Transcript Learning, Memory, Amnesia, and Brain

Chapter 13:
Biology of Learning and
Memory
Learning, Memory, Amnesia, and Brain
Functioning
• An early influential idea was that physical
changes occur when something new is
learned or a memory is formed.
• Explanations was that connections grew
between areas of the brain.
– Led to the search for localized
representations of memory
Learning, Memory, Amnesia, and Brain
Functioning
• Ivan Pavlov pioneered classical conditioning
in which pairing of two stimuli changes the
response to one of them.
– A conditioned stimulus (CS) is paired with
an unconditioned stimulus (UCS) which
automatically results in an unconditioned
response (UCR).
• After several pairings, response can be
elicited by the CS without the UCS,
– New response is now called a conditioned
response (CR).
Learning, Memory, Amnesia, and Brain
Functioning
• In operant conditioning, responses are
followed by reinforcement or punishment that
either strengthen or weaken the 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, Amnesia, and Brain
Functioning
• 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.
Learning, Memory, Amnesia, and Brain
Functioning
• 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 entirely on connections across the
cortex
• Also found that learning did not depend on a
single area of the cortex.
Learning, Memory, Amnesia, and Brain
Functioning
• 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, Amnesia, and Brain
Functioning
• Richard F. Thompson et. al. suggested that
the engram for classical conditioning is
located in the cerebellum, not the cortex.
• During conditioning, changes occur in the
lateral interpositus nucleus (LIP) of the
cerebellum
– Responses increase as learning proceeds
– necessary for learning and retention
• However, a change in a brain area does not
necessarily mean that learning took place in
that area.
Learning, Memory, Amnesia, and Brain
Functioning
• Suppression of activity in 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.
• But suppression of the red nucleus also led to
a similar condition.
• Later assumed that the learning did occur in
the LIP, as it was the last structure that
needed to be awake for learning to occur.
Learning, Memory, Amnesia, and Brain
Functioning
• Psychologist differentiate between learning
and memory.
• Hebb (1949) differentiated between two types
of memory:
• Short-term memory – memory of events
that have just occurred.
• Long-term memory – memory of events
from times further back.
Learning, Memory, Amnesia, and Brain
Functioning
• Differences between STM and LTM
– Short-term memory has a limited capacity;
long-term memory does not.
– Short-term memory fades quickly without
rehearsal; long-term memories persist.
– Memories from long-term memory can be
stimulated with a cue/ hint; retrieval of
memories lost from STM do not benefit
from the presence of a cue.
Learning, Memory, Amnesia, and Brain
Functioning
• Researchers propose all information enters
STM where the brain consolidates it into LTM.
• Later research has weakened the distinction
between STM and LTM
• Working Memory
– Proposed by Baddeley & Hitch 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.
Learning, Memory, Amnesia, and Brain
Functioning
• Common test of working memory is the
delayed response task.
– Requires responding to something you
heard or saw a short while ago.
• Research points to the prefrontal cortex for
the storage of this information
• Brain may use elevated levels of calcium to
potentiate later responses
Learning, Memory, Amnesia, and Brain
Functioning
• 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, Amnesia, and Brain
Functioning
• Amnesia is the loss of memory.
• Studies on amnesia help to clarify the
distinctions between and among 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, Amnesia, and Brain
Functioning
• H.M. is a famous case study in psychology
who had his hippocampus removed to
prevent epileptic seizures.
• Afterwards H.M. 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, Amnesia, and Brain
Functioning
• H.M. 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
• Retrograde amnesia – the loss of
memory events prior to the occurrence
of the brain damage.
Learning, Memory, Amnesia, and Brain
Functioning
• Patient 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, Amnesia, and Brain
Functioning
• H.M. had difficulty with episodic memory and
declarative memory.
– Episodic memory: ability to recall single
events.
– Declarative memory: ability to state a
memory into words.
• H.M.’s procedural memory remained intact.
– Procedural memory: ability to develop
motor skills (remembering or learning how
to do things).
Learning, Memory, Amnesia, and Brain
Functioning
•
Research of the function of the
hippocampus suggests the following:
1. The hippocampus is critical for
declarative memory functioning
(especially episodic).
2. The hippocampus is especially important
for spatial memory.
3. The hippocampus is especially important
for configural learning and binding.
Learning, Memory, Amnesia, and Brain
Functioning
• 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, Amnesia, and Brain
Functioning
• Damage to the hippocampus also 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 water maze task – a rat must
swim through murky water to find a rest
platform just underneath the surface.
Learning, Memory, Amnesia, and Brain
Functioning
• Hippocampus may also be important for
contextual learning
• Remembering the detail and context of an
event
• suggests that the hippocampus is important
in the process of “consolidation”.
• 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, Amnesia, and Brain
Functioning
• Reverberating circuits of neuronal activity
were thought to be the mechanisms of
consolidation.
• Consolidation is also 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, Amnesia, and Brain
Functioning
•
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, Amnesia, and Brain
Functioning
• Korsakoff’s syndrome – brain damage
caused by prolonged thiamine (vitamin B1)
deficiency
• impedes the ability of the brain to
metabolize glucose.
• Leads to a loss of 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, Amnesia, and Brain
Functioning
• 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, Amnesia, and Brain
Functioning
• 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, Amnesia, and Brain
Functioning
• Accumulation of the tau protein results in:
– Plaques – structures formed from
degenerating neurons.
