Introduction to
Physiological Psychology
Learning and Memory II
ksweeney@cogsci.ucsd.edu
cogsci.ucsd.edu/~ksweeney/psy260.html
Memory
Working Memory
Long-term Memory
Declarative
Memory
Episodic
Memory
Procedural
Memory
Semantic
Memory
1
What can possibly go wrong?
n
Anterograde Amnesia:
– Amnesia for events occurring after the
precipitating event.
n
Retrograde Amnesia:
– Amnesia for events occurring before the
precipitating event.
Hippocampus 3D
2
H.M.
Effects of Bilateral Medial Temporal Lobectomy
Minor seizure beginning at age 10, major
seizures beginning age 16
n Severe, persistent seizure condition- not
controlled with anticonvulsants
n By mid-20ʼs, condition was so severe he
was unable to work
n Surgery at age 27:
Bilateral medial temporal lobe resection.
n
Tissues typically
excised in
medial temporal
lobectomy
3
n
In HM, the
amygdala,
entorhinal and
perirhinal cortices,
and about twothirds of the
hippocampus were
removed
4
H.M.
Effects of Bilateral Medial Temporal Lobectomy
Seizures were dramatically reduced – but
so was his long-term memory!
n Evaluation two years post-surgery (April, 1955)
n
– Gave date as March 1953, and age as 27
– Talked to physician before entering exam room, but at exam
had no recollection of him
– Memories of his past were clear
– No deficits in perception, abstract thought, reasoning
– As he progressed through tests, retained no memory of earlier
tests, and didnʼt recognize them when presented a second
time.
Whatʼs wrong with H.M., and what does it tell us
about functions of Hippocampus and MTL?
n
What CAN he do?
– Intellect is normal
– Can remember the past (pre-surgery)
§ He has relatively little retrograde amnesia
§ His long-term memory is intact
– Can carry on excellent, short conversation
§ His working memory is intact
– Can learn new skills at a normal rate- and
retains those skills over long periods of time
§ His procedural memory is intact
5
n
Procedural memory is intact!
– Rotary Pursuit task
– Mirror Drawing task
Other spared learning
“Broken drawing” recognition
n Preference task
n
– melodies
– Valenced faces
Repetition priming
n Serial reaction time task
n
6
Whatʼs wrong with H.M., and what does it tell us
about functions of Hippocampus and MTL?
n
What CANʼT he do?
– Doesnʼt retain new semantic or episodic
information
– Canʼt form new declarative memories.
The Medial Temporal Lobe:
Crucial in the Declarative Memory System
n
n
n
Damage to these areas
usually results in
anterograde amnesia:
patients are unable to
form new declarative
memories.
Can also result in
retrograde amnesia:
typically ʻgradedʼ.
Non-declarative
memory is not affected.
7
What does H.M. tell us about role of
Hippocampus and MTL?
Hippocampus is essential for the formation,
but not the storage or retrieval, of long-term
declarative memory
n Memory depends on Hippocampus for a short
duration
n Hippocampus does not mediate short-term
memory
n
What does H.M. tell us about
role of Hippocampus and MTL?
n
STM and LTM are distinctly separate
– H.M. is unable to move memories from STM to
LTM, a problem with memory consolidation
n
Memory may exist but not be recalled – as
when H.M. exhibits a skill he does not know
he has learned
8
Explicit vs. Implicit Memories
n
Explicit memories – conscious memories
n
Implicit memories – unconscious memories,
as when H.M. shows the benefits of prior
experience
– Repetition priming tests- word fragments
– Incomplete pictures test- picture fragments
§ Also, new songs, response to ʻstrangerʼ
Medial Temporal Lobe Amnesia
Often (but not always) unable to form new
explicit long-term memories
n Semantic memory (general information)
may function normally while episodic
memory (events that one has experienced)
does not
n
– able to learn facts, but do not remember
doing so (the episode when it occurred)
n
Medial temporal lobe amnesiacs may have
trouble imagining future events
9
Spared Leaning Abilities
Perceptual Learning: Intact
n Stimulus-Response Learning: Intact
n Motor Learning: Intact
n
n
But Relational Learning…
Hippocampus 3D
10
11
Information pathway in
hippocampal formation
n
n
n
n
Entorhinal cortex >
Dentate gyrus >
CA3 >
CA1 & forebrain
Long Term Potentiation
n
n
n
n
Deliver single pulse to
perforant path
Measure population EPSP in
dentate gyrus
Stimulate perforant path
with series of rapid pulses
After rapid stimulation
response in dentate gyrus to
a single pulse is increasedLTP has occurred!!
