Download Learning, Memory, and Amnesia

Module 12.1:
Learning, Memory, and Amnesia
Learning, Memory, and Amnesia
• An early influential idea regarding localized
representations of memory in the brain suggested
physical changes occur when we learn something new.
• One popular idea was that connections grow between
areas of the brain.
Learning, Memory, and Amnesia
• Ivan Pavlov researched
classical conditioning in which
pairing of two stimuli changes
the response to one of them.
– Presentation of a
conditioned stimulus (CS) is
paired with an unconditioned
stimulus (UCS).
– Automatically results in an
unconditioned response
(UCR).
• After several pairings, response
can be elicited by the CS
without the UCS, which is
known as a conditioned
response (CR).
Ivan Pavlov
(1849-1936)
Learning, Memory, and Amnesia
• In operant conditioning,
responses are followed by
reinforcement or punishment
that either strengthen or
weaken a behavior.
– Reinforcers are events
that increase the
probability that the
response will occur again.
– Punishment are events
that decrease the
probability that the
response will occur again.
Learning, Memory, and Amnesia
• Pavlov believed that
conditioning strengthened
connections between the
CS center and UCS center
in the brain.
• Karl Lashley set out to
prove this by searching for
such engrams, or physical
representations of what
had been learned.
– Believed that a knife cut
should abolish the
newly learned response.
Karl Lashley
(1890-1958)
Learning, Memory, and Amnesia
• Lashley’s studies
attempted to see if
disrupting certain
connections between
cortical brain areas would
disrupt abilities to learn
associations.
• Found that learning and
memory did not depend on
connections across the
cortex
• Also found that learning did
not depend on a single
area of the cortex.
Learning, Memory, and Amnesia
• Lashley proposed two key
principles about the nervous
system:
• Equipotentiality – all parts
of the cortex contribute
equally to complex
functioning behaviors (e.g.
learning)
• Mass action – the cortex
works as a whole, not as
solitary isolated units.
Learning, Memory, and Amnesia
• Research by Richard
F. Thompson and
colleagues focused
on the cerebellum’s
role in classical
conditioning.
• During an eye-blink
conditioning task in
rabbits, changes
were recorded in
cells of the lateral
interpositus nucleus
(LIP).
Richard F. Thompson
(1930-2014)
Learning, Memory, and Amnesia
• Suppression of activity
(through application of
drugs or cooling the LIP)
led to a condition in which
the subject displayed no
previous learning.
• As suppression wore off,
the animal began to learn
at the same speed as
animals that had no
previous training.
• Red nucleus of the
midbrain found to
temporarily suppress a
response, but not learning
Learning, Memory, and Amnesia
Donald Hebb (1904-1985) differentiated between
two types of memory(1949):
Short-term memory (STM)– memory of
events that have just occurred
• Limited capacity
• Fades quickly
• Not affected by cues
Long-term memory (LTM)– memory of
events from previous times
• Unlimited capacity
• Memories persist over time
• Can be stimulated with a cue
Learning, Memory, and Amnesia
• Later research weakened the
distinction between STM and
LTM.
– Some memories do not
qualify as distinctly shortterm or long-term.
• Working Memory
– Proposed by Baddeley &
Hitch (1994) as an alternative
to short-term memory
– Emphasis on temporary
storage of information to
actively attend to it and work
on it for a period of time
Alan Baddeley & Graham Hitch
Learning, Memory, and Amnesia
Three major components of working memory include:
• Phonological loop – Stores auditory input
• Visuospatial sketchpad – Stores visual input
• Central Executive – Directs attention and determines which
items to store
Learning, Memory, and Amnesia
• The delayed response task is a test of working memory which
requires responding to a stimulus that one heard or saw a
short while earlier.
• Increased activity in the prefrontal cortex during the
delay indicates storing of the memory.
• The stronger the activation, the better the performance.
Learning, Memory, and Amnesia
• Older people often have impairments in working memory.
• Changes in the prefrontal cortex assumed to be the cause.
• Declining activity of the prefrontal cortex in the elderly is
associated with decreasing memory.
• Increased activity is indicative of compensation for other
regions in the brain.
Learning, Memory, and Amnesia
• Amnesia is the loss of memory.
• Studies on amnesia help to clarify different kinds of
memories and their mechanisms.
• Different areas of the hippocampus are active during
memory formation and retrieval.
– Damage results in amnesia.
Learning, Memory, and Amnesia
• Patient HM is a famous case study in psychology who had
his hippocampus removed to prevent epileptic seizures.
• Afterwards HM had great difficulty forming new long-term
memories.
• STM or working memory remained intact.
• Suggested that the hippocampus is vital for the formation of
new long-term memories.
Learning, Memory, and Amnesia
• Patient HM showed massive anterograde amnesia after
the surgery.
