases, that's not always true.
So, anyhow, if you want to catch patients early with Alzheimer's, you want to test the
functioning of the medial temporal lobe, the hippocampus.
And because of that, I think allocentric navigation might be a really good way to get at
this. After all, in the rodent models of navigation, we know that the hippocampus
anchors that allocentric network.
So I'm thinking one thing that we're going to test out with the test that we're developing is
seeing if early Alzheimer's patients are selectively impaired at allocentric navigation.
And this a version of the task -- one of the tasks that Roland and I have been working on
that we think will measure allocentric navigation.
In this test, the patient is placed in a -- this circular field. They're not placed in a cold,
milky pool, like the rodents, but in a circular field. And they look around and try to find
a treasure. And because they start from a different position on every trial, they have to
find the treasure relative to the cues in the environment, those external boundary cues,
just like the rat had to find the hidden platform relative to the cues in the lab surrounding
the pool.
And we've actually just been working on this test this afternoon. And Roland's hooked it
up with this driving simulator which makes getting around in the environment really fun.
And we've been making the boundary cues quite a bit richer. And we'd love if anyone
wanted to stop by and try it out.
>> [inaudible] when you get within a certain [inaudible] of it? Is that right?
>> Yeah.
>> I'm sorry, maybe you're going to go into some more detail, but the metric is timed?
>> Kate Possin: Well, actually, that's something that we're probably working out today
and tomorrow. But some of the things we've thought about are time but also how much
ground is covered. Because I think some people might move faster. How much time is
spent in the quadrant where the treasure is located, like do they -- are they just randomly
looking all over, are they focusing their search. Those are some of the metrics that are
used with the rodents.
>> Is your goal to come up with a robust, quantitative metric or -- so the scenario you
talked about still had a therapist in the loop. Is it -- is it largely the goal to present a task
that just allows you to observe a different set of skills in the driving task where you just -if you look at the screen you would get at least a good sense of what somebody was up to
as a quantitative metric could produce? Is your goal that sort of therapist-in-the-loop
scenario, or to really produce a robust, quantitative estimation of where their skills are at?
>> Kate Possin: I definitely would like the latter, even if I was just working as a
clinician. I want a robust, quantitative metric. And, for example, if ten years from now
this is a clinical measure, maybe five, if this was a clinical measure, I want to be able to
compare my patient's performance to normative data.
So if I was going to validate this for clinical purposes, I'd probably run this on a thousand
controls, and then I could compare my patient's performance to how does a typical
healthy person do. So we definitely need, you know, the quantitative metric.
>> [inaudible] necessarily be supervised in every case, you wouldn't be staring at them
and doing qualitative evaluation of their strategies?
>> Kate Possin: Yeah, not necessarily. It would be great. I mean, I think that's one of
the advantages of these virtual techniques is perhaps the having the examiner there as
opposed to maybe just an assistant running the test is less important.
So as something we were talking about earlier today, this kind of having virtual tests of
cognition maybe can help neuropsychology reach into areas where neuropsychologists
are not available. Like many more rural places in the United States, for example, there
are no neuropsychologists. Maybe we can come up with a -- looking down the road, a
package virtual system for evaluating cognition and be able to help and diagnose more
Going to move on to the second of the three diseases now, Parkinson's disease.
Parkinson's disease starts in these areas in plaque, the brain stem and an olfactory tract,
and moves up the brain stem. It's not until stage 3 of the disease that the midbrain is hit
right here. And this part of the brain has the substantia nigra, which sends dopamine to
the basal ganglia, including the caudate nucleus, which I've been talking about quite a bit
The dopamine depletion in the basal ganglia is very severe. In fact, you need at least 80
percent depletion before you start showing any Parkinsonian symptoms.
The loss of dopamine is thought to cause the motor symptoms of Parkinson's disease and
also in the early state the early aspects of cognitive impairment. So patients with
Parkinson's disease do show subtle but meaningful impairments in cognition that affect
aspects of spatial and executive functioning.
And this is because the caudate nucleus is highly interconnected with the frontal and
parietal lobes. And these loops are important for these aspects of cognition. Losing the
dopamine hurts cognition because the dopamine is important for regulating the function
of those circuits.
So in some, you know, as the pathology moves up here to the midbrain, the patients are
going to start to show cognitive problems due to basal ganglia dysfunction as well as
motor dysfunction.
