Learning and Memory

Process of acquiring new information

specific information stored in the brainability to retrieve information

experience dependent changes in structure or function

non - associative learningassociative learningprocedural/skill learningdeclarative learning

involves learning about a single stimulus that is presented once or repeated several times

decreased response to repeated representations of a stimulusslower for high intensity stimuli (louder sound)due to changes in central processing - NOT due to fatigue or adaptation

habituationdishabituationhigh intensity stimulilong term habituation

strong stimulus causes the habituated response to reemerge

longer intervals between simuli are more effective (responses last longer and the decrease is stronger)

model system for learning and memoryGill and siphon withdraw reflex - repeated touching of the siphon results in smaller response (habituation)

after habituation of touching siphon, touch head - this erases the siphon habituation, must do it again. Can be reinstituted by another set of repeated stimuli

After training, less neurotransmitter is released into the synapse resulting in less retractionShort term - less neurotransmitter releaseLong term - fewer synapses

response is greater than the baseline level because of prior stimulation

periodic touching of tail produces a consistent response that does NOT habituateapply single strong stimulus - poke or shock to tailreturn to periodic touching of tail - response is greater than baseline due to sensitization caused by strong stimulus

A stimulus activates two systems1) Stimulus response (SR) pathway - sound --> startle2) State system - activates general arousal of animal, not always fully activated, system responsible for sensitizationconsequence of the repeated presentation will reflect the sum of two competing systems

1)Changes in synaptic strength - more or less presynaptic neurotransmitter release, smaller or larger postsynaptic responses2)Changes in neural structure - more or less synapses, more or less dendrites3)Neurons - new neurons, loss of neurons

Before training - normalAfter training - more neurotransmitter release, wider synapse, or both. Formation of new synapses, rearrangement of synaptic outputLeads to increased PSP

Donald Hebb - proposed that when two neurons are repeatedly activated together, their synaptic connection will become strongerCell assemblies - ensembles of neurons - linked via hebbian synapse could store memory traces

2 receptors NMDA and AMPA. NMDA receptor is inactivated and blocked by Mg ion.

Glutamate can flow through synapse onto AMPA receptor. When AMPA receptor is activated, it depolarizes cell. This activation leads to influx of Ca ions which leads to activation of protein kinases; starts a cascade - produces retrograde messengers (NO, arachidonic acid) which enhances glutamate release. This causes more glutamate receptors to be produced, allowing even more glutamate in. Finally, this influx overruns the Mg ions, causing them to be expelled.

Thus, this opens the NMDA receptors to glutamate, allowing for even more glutamate to enter

hippocampus

Hiccocampal pathways3 pathwaysperforant pathway - subiculum to dentate gyrusmossy fiber pathway - dentate gyrus to CA3 pyrimidal cellsschaffer collaterals - CA3 pyrimidal cells to CA1 pyrimidal cells

Correlational observationssomatic intervention experiments behavioral intervention experiments

time course of LTP is similar to that of memory formation

pharmacological treatments that block LTP impair learning

show that training an animal in a memory task can induce LTP

placed in 3 different environmentsstandard condition - regular cage with other mice with food/water (SC)impoverished condition - mice placed my itself (IC)enriched condition - placed with other mice, a lot of toys and fun stuff (EC)

Animals in EC developed increased acetylcholinesterase (AChE) activity, a heavier cerebral cortex due to increased cortical thickness which is likely due to increased dendritic branching (more synapses). Promotes better learning and problem solving, aids recovery from conditions such as malnutrition, may protect against age related declines in memory.

more dendritic spines in the cortex

Birth of new neurons. occurs mainly in dentate gyrus in adult mammalscan be enhanced by exercise, environmental richness, and memory tasks

neurogenesis turned off in adults - showed impaired spatial learning but were otherwise normal