Frontiers of Science: Mind & Brain
Professor Daphna Shohamy
Department of Psychology
Zuckerman Mind, Brain, Behavior Institute
HOW MEMORY WORKS
The truth about memory
•
Memory is selective.
•
Robust but also vulnerable; accurate but often biased
•
A record of the past, but essential for planning the future
•
To create memories, there MUST be long-term
changes in your brain.
HOW?
WHERE?
Frontiers of Memory Research
Localization Hippocampus Plasticity
Space & Time
Is memory distributed or localized?
Tried to localize the engram - the
single location of a memory.
He failed to find it.
And concluded that
memories are distributed
throughout the brain.
Karl Lashley
1890-1958
Early evidence for localized memory
Brenda Milner
Sue Corkin
1918 -
1937 - 2016
A serendipitous discovery that changed
everything we know about memory and the brain
Patient H.M.
Surgery to treat intractable
epilepsy, at age 27.
The seizures were
localized to the medial
temporal lobe, centered
on the hippocampus.
Henry Molaison
1926 - 2008
Patient H.M.
Surgical removal of the MTL
Outcome of surgery
1. Treated seizures
2. Healthy recovery in
general
3. But…no new memories
Patient H.M.
No memories of new
people, places, moments
Anterograde amnesia
EPISODIC (or declarative) memory
Other kinds of learning
were fine
Selective memory
impairment
Patient H.M.
Two fundamental insights
1. Different parts of the brain support different kinds of
memory
Different kinds of Memory
A Taxonomy of Memory
*remember Lashley?
Measuring different forms of learning
Learning
from
feedback
CORRECT
70%
Memory
for
feedback
30%
Different kinds of Memory
Learning
from feedback
65
50
80
% correct
Damage to
the
hippocampus
% correct
80
65
50
Control Amnesics
80
% correct
% correct
80
Damage to
the basal
ganglia
65
50
Control Amnesics
Memory
for feedback
65
50
Control Parkinson’s
Control Parkinson’s
Different kinds of Memory
Learning
from feedback
65
50
80
% correct
Damage to
the
hippocampus
% correct
80
50
% correct
% correct
80
65
50
65
Control Amnesics
DOUBLE DISSOCIATION
Control Amnesics
80
Damage to
the basal
ganglia
Memory
for feedback
Control Parkinson’s
65
50
Control Parkinson’s
Patient H.M.
Two fundamental insights
1. Different parts of the brain support different
kinds of memory
2. A specific and critical role for the hippocampus
and medial temporal lobe in episodic memory
Questions?
Frontiers of Memory Research
Localization Hippocampus Plasticity
Space & Time
The hippocampus
*Implicated in Alzheimer’s, anxiety and stress
A slice of cortex visualized with “brainbow”
A slice of the hippocampus visualized with “brainbow”
The hippocampus
Neural circuits for memory
Creating memories in the healthy human brain
•
Henry was a single historical case study. What can
modern neuroscience teach us about the hippocampus
and memory?
What happens in the brain
when new memories are
formed?
Creating memories in the healthy human brain
Creating memories in the healthy human brain
In healthy people, the
hippocampus is more
active for experiences
that are later
remembered.
Converging evidence
for the role of the
hippocampus in memory.
The Hippocampus
How do neurons in the hippocampus create
memories?
Long-term changes in neurons
•
How does the hippocampus build memories? What does
a memory look like in a neuron?
Aplysia
Eric Kandel
Nobel prize 2000
Simple forms of memory.
Simple neural circuit.
Long-term changes in neurons
Activating a synapse
can make it stronger minutes, hours and
even days later.
Long term
potentiation (LTP)
Changes to dendrites
LTP
Neural plasticity
Plasticity is a key concept in learning, memory and
in brain function, in general
What we have learned so far…
•
The hippocampus (and nearby structures) are necessary
for building long-term episodic memories, but not for
other kinds of memories (e.g. habits, working memory).
•
The process of creating memories involves long-term
changes to synapses - strengthening of the connections
between neurons.
But, it turns out to be a little more complicated (& interesting)
1. The hippocampus and navigation
2. The hippocampus and future-thinking
Frontiers of Memory Research
Localization Hippocampus Plasticity
Space & Time
The hippocampus and navigation
Place Cells
Neurons in the hippocampus represent a spatial map
The hippocampus and navigation
O’Keefe, Moser, Moser
Nobel prize, 2014
Place Cells
Neurons in the hippocampus represent a spatial map
The hippocampus and navigation
Let’s listen* to some place cells in action
*Why listen? Remember that neurons
communicate with electrical activity. We can
record and amplify that activity to “listen” to
neurons firing.
The hippocampus and navigation
https://www.youtube.com/watch?v=bL0WLyMLwqw
The hippocampus and navigation
In humans too?
Place Cells in humans*
Virtual Reality Navigation
* Q: How can we record electrical activity from specific neurons in
the human brain? (would you volunteer your brain?)
A: Only from patients who are already undergoing brain surgery.
“What does this
have to do with
memory?”
The hippocampus and future-thinking
Converging
“Imagine youevidence
are lying onfor
a white
the role
tropical
of the
beach in a beautiful
tropical
hippocampus
in imagining
thebay”
future.
Prefrontal cortex
Hippocampus
Patients with amnesia have
trouble imagining future events
People use the hippocampus to
remember and to imagine
But, not just the hippocampus!
(also areas in the cortex)
Is memory distributed or localized?
Karl Lashley
Brenda Milner
Sue Corkin
1890-1958
1918 -
1937 - 2016
Distributed AND localized.
The right question, the wrong tools.
Questions?
Connecting the dots
Memory
Navigation
Imagination
Hippocampus
Binding elements of experiences in time and space
Experiment demo
Memory is biased.
It is shaped by motivation,
interests and goals.
Sometimes even AFTER
an experience.
A record of the past that
is used to guide behavior
in the future.
Connecting the dots
Memory
Navigation
Imagination
Hippocampus
Binding elements of experiences in time and space
A tight link between what we remember from
the past and what we decide to do in the future
Next week
How we make decisions
(* including research on patients with
Anorexia Nervosa)
thank you!