Hebbian synapse
mechanism of learning and memory
potentiation: if presynaptic cell consistently drives postsynaptic, strengthened
depression: if presynaptic cell fails to drive postsynaptic, weakened
forgetting function
illustrates how we forget info over time without reinforcing
nonlinear: rapidly at first, then levels off
repetition improves
Bliss & Lomo
first demonstration of experience-dependent plasticity proposed by Hebb
LTP
long-term potentiation
persistent strengthening of synapses
NMDA glutamate receptor
important for early stages of LTP
activated by glutamate from presynaptic cells
voltage-dependent; normally blocked by a magnesium ion
when repeatedly depolarized, magnesium ion leaves
allows calcium into cell, activating secondary-messenger systems
synaptic strengthening
long-term depression occurs with no response of the post-synaptic cell to repeated input
coincidence detector
neurogenesis
thousands of new neurons formed in hippocampus every day
younger neurons → greater plasticity
new cells → framework for establishing connection among existing
in hippocampus → important for storing information
dendritic spines
potential structural basis for long-term info storage
grow and change in hours in young
less plastic and more stable in adults
may be important for memory storage
stages of memory
encoding, storage, retrieval
encoding
first stage of memory
information transformed into storable format
acquisition and consolidation
acquisition
stimuli are captured and processed in short-term memory
consolidation
memory is stabilized into long-term memory
storage
second stage of memory
preservation of info in memory
categorized into different types
retrieval
third (final) stage of memory
process of accessing stored memory
influenced by:
strength of memory
context during encoding and retrieval
types of memory
sensory
short-term and working
long-term nondeclarative
long-term declarative
sensory memory
brief, immediate storage of sensory inputs
characteristics:
milliseconds to seconds
high capacity
no conscious awareness
lost through decay
short-term/working memory
temporary storage of information undergoing active manipulation/rehearsal
characteristics:
seconds to minutes
limited capacity (7 ± 2 items)
conscious awareness
lost through interference and decay
characteristics of long-term nondeclarative memory
minutes to years
high capacity
no conscious awareness
lost through interference
characteristics of long-term declarative memory
minutes to years
high capacity
conscious awareness
lost through interference
list learning task (serial position task)
task: listen to a list of words and report back as many as you remember
primacy and recently effects
manipulate learning and retrieval variables
# of trials, rate of presentation, length of delay, etc.
primacy effect
people tend to remember items at the beginning of a list
long-term memory
serial position task
recency effect
people tend to remember items at the end of a list
short-term memory
serial position task
disrupting recency effect
length of delay affects short-term memory
distraction after end of list eliminates recency effect
disrupts ability to hold final items in short-term memory
disrupting primacy effect
speeding up rate of word presentation reduces primacy effect
less time to encode into long-term memory
visual report task
presented with a mix of letters very briefly
can usually report 4-5 accurately
partial report:
immediately after removal, tone is played to indicate row
usually can report 3-4 correctly from a single line
modal model (Atkinson and Shiffrin multi-store model)
discrete stages of memory with different characteristics
serial progression of information through memory stages
storage
attention: sensory → short-term
rehearsal/encoding: short-term → long-term
retrieval
control processes: long-term → short-term
retrieval/recognition cues
patient KF
damage to left parisylvian cortex (parietal lobe)
short-term memory impairments
difficulty recalling information/details that he had just heard
retained ability to form long-term memories
challenge to strict serial hierarchy
patient EE
tumor in left angular gyrus and inferior parietal
short-term memory impairments
poor STM for abstract verbal and transposing numbers
normal calculating/other number processing
normal visuospatial STM and non-verbal long term
strong primacy effect, no recency effect
STM not a necessary gateway to LTM
working memory
expands on concept of short-term memory
content from recent sensory inputs
retrieval from long-term memory
conscious recall of recent events
maintenance/manipulation
maintain information through rehearsal
manipulation by central executive
popularized by Baddley & Hitch model
Baddley & Hitch model
model of working memory
PFC, ACC, parietal lobe, Broca/Wernicke, occipital lobe
PFC (Baddley & Hitch)
central executive
executive control tasks:
integrating info for decision-making
maintaining/manipulating stored info
high cognitive load tasks
updating info
ACC (Baddley & Hitch)
attention controller
evaluates need for adjustments and adaptations based on task demands
Broca/Wernicke (Baddley & Hitch)
phonological loop
left hemisphere: verbal and acoustic information
parietal cortex (Baddley & Hitch)
episodic buffer
processing “workspace” for sensory and perceptual
occipital lobe (Baddley & Hitch)
visuospatial sketchpad
right hemisphere: visual and spatial information
delayed match-to-sample task
presented with a stimulus (good/poor), delay, asked to choose the matching stimuli
requires holding information in working memory
reflects preferred stimulus of neuron
neurons in IT cortex exhibit elevated delay activity even in a sense of stimulus
reflects WM for object attributes
disrupting working memory
adding distractions during delay period
accuracy decreases with # of intervening distractors
working memory - parietal cortex
delay activity for stimulus location
