The Biology of Learning and Memory

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Chapter 14

• The Biology of Learning and Memory

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Learning and Memory Definition

• Learning
• A long term change in behavior as a function of
  experiences.

• Memory
• The capacity to retain and retrieve past
  experiences.

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Types of Learning

• Habituation
• A decrease in response following repeated
  exposure to a non-threatening stimulus.
• Sensitization
• An increase in reactivity to a stimulus following
  exposure to an intense event.
• Classical (Pavlovian)Conditioning
• Occurs through associations between an
  environmental stimulus and a naturally occurring
  stimulus.
• Operant Conditioning
• Learning that occurs through rewards and
  punishments for behavior.

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Types of LearningPavlovian Conditioning

• Learning in which a neutral stimulus is paired
  with a stimulus that elicits a reflex response
  until the neutral stimulus elicits the reflex
  response by itself.
• Unconditioned stimulus (US) - A stimulus that
  involuntarily elicits a reflexive response.
• Unconditioned response (UR) - A reflexive
  reaction to an unconditioned stimulus.
• Conditioned stimulus (CS) - An initially neutral
  stimulus that eventually elicits a conditioned
  response after pairing with a US.
• Conditioned response (CR) - A learned reaction to
  a CS.

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Classical Conditioning
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Types of Learning Operant Conditioning

• Learning how to behave to obtain reinforcement
• Reinforcers - events or activities that increase
  the frequency of the behavior that precedes that
  event or activity.
• Punishers - events or activities that decrease
  the frequency of the behavior that precedes them.
• Contingency -The specified relationship between a
  behavior and its reinforcement or punishment.

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Operant Conditioning
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Models of Memory Storage and Retrieval
Atkinson-Shiffrin model

• An experience is sequentially stored in the
  sensory register, and the short-term store, and
  the long-term store.

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Models of Memory Storage and Retrieval
Baddeleys Rehearsal Systems approach

• An alternative to Atkinson-Shiffrin in which
  Baddeley argued that memories go directly from
  the sensory register to long-term storage.

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Models of Memory Storage and Retrieval Craik and
Lockhart

• Craik and Lockhart - have a theory that memories
  differ in the extent to which they have been
  processed.

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Types of Memories
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Types of Memories
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Declarative Memory

• Memory whose formation does depend on the
  hippocampal formation
• Memory that can be verbally expressed
• Episodic memory
• Semantic memory
• Spatial memory
• Slow-wave sleep facilitates consolidation of
  declarative memories

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The Anatomy of Learning and Memory Declarative
Memory

• Squire and others have identified areas of the
  brain involved in declarative memory.
• Medial temporal lobe - Hippocampus and
  surrounding cortical areas relay information to
  diencephalic areas where it is processed and
  relayed to the frontal lobe.
• Frontal lobe - Medial temporal lobe structures
  and the medial thalamus jointly may be essential
  for the formation of long-term memory
• connections between these structures and the
  frontal lobe may provide a route by which
  memories can influence behavior.

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Role of the Hippocampus

• Input from motor and sensory association cortexes
  and from subcortical regions such as basal
  ganglia and amygdala
• Through efferent connections with these regions
  modifies the memories being consolidated there,
  linking them together
• A gradual process controlled by the hippocampus
  transforms memories into long term storage in the
  frontal cortex
• Before process completes, hippocampus is
  necessary for retrieval

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Procedural Memory

• Memory whose formation does not depend on the
  hippocampal formation
• Collective term for stimulus-response,
  perceptual, and motor memory
• Non-declarative memories control behaviors
• Learning to drive, type
• REM sleep facilitates retention
• of non-declarative memories
• Ian Waterman

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Perceptual Learning

• Learning to recognize stimuli occurs when
  synaptic changes take place in the appropriate
  regions of the sensory cortex that establish new
  neural circuits
• Learning to recognize sensory stimuli
• Primary visual cortex
• Ventral stream object recognition
• Dorsal stream object location
• Other sensory information activate similar areas
  of the association cortices

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Perceptual Short-term memory

• Activates the circuits and continues after the
  stimuli disappears
• Successfully remembering short-term is a two step
  process
• Filter out irrelevant information
• Maintain relevant information
• Also in prefrontal cortex
• Manipulate and organize
• Strategies for retrieval
• Delayed matching-to-sample task
• Faces fusiform face area face blindness
• Places parahippocampal place area

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The Anatomy of Learning and Memory Procedural
Memory

• Procedural or nondeclarative memory involves the
  neocortex and neostriatum.
• Basal ganglia structures (caudate nucleus and
  putamen) needed for
• procedural learning
• Classical conditioning
• of reflexes depends
• on the cerebellum.

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(Budson Price, 2009)
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The Memory Consolidation ProcessHebbs Cell
Assemblies

• Cell assembly - A circuit of neurons that become
  active at the same time serves as the site of
  permanent memory.
• Reverberatory activity - The continued
  reactivation of a neural circuit following an
  experience.
• Reverberatory activity is followed by
  physiological changes that produce a relatively
  permanent record of the event.
• Phase sequence - interconnected cell assemblies
  all activated at the same time in order to
  control complex processes.

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Is Reverberatory Activity Essential for Memory
Storage?

• Studies have used electroconvulsive shock to
  break up the consolidation of memory.
• ECS tends to produce retrograde amnesia
  supporting the idea that reverberatory activity
  is necessary for memory consolidation.
• CS reminders have brought back memories
  apparently lost after ECS
• Therefore, forms of brain intervention affect
  memory retrieval rather than consolidation.