And this is the pathology that we're talking about. We see these aggregations of alpha
synuclein protein called Lewy bodies.
This is an image of some of these subcortical structures I've been talking about. This is
the caudate nucleus here, this rounded structure. And this is the putamen in here. The
putamen is very important motor function. The caudate is more important for cognitive
function and important for that egocentric navigation that we've been talking about.
So these are the projections for the substantia nigra, so these projections are lost in
Parkinson's disease, and so you don't get as much dopamine there. And so the circuits
that connect these structures with the frontal lobes in particular are impacted. So that
gives you a sense of why we see problems in Parkinson's disease. As the disease
progresses, more pathology moves into cortex.
Parkinson's patients have a lot more trouble with spatial information, location-based
information, than they do with object-based or verbal information.
This is an example of a working memory test, so very short-term memory. In one
condition of the test, the patients are told to pay attention to where these objects are
located on the computer screen. After a very brief delay, another object appears and the
subject has to say is that object in the same place as one of the two that you just saw or
not. So they're just maintaining spatial-based or location-based information.
A couple hours later they're given the test again, but this time they just have to pay
attention to what the objects look like, ignoring where they're located in space, is this the
same as either of the once you just saw.
Well, the Parkinson's patients have a select deficit in maintaining the spatial-based
information, that location-based information. And it emerges at a very short delay, at a
one-second delay, and doesn't worsen with increasing delays. So they have a select
problem with aspects of spatial attention in the earliest parts of working memory.
>> I just think of Parkinson's as a motor disorder. Do these more cognitive symptoms
actually appear around the same time as motor -- in motor representations?
>> Kate Possin: Yeah, I mean, that's a great question. Parkinson's is historically thought
of as really a pure motor disorder. But now we're really understanding that that's not the
Now, these patients are in the early stages of Parkinson's disease. They're not demented.
Many of them drive themselves the appointment; in fact, probably most of them were
able to. Many of them are still working if they're of that age. So these are nondemented
patients with Parkinson's disease. So these are very circumscribed impairments.
Now, some people would argue that in many patients the cognitive impairments actually
can even precede the motor sometimes. That definitely happens in some cases. And we
actually call that disease dementia with Lewy bodies, when the cognitive impairment
appears first.
>> These patients had some observable [inaudible].
>> Kate Possin: These patients definitely. They were diagnosed with Parkinson's motor
disease. But this is early. These are nondemented patients.
As you may have been picking up through my talk, one thing that Roland and Desney
and I have been very interested in is this distinction between allocentric and egocentric
navigation and these different brain regions that mediate them, because in Alzheimer's
disease they have this early problem with the medial temporal lobe, including the
hippocampus, and Parkinson's have early trouble with the dorsal caudate, which is
important for egocentric navigation.
So we're excited about testing out these navigation strategies in these patients because we
think we're going to see a real different pattern of deficits.
This is an example of our egocentric route learning test. On this test the subjects learn a
set route through an environment by trial and error. So the first time they go through
they're just guessing. But as they go through the environment several times, we'll give
them up to ten trials, over time they're going to get better. They're going to learn the
routine of going through the environment.
There's no useful boundary use like in that other task that I showed you, and really we're
finding in pilot testing that even our normal subjects are not building a cognitive map of
the environment. Instead, they're relying more on the relationship between local use, like
turn right at the red building, and also just a motor or routine kind of memory, kind of the
sequence of key presses or maybe driving simulator movements, if we hook it up to the
driving simulator.
So we think that this test is going to test that egocentric system that's subserved by the
caudate nucleus and it will be more impaired in Parkinson's disease than in Alzheimer's
>> Will you still consider it a motor -- or a spatial task if it's possible to have a strategy
where you're basically memorizing scenes and characters? It's a real tricky thing to
design, because the -- discovering the route is pretty spatial, but if I can really get to the
point where it's like LR, RLL, LR, it sort of ceases to become a spatial task then.
>> Kate Possin: I -- you know, I think you're making an excellent point. And I think that
there's a transition that happens when people are doing the test. I think at first they're
remembering turn right at the red building, but as they go through the test, it becomes
more of a motor memory, a routine.
>> Well, even a sort of -- verbal isn't the right word, but a truly semantic memory, like
I'm remembering LRR -- like I would never [inaudible].