– Tangles – structures formed from
degenerating structures within a neuronal
body.
Learning, Memory, Amnesia, and Brain
Functioning
• A major area of damage is the basal forebrain
and treatment includes enhancing
acetylcholine activity.
• One experimental treatment includes the
stimulation of cannabinoid receptors that
limits overstimulation by glutamate.
• Research with mice suggests the possibility
of immunizing against Alzheimer’s by
stimulating the production of antibodies
against amyloid beta protein.
Learning, Memory, Amnesia, and Brain
Functioning
• Lessons from studying amnesiac patients
include:
– There can be deficiencies of very different
aspects of memory.
– There are independent kinds of memory.
– Various kinds of memory depend on
different brain areas.
Learning, Memory, Amnesia, and Brain
Functioning
• Other subcortical brain areas and the cortex
important in learning:
• Amygdala associated with fear learning
• Parietal lobe associated with piecing
information together
• anterior and inferior region of the temporal
lobe and semantic memory
– semantic dementia (loss of semantic
memory)
Learning, Memory, Amnesia, and Brain
Functioning
• Other areas of the cortex important in
learning (con’t):
• Prefrontal cortex and learning about rewards
and punishments
– Basal ganglia, anterior cingulate cortex
also involved
Storing Information in the Nervous
System
• Activity in the brain results in physical
changes.
• Patterns of activity leave a path of physical
changes.
• Not every change is a specific memory as
was once originally believed.
• Many ideas originally believed to be true have
been refined.
Storing Information in the Nervous
System
• A Hebbian synapse occurs when the
successful stimulation of a cell by an axon
leads to the enhanced ability to stimulate that
cell in the future.
– Increases in effectiveness occur because
of simultaneous activity in the presynaptic
and postsynaptic neurons.
– Such synapses may be critical for many
kinds of associative learning.
Storing Information in the Nervous
System
• Studies of how physiology relates to learning
often focus on invertebrates and try to
generalize to vertebrates.
• The aplysia is a slug-like invertebrate that is
often studied due to its large neurons.
• This allows researchers to study basic
processes such as:
– Habituation
– Sensitization
Storing Information in the Nervous
System
• Habituation is a decrease in response to a
stimulus that is presented repeatedly and
accompanied by no change in other stimuli.
– Depends upon a change in the synapse
between the sensory neurons and the
motor neurons.
– Sensory neurons fail to excite motor
neurons as they did previously.
Storing Information in the Nervous
System
• Sensitization is an increase in response to a
mild stimulus as a result to previous exposure
to more intense stimuli.
• Changes at identified synapses include:
– Serotonin released from a facilitating
neuron blocks potassium channels in the
presynaptic neuron.
– Prolonged release of transmitter from that
neuron results in prolonged sensitization.
Storing Information in the Nervous
System
• Long-term Potentiation (LTP) occurs when
one or more axons bombard a dendrite with
stimulation.
– Leaves the synapse “potentiated” for a
period of time and the neuron is more
responsive
Storing Information in the Nervous
System
• Properties of LTP that suggest it as a cellular
basis of learning and memory include:
– Specificity
– Cooperativity
– Associativity
Storing Information in the Nervous
System
– Specificity – only synapses onto a cell that
have been highly active become
strengthened.
– Cooperativity – simultaneous stimulation
by two or more axons produces LTP much
more strongly than does repeated
stimulation by a single axon.
– Associativity – pairing a weak input with a
strong input enhances later responses to a
weak input.
Storing Information in the Nervous
System
• Long-term depression (LTD) is a prolonged
decrease in response at a synapse that
occurs when axons have been active at a low
frequency.
– The opposite of LTP
Storing Information in the Nervous
System
• Biochemical mechanisms of LTP are known
to depend on changes at glutamate and
GABA primarily in the postsynaptic neuron
• This occurs at several types of receptor sites
including the ionotropic receptors:
–AMPA receptors
–NMDA receptors
Storing Information in the Nervous
System
• LTP in hippocampal neurons occurs as
follows:
– Repeated glutamate excitation of AMPA
receptors depolarizes the membrane.
– The depolarization removes magnesium
ions that had been blocking NMDA
receptors.
– Glutamate is then able to excite the NMDA
receptors, opening a channel for calcium
ions to enter the neuron.
Storing Information in the Nervous
System
– Entry of calcium through the NMDA
channel triggers further changes.
– Activation of a protein that sets in motion a
series of events occurs.
– More AMPA receptors are built and
dendritic branching is increased.
• These changes increase the later
responsiveness of the dendrite to incoming
glutamate.
Storing Information in the Nervous
System
• Changes in presynaptic neuron can also
cause LTP.
• Extensive stimulation of a postsynaptic cell
causes the release of a retrograde transmitter
that travels back to the presynaptic cell to
cause the following changes:
– Decrease in action potential threshold
– Increase neurotransmitter release of
– Expansion of the axons.
– Transmitter release from additional sites.
Storing Information in the Nervous
System
• LTP reflects increased activity by the
presynaptic neuron and increased
responsiveness by the postsynaptic neuron
• Understanding the mechanisms of changes
that enhance or impair LTP may lead to drugs
that improve or block memory.
– Increasing production of hormones
increased by LTP
– Ginkgo biloba
– Etc.