12
Associative LTP
n
Exactly as Hebb had suspected: when
both a weak and a strong synapse are
stimulated at ~the same time, the weak
synapse becomes strengthened.
n
“Neurons that fire together, wire together”
13
Remember Temporal Summation?
The reason many
pulses are
necessary is
because for LTP to
occur, the
postsynaptic cell
must already be
depolarized.
n Why?
n
Temporal summation
NMDA and AMPA
n
n
n
Among the glutamate receptors: NMDA and AMPA
Glutamate binds to NMDA receptors, which controls a
calcium (Ca2+) channel.
So, Ca2+ rushes in, right? NO!
14
NMDA and AMPA
n
n
n
At rest, that same calcium channel is ʻguardedʼ by a
magnesium ion (Mg2+), so calcium canʼt get in through
NMDA receptors.
That Mg2+ ion wonʼt budge unless cell is depolarized.
But cell canʼt depolarize unless Ca2+ can get in, right?
NO!
NMDA and AMPA
n
n
If a weak synapse is active by itself, nothing happens…
BUT- if the cell has just fired due to a strong synapse
elsewhere else on the cell, a dendritic spike will
depolarize the membrane…
15
NMDA and AMPA
n
n
Depolarization kicks the Mg2+ ion out, and NOW Ca2+
ions can enter the cell.
… and an association between those two synapses is
formed.
We still donʼt have LTP!
n
n
n
Ca2+ ions entering the cell bind with the enzyme CaMKII
CaM-KII causes more AMPA receptors to to move to
post-synaptic membrane.
More AMPA receptors means itʼs easier to depolarize
the cell in the future.
16
We still donʼt have LTP!
n
n
n
Ca2+ ions entering the cell bind with the enzyme CaMKII
CaM-KII causes more AMPA receptors to to move to
post-synaptic membrane.
More AMPA receptors means itʼs easier to depolarize
the cell in the future.
For Ca2+ to enter the cell, NMDA
receptors have to be activated by
glutamate AND subjected to
depolarization simultaneously.
n The fact that both these things must
occur together means that NMDA
receptors are “coincidence detectors”.
n Thus, they are crucial for LTP.
n
17
Perceptual Learning
n
Learning enables us to adapt to our environment and
to respond to changes in it:
– In particular, learning provides us with the ability to
perform an appropriate behavior in an appropriate
situation.
n
The first part of learning involves learning to
perceive particular stimuli:
– Perceptual learning involves learning to recognize things,
not what to do when they are present.
n
Perceptual learning can involve learning to recognize
entirely new stimuli, or it can involve learning to
recognize changes or variations in familiar stimuli.
18
Perceptual Learning
n
Visual information:
– After the first level of analysis the information is
sent to the extrastriate cortex, which surrounds
the primary visual cortex (striate cortex, V1).
n
After analyzing particular attributes of the
visual scene, such as form, color, and
movement, subregions of the extrastriate
cortex send the results of their analysis to
the next level of the visual association
cortex, which is divided into two “streams.”
Perceptual Learning
n
The ventral stream
– involved with object
recognition, continues
ventrally into the inferior
temporal cortex.
n
The dorsal stream
– involved with perception of
the location of objects,
continues dorsally into the
posterior parietal cortex.
n
The ventral stream is
involved with the what of
visual perception; the dorsal
stream is involved with the
where.
19
PET study of where/what dichotomy
Perceptual Learning
n
Specific kinds of visual
information can activate
very specific regions of
visual association cortex.
n
The investigators presented
subjects with photographs
that implied motion—for
example, an athlete getting
ready to throw a ball.
n
They found that photographs
like these, but not
photographs of people
remaining still, activated
area MT/MST.
20
Stimulus-Response Learning
(Classical Conditioning)
Extinction
Several trials of the tone-alone (with no shock given).
Intact rats show normal blood pressure and movement to the tone, following this
(extinction) training.
21
The Amygdala
n
n
n
The amygdala (almond) sits at
the tip of the hippocampus
It receives information from
virtually the entire brainafter different amounts of
processing
It projects to many areas, but
one of the strongest
projections is to the
entorhinal cortex!
The Amygdala
n
As a rat learns the pairing, (more)
neurons become more responsive.
But after several tones
without the pairing,
firing rates return to
baseline.
If rendered inactive,
conditioning does not
occur!
Firing in the lateral amygdala
22
Basic “Fear Circuitry”
Creation and Extinction of Fear Memories
n
n
The lateral nucleus of the amygdala receives
information from somatosensory system and
auditory system.