>> Kate Possin: You could even use a verbalizable strategy to do this. Or you could just
sort of remember the movements. Absolutely.
>> I don't have any suggestions. It seems like a really hard problem to separate those
things apart.
>> Kate Possin: It is. And that's something that we've thought a lot about. And we're
thinking about ways to maybe tease that apart, and we have a lot of ideas for that.
On the other hand, I think that both of those kinds of learning are subserved by the
caudate nucleus. So I think it's still -- even if we don't tease it apart, I think it's still going
to be a really useful test for our purpose. But either we're not sure about if we're going to
do it in this version or down the road. We do want to tease apart those processes.
One thing I'm going to do is include an implicit learning motor memory kind of test on
the side so at least we can measure how well patient cans do that. But that's something -probably one of the biggest things we've been struggling with over the last few months.
So dementia does appear in almost all patients with Parkinson's disease before they die.
It's a different kind of dementia than Alzheimer's disease. In fact, visuospatial
impairment is even more prominent than in Alzheimer's disease.
When a patient is showing difficulty on a test of figure copy, it's a bad sign because it has
been shown that global cognitive decline is on the way. If the patient comes back a year
later, they're more likely to be demented. So visuospatial impairment is a really
important marker for incipient cognitive decline in Parkinson's disease.
So, yeah, these patients perform worse on average than Alzheimer's disease on tests of
figure copy. They have more trouble with visual attention than auditory attention.
When patients with Parkinson's disease have dementia, which is also called dementia
with Lewy bodies, they often have hallucinations, visual hallucinations in particular.
And they seem to share a similar neural basis with the visual perceptual problems. So
these patients often will see children or small people or animals frequently that aren't
>> Those Lewy body counts are measurable by imaging, or are those postmortem?
>> Kate Possin: Postmortem. They're not -- unfortunately, I wish they were measurable
by imaging. It would be -- it's hard to do imaging studies with Parkinson's disease,
actually, because atrophy isn't telling the whole -- isn't telling as much of the story as it
does with Alzheimer's disease. There's a lot of neurochemical abnormalities in
Parkinson's, and these Lewy bodies which are associated with cognitive impairment.
But I should say actually, I should have put this in my talk, perhaps, that we do real
comprehensive neuroimaging analysis with all of our patients.
And so we're really excited about looking at the relationship between performance on
these navigation tests and various neuroimaging indices, so we can see is -- do
hippocampal volumes correlate with performance on the allocentric task, and do caudate
volumes on the egocentric, and we can look at white matter tracts and also some
functional connectivity analyses to look at the different networks that may be involved.
This will help us really understand the neural bases of performance on our tests.
I'm going to turn now to the last family of diseases, frontotemporal lobar degeneration.
So these diseases preferentially impact the frontal lobes here and the most anterior front
part of the temporal lobe. So not the medial temporal lobe with the hippocampus that
we've been talking about in Alzheimer's, more the front tip of the temporal lobe.
Critical visuospatial processing areas like the dorsal and ventral streams in the back of the
brain are relatively spared. There are three syndromes in this disease, the most common
is the behavioral variant of frontotemporal dementia.
These patients typically present in their 50s or 60s, more often men than women, with
behavioral problems. Maybe they're making inappropriate, lewd comments or they have
been married to their wife for 30 years but started having an affair with their next-door
neighbor and couldn't care less how that affects their wife.
There's a loss of empathy for what other people think and feel. There's a loss of disgust.
They might not see a need to take a shower or they might not see what's wrong with
pulling a half-drunk empty can of Diet Coke out of the garbage and start drinking from it.
They might start eating a lot more food than they used to, and particularly sweet foods.
They don't really care if it has nutritional value.
So these are the kind of symptoms that we see first. And as you can imagine, they
typically get referred to psychiatry or just thought to be a bad person, rather than getting
into see us as quickly as we would like.
When there are cognitive problems, they are involving the executive, higher-level
planning aspects of cognition subserved by their frontal lobes.
There are also two language syndromes, progressive nonfluent aphasia and semantic
dementia. In progressive nonfluent aphasia, the patients have trouble initiating speech
and communicating with language, even though they understand language quite well.
They just can't get it out. They also can have trouble with writing it as well.