working memory - PFC
reflects memory for object attributes and location
ventrolateral: patterns/object selectivity
dorsolateral: spatial selectivity
not attenuated by intervening stimuli: keeps track of behavioral goals
nondeclarative memory: procedural
learning/remembering skills and habits
automatic over time
often motor skills
not necessarily consciously available
cerebellum, basal ganglia, motor cortex
nondeclarative memory: perceptual
learning/remembering perceptual information
no conscious awareness or intention
often repeated exposure to stimuli (shapes/patterns/sounds)
influences actions and performance in perceptual skills
priming, perceptual learning, sensory adaptation
sensory cortex, occipital lobe
nondeclarative memory: classical conditioning
type of implicit long-term memory
learning and remembering associations between stimuli and responses
no conscious awareness or intention
conditioned and unconditioned responses, reflexive actions
amygdala, cerebellum
nondeclarative memory: operant conditioning
learning driven by outcomes of actions (reward/punishment)
linking specific behaviors with outcomes (BF Skinner)
basal ganglia, associated structures
nondeclarative memory: habituation
responses to a stimulus decrease with repeated exposure
ignore repetitive, non-harmful stimuli
CNS changes, not peripheral adaptation (muscle fatigue)
declarative memory: semantic
type of explicit memory that stores facts and concepts
consciously accessible, deliberate recall
hierarchically organized
general knowledge → specific information
lacks details about where fact was learned
medial temporal lobe (hippocampus)
declarative memory: episodic
type of explicit memory that stores autobiographical events or experiences
consciously accessible, subjective experience
chronologically organized
medial temporal lobe (hippocampus)
amnesia
substantial memory deficits
injury/trauma to the brain or neurodegenerative diseases
may regain over time or be permanent
anterograde amnesia
inability to form new memories
most amnesia is this type
retrograde amnesia
inability to remember events before a specific point in time
Ribot’s law
principle in neuropsychology
in cases of retrograde amnesia, memories are lost in reverse chronological order
most recent likely to be lost, older likely to be preserved
patient HM
bilateral resection of MTL and hippocampus to treat epilepsy
anterograde amnesia
inability to form new LTM
access to old memories, partial loss of recent memories
nondeclarative memory:
could learn and improve, but no memory of having done the task before
patient KC
damage to multiple brain regions, including MTL
episodic amnesia (retrograde/anterograde):
semantic (facts) memory intact, slow acquisition
only very early episodic memory
patient Clive Wearing
extensive damage to hippocampus and surrounding
anterograde/retrograde amnesia
only sporadic recollection of past life
could play piano and conduct, but not remember having done so
near-continuous state of reawakening to the present moment
Korsakoff’s Syndrome
thiamin deficiency due to poor nutrition, chronic alcoholism
confusion, disorientation, confabulations, apathy
anterograde and retrograde amnesia
more severe than MTL or dorsomedial thalamus lesions
mammillary bodies, thalamus
patient PZ
Korsakoff’s amnesia
wrote autobiography prior to amnesia - “ground truth”
early recollection more accurate than late (pre-amnesia)
clear temporal gradient (Ribot’s law)
Alzheimer’s disease
progressive, irreversible neurological disorder, causes dementia
plaques and tangles in hippocampus leading to deter nation
stages of disease:
early: difficulty with recent events, conversations, names
advancing: recent and known individuals and places
disrupts connectivity between hippocampus and PFC
chronic stress
damage to brain cells, reduced hippocampus size
dentaste gyrus and CA1 particularly affected due to high density of cortisol receptors
impaired memory formation, forgetfulness, learning difficulties
inhibited neurogenesis, dendritic hypotrophy
interference with sleep quality
Patient S
could not forget: could repeat hundreds of words/numbers
inflexible memory
trouble discerning importance, extracting gist, following plot, understanding poetry/art/metaphors
difficulty with faces (changing)
unable to generalize
Patient MS
right occipital lobe removed due to epilepsy
preserved explicit memory: intact recall and recognition
impaired implicit memory: impaired visual priming
declarative theory (hippocampus)
theory of hippocampal function
crucial for all forms of consciously recalled memory
episodic, semantic
recollection, familiarity
multiple-trace theory (hippocampus)
theory of hippocampal function
each time a memory is recalled, hippocampus creates a new trace or representation of the memory
dual-process theory (hippocampus)
theory of hippocampal function
retrieval contingent on two independent processes:
familiarity (oldness)
recollection (events and context)
relational theory (hippocampus)
theory of hippocampal function
representations of associations linking elements of experience or knowledge to construct cohesive memory
cognitive map theory (hippocampus)
theory of hippocampal function
constructs/maintains cognitive maps
spatial representation of environment
navigation and spatial memory
consolidation
process of stabilizing memories
days to weeks to years
MTL essential for early consolidation and storage of episodic/semantic
over time, memories re-encoded in cortex (immune to hippocampal damage)
neural basis of consolidation
representations of an event throughout cortex → MTL, bound by hippocampus
retrieval of info slowly transferred to neocortex
consolidation after repeated reactivación of the memory to create direct connections within cortex
no longer require hippocampus
long-term memories require many iterations of activation, consolidation, reactivation, reconsolidation