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Chapter 24: Learning/Memory (Learning and Memory (Memory: RETENTION of…
Chapter 24: Learning/Memory
Learning and Memory
Learning: ACQUISITION of new information
Memory: RETENTION of learned information
Declarative (explicit) memory: hippocampus, medial temporal lobes
memory for FACTS and EVENTS
Nondeclarative (implicit) memory: striatum, cerebellum, amygdala
Procedural learning and memory: skills, habits
Associative learning and memory: classical and operant conditioning
classical conditioning: associate stimulus that evokes a measurable response with a 2nd stimulus that doesn't normally evoke this response (PAVLOV'S DOGS)
operant conditioning: associate response (motor act) with a meaningful stimulus (like food)
Priming
Non-associative learning: habituation and sensitization
habituation: learning to ignore a stimulus that lacks meaning
sensitization: learning that intensifies your response to ALL STIMULI, even ones that previously evoked no reaction
Declarative memory
Types
Working memory (prefrontal cortex)
requires repetition to hold the memory for longer than a few seconds
limited in capacity
Short term memory
memories that last on the order of HOURS
Long term memory
memories you can recall DAYS, MONTHS, or YEARS after they were originally stored
Memory consolidation: converting short-term --> long-term
Temporal lobes
Neocortex: site of LONG TERM MEMORY storage
Hippocampus: critical for formation of DECLARATIVE MEMORIES (facts and events)
Effects of medial temporal lobectomy (includes hippocampus)
PARTIAL RETROGRADE amnesia for years preceding operation
SEVERE ANTEROGRADE amnesia
working memory (prefrontal cortex) is normal but requires SUSTAINED ATTENTION
procedural memory is NORMAL (non-declarative memory)
Medial temporal lobes important for formation of DECLARATIVE memories (MEMORY CONSOLIDATION)
Amnesia: diseases and injuries can cause loss of memory and/or ability to learn
Retrograde amnesia: memory loss for events BEFORE trauma
loss of memory months or years before trauma
Anterograde amnesia: inability to form NEW memories
Spatial memory
Does posterior hippocampus have special role in SPATIAL memory?
experiments
Morris water maze: rats will quickly learn position of platform in the cloudy water
rats with hippocampal lesions do not
mutant mouse line with REDUCED KINASE ACTIVITY in CA1 (in the hippocampus)
rats with cortical (cerebrum) lesions are normal
London Taxi Driver Study: volume of posterior hippocampus INCREASES with time driving a taxi
Cells
PLACE CELLS: CA1 pyramidal neurons that are output cells for hippocampus (the COGNITIVE MAP)
fires only when rat is a particular place (place field)
or fires based on where the animal THINKS he is (visual input)
HEAD DIRECTION CELLS (located in posterior subiculum): navigation requires "map" of space and a "compass" to tell direction
fires when head is in FIXED direction with respect to surrounding environment
same direction preference in FAMILIAR and NOVEL environment
cells don't care WHERE rat is, just what DIRECTION it's pointing
neural compass that signals animal's directional heading to the navigational system
GRID CELLS: found in Medial Entorhinal Cortex (MEC)
excited at regularly spaced, multiple locations
because grid cells differ in SPACING, each place in local environment is associated with a unique COMBINATION OF ACTIVE CELLS
Neurons with access to this combined activity could signal animal's location (place cells)
neighboring cells differ in grid scale, orientation, and phase
allows animal to LOCATE ITS BODY in a cartesian-like external COORDINATE SYSTEM
Vertebrate models of learning: Synaptic plasticity in hippocampus
Anatomy
2 thin sheets of neurons folded onto each other
Dentate gyrus
Ammon's horn: CA3, CA1
Microcircuits
PERFORANT PATH
entorhinal cortex
dentate gyrus
Dentate gyrus --> CA3
SCHAFFER COLLATERAL
CA3
fornix
CA1
Schaffer collateral synapses onto CA1 neurons used to study LTP (record EPSPs in CA1 neuron)