Semantic dementia, there's a loss of semantic knowledge. So you might say to a patient,
you know, please get me the can opener, and they might look at you with a perplexed
face like they've never heard the word can opener before. And even when you hand them
the can opener, they don't know what to do with it. They've forgotten what that is.
Other forms of memory, like where did you go for dinner last night, like that kind of
memory which we see so affected in Alzheimer's disease, is less affected in semantic
So talking about the first of those three syndromes, the behavioral variant of FTD, these
patients have predominantly frontal atrophy. It's worse on the right than on the left in this
disease, so there is an asymmetry here. And these patients showed top-down executive
control problems.
I was going to show you some clinical examples. This is a patient who has no dementia.
On that global scale of cognitive function called the MMSC, he scored a perfect score.
He's working as a lawyer, traveling around the world, giving talks, you know,
functionally doing quite well except for a lot of behavioral problems, which are very
upsetting to his wife.
And he's doing pretty well at copying this figure. The only -- I wouldn't -- if a normal
control did this, I wouldn't think anything. But, you know, there was some poor
planning. He drew this rectangle before he drew the X, and so he had to kind of scoop
around there. Nothing to, you know, make a big deal out of, but I think there was a little
bit of poor planning there.
Here's that same patient. Again, totally working, driving, doing all this stuff. He's told
on this test of design fluency, which is a top-down visuospatial test, he has to create as
many different designs as he can using only four lines. Those are the only rules. They all
have to have four lines and they all have to be different.
He's very concrete in his approach. He only does one type of design. You could imagine
there's a lot of different ways to do this. So kind of stuck in set in his thinking. And also
he makes a lot of repetition errors. He perseverates. And we're writing up a paper right
now that shows that these patients just very frequently make these kinds of errors on this
test, and it's associated with their frontal atrophy.
>> Is this the defining diagnostic character here, or is there also imagining representation
of the FTD also at this point?
>> Kate Possin: At this point, yeah. We can see something on imaging. But really at
this point what's convincing us the most is that this patient is showing the clinical
syndrome of FTD, which is most -- we put the most weight on these behavioral
symptoms. So saying inappropriate things, lack of empathy. Not putting on a fresh shirt,
just feeling what's wrong with wearing the same shirt five days in a row.
These behavioral symptoms are what's convincing us the most. However, we could see
subtle signs on the brain imaging and these really subtle signs on testing that I'm pointing
>> With tests like this, if you gave it to him a week later and said -- or do you see any
repeats or repeat a pattern [inaudible] yes or [inaudible] no?
>> Kate Possin: That's a good question. Can they notice -- I do remember giving him
this test and I kept prompting him to make every design different, and he said I am
making them all different. But that's not -- so I don't know. I'm not really sure if -- what
he would say. That's a great question. I'm going to try it out with one of the patients.
>> [inaudible] no treatment really for this? Is that accurate? Is there any ->> Kate Possin: There's some symptomatic treatments for FTD. We are -- we do have a
clinical trial right now that's targeting the tau protein that aggregates in this disease. But
there are no disease-modifying treatments available right now.
>> Do these diseases occur in combination? Or is that rare?
>> Kate Possin: Well, that's a good question. You know, frequently the Parkinson's
dementia and Alzheimer's occur together. In fact, almost all patients who have Lewy
body dementia or Parkinson's with dementia have some Alzheimer's pathology in the
brain. So those tend to overlap a lot. But FTD, occasionally, but not -- not more than
just by chance, I think.
This is a patient with a -- so more cognitively impaired than the previous patient. Mild
dementia. On that global score that was 0 to 30, this patient got a 23. This patient had
really poor organization. Rather than doing just a box and then the X, sort of a piecemeal
approach drawing the different segments, oversimplifying some of the elements of the
So this patient, like an Alzheimer's patient, is going to get a bad score on this test but for
a different reason.
This is a patient with FTD but much more severe dementia. This patient was actually
mute. Couldn't even speak anymore the disease was so bad. Visuospatial processing
from a bottom-up perspective might not be that bad, because, after all, the patient could
draw a box and this little X despite being severely, severely demented, but perseverates
on this overlearned response of writing her name.
By the way, I redrew this figure with a different name to protect the patient's privacy.
But every time you put a pen in this patient's hand, she can't help but start to write her
name. It's an overlearned automatic response coming from the back of the brain. And
the front of the brain can't inhibit it. So that's getting in the way of her doing visuospatial
skills in just about anything she does.