• Two major types of amnesia include:
• Anterograde amnesia – the loss of the ability to form
new memory after the brain damage occurred.
• Retrograde amnesia – the loss of memory events prior
to the occurrence of the brain damage.
Learning, Memory, and Amnesia
• Patient HM had difficulty with declarative and episodic memory.
– Episodic memory: ability to recall single events
– Declarative memory: ability to put a memory into words
• HM’s procedural memory remained intact.
– Procedural memory: ability to develop motor skills
(remembering or learning how to do things)
Learning, Memory, and Amnesia
• HM also displayed greater “implicit” than “explicit” memory.
– Explicit memory – deliberate recall of information that
one recognizes as a memory
– Implicit memory – the influence of recent experience on
behavior without realizing one is using memory
Learning, Memory, and Amnesia
• Hippocampus activity is more
associated with memory
performance than is the size.
• The hippocampus is:
1. critical for declarative
(especially episodic)
memory functioning
2. especially important for
spatial memory
3. especially important for
configural learning and
binding.
Learning, Memory, and Amnesia
• Research in the role of the hippocampus in episodic memory
shows damage impairs abilities on two types of tasks:
• Delayed matching-to-sample tasks – a subject sees an
object and must later choose the object that matches.
• Delayed non-matching-to-sample tasks– subject sees an
object and must later choose the object that is different
than the sample.
Learning, Memory, and Amnesia
Damage to the hippocampus
impairs abilities on spatial
tasks such as:
• Radial mazes – a subject
must navigate a maze that
has eight or more arms
with a reinforcer at the
end.
• Morris search task – a rat
must swim through murky
water to find a rest
platform just underneath
the surface.
Learning, Memory, and Amnesia
• Hippocampus damage impairs
configural learning and binding:
– Configural learning –
learning in which the
meaning of a stimulus
depends on what other
stimuli are paired with it.
– Animals with damage can
learn configural tasks but
learning is slow.
• Indicates hippocampus is
not necessary for
configural learning, but is
involved.
Learning, Memory, and Amnesia
• Evidence suggests that the
hippocampus is important in
the process of “consolidation”.
• Consolidation is the process of
strengthening short-term
memories into long-term
memories.
• Damage to the hippocampus
impairs recent learning more
than older learning.
– The more consolidated a
memory becomes, the less
it depends on the
hippocampus.
Learning, Memory, and Amnesia
• Consolidation is influenced
by the passage of time and
emotions.
– Small to moderate
amounts of cortisol
activate the amygdala
and hippocampus
where they enhance
storage and
consolidation of recent
experiences.
– Prolonged stress
impairs memory.
Learning, Memory, and Amnesia
•
•
Different kinds of
brain damage
result in different
types of amnesia.
Two common
types of brain
damage include:
1. Korsakoff’s
syndrome
2. Alzheimer’s
disease
Learning, Memory, and Amnesia
• Korsakoff’s syndrome –
prolonged thiamine (vitamin
B1) deficiency impedes the
ability of the brain to
metabolize glucose.
• Leads to loss or shrinkage of
neurons in the brain
• Often due to chronic
alcoholism
• Symptoms include apathy,
confusion, and forgetting and
confabulation (taking guesses
to fill in gaps in memory).
Learning, Memory, and Amnesia
• Alzheimer’s disease is
associated with a
gradually progressive
loss of memory often
occurring in old age.
• Affects 50% of people
over 85.
• Early onset seems to be
influenced by genes, but
99% of cases are late
onset.
• About half of all patients
with late onset have no
known relative with the
disease.
Learning, Memory, and Amnesia
Alzheimer’s disease is associated with an accumulation and
clumping of the following brain proteins:
• Amyloid beta
protein 42 which
produces
widespread atrophy
of the cerebral
cortex,
hippocampus and
other areas.
• An abnormal form
of the tau protein,
part of the
intracellular support
system of neurons.
Learning, Memory, and Amnesia
• Accumulation of
amyloid beta and tau
proteins results in:
– Plaques –
structures formed
from degenerating
neurons
– Tangles – structures
formed from
degenerating
structures within a
neuronal body
Learning, Memory, and Amnesia
• A major area of damage is the basal
forebrain and treatment includes
enhancing acetylcholine activity.
Donepezil (Aricept)—
cholinesterase inhibitor
Learning, Memory, and Amnesia
• Lessons from studying
amnesiac patients
include:
– One can be deficient
in several different
aspects of memory.
– There are
independent kinds of
memory.
– Various kinds of
memory depend on
different brain areas.
Head Shot: In this diffusion spectrum
image, fiber bundles are color coded
according to their directions of impulse
transmission. The Human
Connectome Project uses diffusion
spectrum and other cutting-edge
neuroimaging techniques to map fiber
pathways in the normal human brain.