It projects (directly and indirectly) to central
nucleus, which mediates expression of fear
response
23
Creation and Extinction of Fear Memories
n
n
With a lesion to the lateral nucleus, a rat will
not learn the conditioned emotional response.
With a lesion to the central nucleus, the
conditioned response is reduced.
Stimulus-Response Learning:
Instrumental Conditioning
n
Instrumental conditioning is the means by
which we profit from experience
– If the response is already known, we need
strengthening of connections b/t neural
circuits that detect relevant stimuli, and
those that control the relative response
– If a new response is needed, then motor
learning will take place
24
Instrumental Conditioning
n
Circuits responsible for instrumental
conditioning begin in sensory association
cortices and end in motor association
cortex.
Instrumental Conditioning
n
Two major pathways from sensory to
motor association areas:
– Direct transcortical connections- involved in
STM, acquisition of episodic memories and of
complex behaviors that involve deliberation
or instruction (slow and laborious)
– Connections via the basal ganglia and
thalamus- which are involved as behaviors
become automatic and routine (fast and easy)
25
Basal Ganglia
n
n
Neostriatum (caudate
and putamen) receives
sensory info from all
areas of cortex
Projects to globus
pallidus, which projects
to premotor and
supplementary motor
circuits (involved in
planning and execution
of movements), and to
primary motor cortex
Basal Ganglia
n
n
Damage to neostriatum
makes it difficult to learn
to make a visually guided
response…
but does NOT disrupt
visual perceptual
learning.
26
Instrumental Conditioning
n
n
n
As we deliberately perform a complex behavior,
the basal ganglia receive information both
about the stimuli that are present and the
responses we are making.
At first the basal ganglia are passive
“observers” of the situation, but as the
behaviors are repeated again and again, the
basal ganglia begin to learn what to do.
Eventually, they take over most of the details
of the process, leaving the transcortical circuits
free to do something else- We need no longer
“think” about what we are doing.
Relational Learning
27
Relational Learning
n
Spatial Memory
n
Spatial information need not be declared
(we can demonstrate our topographical
memories by successfully getting from place
to place)…
BUT: people with anterograde amnesia are
often unable to consolidate information
about the location of rooms, corridors,
buildings, roads, and other important items
in their environment.
n
Relational Learning
n
Spatial Memory
n
Bilateral medial temporal lobe lesions produce
the most profound impairment in spatial
memory, but significant deficits can be produced
by damage that is limited to the right
hemisphere.
n
Functional imaging studies have shown that the
right hippocampal formation becomes active
when a person is remembering or performing a
navigational task.
28
Relational Learning
n
Relational Learning in Laboratory Animals
n
The discovery that hippocampal lesions produced
anterograde amnesia in humans stimulated
interest in the exact role that this structure plays
in the learning process.
n
Researchers have developed tasks that require
relational learning, and on such tasks laboratory
animals with hippocampal lesions show memory
deficits, just as humans do.
Relational Learning
n
Relational Learning in Laboratory Animals
n
The Morris water maze requires relational
learning; to navigate around the maze, the
animals get their bearings from the relative
locations of stimuli located outside the
maze—furniture, windows, doors, and so on,
but the maze can be used for nonrelational,
stimulus–response learning too.
29
Relational Learning
n
Relational Learning in Laboratory Animals
n
If rats with hippocampal lesions are always
released from the same place, they learn
this nonrelational, stimulus–response task
about as well as normal rats do.
n
However, if they are released from a new
position on each trial, they swim in what
appears to be an aimless fashion until they
finally encounter the platform.
30
Relational Learning
n
Relational Learning in Laboratory Animals
n
Place cells have ʻreceptive fieldsʼ in the
environment.
n
Place cells are active when the animal is in a
particular location in the environment; most
typically found in the hippocampal formationbut also in entorhinal cortex.
n
Evidence indicates that firing of hippocampal
place cells appears to reflect the location where
an animal “thinks” it is.
31
Hippocampus and spatial memory
Hippocampus seems to play role in spatial
memory in many species – not just rats!
n Food-caching birds
– caching and retrieving is needed for
hippocampal growth
n
Primate studies are inconsistent
– But perhaps due to poor design!
n
Taxi drivers!
The Hippocampus and Memory
for Spatial Location
n
So… Rhinal cortex plays an important role
in object recognition
n
Hippocampus plays a key role in memory
for spatial location
– Hippocampectomy produces deficits on Morris
maze and radial arm maze
– Place cells also found in entorhinal cortex
32