This is the test of -- a test of inhibitory spatial attention. We call it the flanker paradigm.
In this test the subject has to indicate the direction of this middle arrow. So here you'd
say it's pointing to the right. On some trials these flanking arrows point in the same
direction as the middle arrow, which makes it easier for you to respond. You're quicker.
On other trials they point in the opposite direction, which actually is going to slow you
down, because that's inhibiting competing information. So even healthy controls are
going to be slower when the flanking arrows point in the opposite direction.
And this affect is even more striking in FTD. So these are FTDs with no cognitive
impairment on traditional tests. So they're just having behavioral problems but
performing pretty well on our gold-standard tests. And they're just as fast as the controls
on the congruent condition. But when the flanking arrows point in the opposite direction,
they show increased slowing.
So these patients are having trouble inhibiting irrelevant information and focusing on
what is relevant using their frontal lobes.
And lastly I'm going to talk about these language variants of FTD. And then, by the way,
we're going to have plenty of time for questions or going home early.
But, anyway, these variants have excellent visuospatial skills. Progressive nonfluent
aphasia, there's atrophy in the front left part of the brain. So, remember, the right side of
the brain is really important for visuospatial processing, the left is more important for
language. And the left front is important for language output.
So these patients have trouble producing language and communicating, even though they
can understand language, because the back part of their brain that understands the
language is relatively intact.
Semantic dementia, those are the patients who have the loss of semantic information, like
what is a can opener, these patients have damaged the anterior temporal lobe. So that
lobe that's right here by the ears, the have front part, that part of the brain seems to be
critical for remembering semantic information.
So these patients, even when their language is so bad that they can't speak or they can't
understand what you're saying to them, you put a complex figure in front of them, they
can copy it just as well as you or I.
So the visuospatial processing from the back of the brain is just really good and even
those executive aspects that are affected in the behavioral variant are also pretty good.
Why am I talking about them, to talk about visuospatial cognition? Well, in many of
these patients we see an emergence of artwork. These patients become fascinated with
the visual world. In some patients the art can take on a compulsive quality. They don't
want to do anything else. They just want to live in that visual world, that visual
In semantic dementia, we do see sort of a loss of symbolism or abstraction in the art,
probably because of the loss of semantic information. But that's not true for the
nonfluent variant of FTD.
So I'll give you one case example. Although, we have so many that we see at our clinic.
Our clinic is -- one of our specialties is this family of disorder, so we've become very
interested in this.
We had this one patient whose name was Anne Adams who freely shares her name. In
fact, you could read all about her on our Web site. She was a professor of mathematics,
so a very left-brained person. Math is really a left-brained task.
And midlife, I think it was in her 50s, I believe, her son was in an accident and she left
work to take care of him. Well, he recovered very quickly and she decided not to go back
because she was interested in making art for the first time in her life.
And at first the art was quite realistic. But over time it became more abstract and began
to take a transmodal quality. So she liked, for example, to represent musical
compositions in visual form.
This is one of her paintings. Now, this is of her visual representation of Ravel's Bolero,
which you may or may not know. It's probably his most well-known piece, and it has
very sort of compulsive, organized, repetitive quality to it.
And what she's done is she's come up with all these different rules for how to represent
the different phrases in the piece. I forget them offhand, but it's like the height might
represent the pitch and the color might represent the duration of the note, for example.
So if you -- you can actually play this song and follow -- we had -- the person who wrote
up this case study did this for us, with a pointer followed along as we listened to Bolero
and saw the song.
>> The patient can actually verbalize those rules, has a conscious semantic understanding
of those rules, it's not just something that it's retrospectively discovered from the ->> Kate Possin: Yes. So she verbalized the rules. So she painted this before the
language symptoms began. She painted this just about a year or so before.
>> She said I'm now going to pitch to position or whatever ->> Kate Possin: She did. In fact, you can -- yeah. I can show you -- anyone the
manuscript, if you're interested. I just read it recently, and she had laid it all out very
She also liked to represent abstract concepts in visual form. For example, the number pi
she represented in visual form.
So this sort of transmodal, crossing concepts aspect became very fascinating to her.
As the disease -- the disease began and she started to lose her ability to express herself.
She had that nonfluent form of aphasia affecting the front part of her brain. And she just
became more immersed in the visual world, having more and more success as an artist.