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The Cellular Basis of Learning and Memory

• Cellular Modification Theory the view that
  learning permanently enhances the functioning of
  existing neural circuits or establishes new
  neural connections.
• Kandels studies of learning in Aplysia
  californica indicated both habituation and
  sensitization exist in this animal.
• Normal classical conditioning occurs in Alypsia
  with a CS of a light touch to the mantle or
  siphon paired with an electric shock to the tail.

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Structural Changes and Storing Experiences

• Experience enhances Ca2 ion entry into the
  hippocampus (Lynch, 1986).
• Exposing more glutamate receptors to stimulation
  from other neurons, making the postsynaptic
  neuron more sensitive.
• This may eventually cause changes in the terminal
  button and Lynch believes this may be the
  biological basis of learning and memory.

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The Medial Temporal Lobe

• H.M. had his medial temporal lobes, including the
  hippocampus, amygdala, and surrounding cortical
  tissue, removed as a treatment for epilepsy.
• Resulted in severe anterograde amnesia
• His procedural memory is intact.

PBS Nova Aug 2009 Clive Wearing
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The Importance of the Hippocampus

• Damage to the hippocampus results in memory
  deficits

• Case of R.B.
• hippocampal damage produced profound anterograde
  amnesia
• Case of H.M. -
• memories acquired before surgery were retained
  suggesting that the hippocampus is involved in
  the storage of declarative memory but is not the
  site of storage.
• Some researchers have found episodic encoding in
  the left frontal areas and episodic retrieval in
  the right frontal regions.

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Long Term Potentiation

• A long term increase in the excitability of a
  neuron to a particular stimulus due to the
  repeated high-frequency activity of that stimulus
• A long-lasting strengthening of synapses between
  nerve cells.
• Long-term memories are thought to be based on LTP
• Without LTP, learning some skills might be
  difficult or impossible.

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Characteristics of LTP

• A brief, sensitizing stimulus is sufficient to
  produce LTP demonstrates that hippocampal
  neurons can change synaptic responsivity
  following a single event.
• LTP-changed synaptic responsivity is confined to
  a specific neural pathway.
• LTP can be produced by either a single stimulus
  or by the convergence of stimuli that
  individually would not produce LTP.
• LTP can last for days or weeks, which suggests
  that it is not just a temporary change in
  synaptic responsivity.

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Long-Term Potentiation in the Hippocampus

• Long-term potentiation is an increase in the
  amplitude and duration of EPSPs in response to
  the test stimulus.
• Three pathways involved in LTP
• Perforant fiber pathway
• Mossy fiber pathway
• Schaffer collateral fiber pathway

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Characteristics of LTP

• LTP seems to occur through modification of the
  NMDA receptor in the Perforant and Schaffer
  collateral pathways.
• This may be a basis for operant and classical
  conditioning.

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LTP and the NMDA Receptor

• In the mossy fiber pathway, glutamate binds to
  both the NMDA and non-NMDA receptors.
• LTP apparently depends not on Ca2 influx into
  the postsynaptic receptor, but on Ca2 influx
  into the presynaptic cell after the LTP-inducing
  stimulus.
• Kandel refers to this as nonassociative - the
  organism learns about the properties of a single
  stimulus.
• Habituation and sensitization are examples of
  this type of learning.

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Neuroplasticity in the Hippocampus

• Neurogenesis - helps the brain to be modified in
  adaptation to changing environmental conditions.
• Learning that involves the hippocampus results in
  new cells surviving at a higher rate.
• The cells become part of neural circuits
  established by a temporal-based learning
  experience.
• Enriched environments have been shown to increase
  the size of an animals brain, their level of
  cortical ACh, and their learning ability.
• Studies have shown enriched environments increase
  hippocampal neurogenesis, even in adult
• animals.

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The Role of the Mediodorsal Thalamus

• Mediodorsal thalamus - A brain structure
  associated with profound memory impairment.
• People with Korsakoffs syndrome often have
  atrophy of cells in the mediodorsal thalamus
  caused by a deficiency of Vitamin B1.
• Loss of declarative rather than procedural
  memory.
• Patients are unaware that they dont remember
  make up stories (confabulation) to fill in the
  gaps.
• Emotion is generally intact with medial temporal
  lobe damage but patients with mediodorsal
  thalamic damage tend to be emotionally flat and
  apathetic

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Caudate Nucleus-Putamen Memory System

• Caudate nucleus and putamen control the ability
  to develop procedural memory.

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The Amygdala and Memory

• Stimulation of the amygdala results in enhancing
  the memory of a task
• Inhibition of the amygdala results in decreasing
  the emotional arousal effects on memory.

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Alzheimers Disease

• A type of dementia characterized by progressive
  neurological degeneration and a profound
  deterioration of mental functioning.
• Early onset - before age 65
• Risk factors include familial clustering of
  cases, increasing
• age, and Down
• syndrome.

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Alzheimers Disease
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The Cellular Basis of Alzheimers Disease

• Cellular basis of AD
• Neurofibrillary tangles
• Senile plaques
• Amyloid beta protein

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Alzheimers DiseaseGenetics

• There is a link with chromosome 21
• Another gene identified is ApoE on chromosome 19
• Some people have one or two ApoE4 alleles and
  have a greater risk of having late-onset AD.
• The product of ApoE4 is not an effective
  antioxidant for amyloid beta protein as are the
  products of other alleles.
• This may indicate a need to develop more
  effective methods to increase antioxidants in the
  brains of AD patients.