So why -- uh-huh.
>> The emergence of that fascination, is that -- it's not really [inaudible] new ability. Is
there an understanding of why -- is that -- this is just an analogy, maybe, is that
anatomically related to sort of motor representations taking over motor regions and if you
tease that kind of thing where it's literally that adaptation to the lack of function in certain
areas that -- but it's happening in the frontal cortex so it manifests as a fascination? Is
there an understanding of why you -- where that fascination comes from?
>> Kate Possin: Why that would happen. So there's a few -- there's three major theories
I can think of about why this might happen. One is that these patients can't use their
language, but they can use their visuospatial skills. That's an intact area for them. That
part of the brain is still working. So they spend time there because they can use those
skills. And just by practice alone they get better and they get more enjoyment out of it
because it's something they can do whereas language is frustrating. Yes.
>> This seems a mirror image of the old tradition of the blind poet.
>> Kate Possin: The blind poet. Yes.
>> Homer, who allegedly could not see, so he had poetry.
>> Kate Possin: Exactly. Exactly. So maybe they just -- they do what they can do.
>> It sounds like it has a little bit more [inaudible] a little bit more of a compuls- -pathologically compulsive quality than just like a -- I've discovered a new thing that's fun
for me.
>> Kate Possin: Yeah. Yes. And I think most people in our group would agree with
you. And the reason that -- so our people that I work with, their theory is that parts of
your brain are always inhibiting other parts of your brain. The left hemisphere is
inhibiting the right, the right's inhibiting the left. The front's inhibiting the back, the
back's inhibiting the front.
If you get select cell death in the left front of your brain, you're releasing the functions of
the back right part of your brain.
And interestingly, if you look at her MRI scan, the right back of her brain is actually
bigger than the right back of the brain of control subjects. And if you look at perfusion,
so, you know, using sugars in the brain, that part of the brain is using more. There's
hyperperfusion compared to controls.
So that's another theory. And I think that's a theory that the person who wrote this paper
would probably ascribe to. But it's very controversial.
There are some other people who disagree and think, well, there's actually some mild
distortions that are interesting to us viewers, and that's just because of the brain damage.
So these interesting distortions or creativity in the work weren't really done for effect,
they're just a symptom of the brain damage.
>> [inaudible] there's some people who have hallucinations when they hear music. I
can't remember the name of it.
>> Kate Possin: Oh, synesthesia.
>> Yeah. Did she report similar ->> Kate Possin: She did not have synesthesia. But that's an excellent question because it
kind of seems like maybe ->> The colors.
>> Kate Possin: -- she did based on this, she was assigning colors to mean something
related to sound. But she was asked that and she didn't report that symptom.
There's one interesting twist to this story. So she became just obsessed with Maurice
Ravel who wrote this musical piece but did not know that Maurice Ravel actually had the
same exact disease.
So around the time that he created this song, he was in the earliest stages of this same
kind of language dementia that this woman had, and similarly became sort of obsessed
with order and organization in a compulsive way, which I think is reflected in this song
that she became fascinated with.
So, in summary, we talked about the three most common causes of neurodegenerative
disease today and focused on their visuospatial cognition.
In Alzheimer's disease we see dysfunction of both where and what processing, that's the
dorsal and ventral stream processing, and we hypothesized that early on in the disease
they might have a problem with allocentric navigation because of the medial temporal
lobe atrophy.
In Parkinson's disease we see more dorsal or location-based processing than we do
object-based processing specifically affecting aspects of attention and working memory.
And we hypothesized that they may have more egocentric impairment early on because
of the dysfunction involving the caudate nucleus and its circuits with the frontal and
parietal lobes.
In Parkinson's disease with dementia, the visuospatial problems are more prominent and
widespread than in Parkinson's disease without dementia.
And frontotemporal lobar degeneration, there's the three variants. In the behavioral
variant, they have trouble with executive or top-down aspects of visual cognition. And
the language variants have excellent visuospatial cognition and the -- and severe language
If you want to learn more about what we do at our group, I encourage you to take a look
at our Web site. And also we have a channel on YouTube where we have a lot of videos
of some of our faculty talking about these diseases and we have some -- I think we also
have some videos of our patients showing some of the symptoms.
We don't have too many visuospatial videos yet. I'm actually working on that. I want to
show some videos of what these different visuospatial impairments look like. We have a
lot of videos of those behavioral impairments that you see a lot in FTD on this site.
So, anyway, it's been a real honor to get to share what I've been working at with all of
you. I don't know exactly where I'd be right now with my research if I hadn't been so
lucky as to form this collaboration with your group. And I think that this collaboration is
representing a possible new path to where neuropsychology can go five and ten years
down the road. So thank you for that opportunity.
>> Kate Possin: Yeah.
>> You mentioned briefly that there's -- there are affects on practice and mental exercise
on [inaudible] development and [inaudible] about how education and mental engagement
can delay the onset of dementia.
Do you think that the virtual environments you're talking about so far have been purely
diagnostic? Do you think those effects are actually robust enough that, in principle, you
could as a treatment have somebody work in a virtual environment for an hour or two
hours a day or whatever [inaudible] slow onset of Alzheimer's or Parkinson's?
>> Kate Possin: That's a very tough question. And definitely controversial. There are a
number of companies out there right now that are making money by selling cognitive
exercise products to patients who have Alzheimer's disease. And I think in general the
research with those kinds of puzzles and things don't show that they necessarily help
more than just engaging the brain.
So we encourage our patients to use their brain but to use it in a way that's fun for them.
Maybe, but it's hard to know if at that point it's really going to help to selectively use your
hippocampus over an over again.
But the research with the taxi drivers suggests -- it's a question -- I don't know if it's been
directly answered. I wonder if those taxi drivers are going to be less likely to get
Alzheimer's disease.
>> Or less [inaudible] really reliable genetic markers, so that really pre-onset you can
reliably predict the eventual onset of Alzheimer's and Parkinson's, and then it might be -then it's not maybe too late to actually selectively exercise your hippocampus if you can
predict that [inaudible].
>> Kate Possin: If I were in that situation, I would do it. Yeah. We don't have the data
to support it, but I think there's reason ->> [inaudible] a day every day ->> Kate Possin: Yeah. Yeah. Right. I'd throw out MapQuest and force myself to learn
where things are and, yeah, generate a cognitive map.
>> Or just get a second job as a taxi driver.
>> Kate Possin: Or -- yeah, exactly. And, you know, that's not that far off either.
There's new imaging techniques where we can actually image the amyloid deposition that
we see in Alzheimer's disease, so we can see the pathological proteins now in vivo. We
also have cerebral spinal fluid tests where we can measure these proteins.
So for Alzheimer's disease, we're pretty good, I think. We don't use these tests clinically,
but we use them in our research. So we're pretty good at determining who is going to get
Alzheimer's and who isn't with these tests. We think. We're still researching them.
>> I'll keep asking questions if no one else has questions. Are there -- so you've also
talked about late onset -- only late onset diseases. Are there congenital diseases that
happen in children or adolescence that have similar manifestations that this type of
diagnostic [inaudible] also? I've never heard of any, I just wondered ->> Kate Possin: Yeah, that's a great question. I'll have to be honest. It's not my area of
specialty. But it's very likely. I'm thinking like fetal alcohol syndrome, I know they have
a lot of subcortical problems. But, yeah, certainly it could be useful for other diseases
where these brain areas are important. Often seizure disorders involve the medial
temporal lobe. Yeah.
Although, some of these diseases can start earlier than you think. I had a patient last
week who was in his late 30s, a professional football player. Because of all of the head
injuries, the concussions he'd had, he's coming down with an early onset form of
Alzheimer's disease. In his late 30s.
>> Is that pathologically similar, Alzheimer's, in cases where it was actually induced by
injury, if you'd still diagnose it as the same kind of Alzheimer's that ->> Kate Possin: It's not exactly the same. It is a little bit different.
>> That would be stunning if it -- I sort of just think of the Alzheimer's as having a -either a genetic or a chemical origin would be sort of -- seems like astonishing
research-wise if it could actually manifest similarly based on [inaudible] injury.
>> Kate Possin: Yes. It shares some features, like it has this pathological tau protein that
we see in Alzheimer's, but it doesn't have as much of the amyloid. It has a slower
progression. Often has Parkinsonian features. Muhammad Ali may have this type of
Well, thank you all. And I'm going to be here all day tomorrow too. And I'd be most
pleased to have discussions with any of you or to have you come on by and try out one of
our tests.