Limbic system and learning/memory Flashcards
Why did patient HM have memory deficits?
He had his hippocampus, perirhinal cortex, and amygdala removed
Declarative memory
ability to recollect events or facts that have a specific temporal and spatial context as well as semantic knowledge
Where is declarative memory formed and consolidated?
Hippocampus
Where is declarative memory stored?
Neocortex. Important in storage of faces
Procedural memory
ability to learn new motor skills
What structures process procedural memory?
cerebellum, striatum, frontal cortex
What area of brain is activated during face recognition tasks?
inferotemporal cortex
Short-term memory
memory lasting fractions of a second to seconds. Sensory systems –> sensory cortex
Working memory
Memory lasting from seconds to minutes. Dorsolateral prefrontal cortex
Lesion in dorsolateral prefrontal cortex
forgetting things like where you left your keys; executive dysfunction; confabulation
Long term memory
lasts days to years. Stored in neocortex
Input pathway to hippocampus
entorhinal cortex via perforant path –> dentate gyrus –> mossy fibers –> CA3 on Ammon’s horn –> Schaeffer collaterals –> CA1
Output from hippocampus
CA3 and CA1 –> fornix
How is LTP induced in hippocampus?
repeated stimulation of:
perforant path –> CA3
or
Schaeffer collaterals –> CA1
Molecular basis for LTP
simultaneous glutamate excitation and postsynaptic depolarization –> NMDA activation –> Ca influx –> Calmodulin stimulation –> CaM kinase II stimulation –> autophosphorylation of CaM Kinase II –> prolonged activity –> larger EPSP, incorporated and phosphorylated AMPA receptors –> increased glutamate response
associative memory
learning to associate several cues with a particular fact or object. Active while playing charades. Induced by LTP
learning
synapse formation/retraction in somatosensory cortex. neurogenesis in olfactory bulb, hippocampus and cerebellum
Alzheimer’s disease amyloid hypothesis
A-beta 42 –> synapse loss and neurodegeneration –> cognitive impairment
APP proteolysis by beta and gamma secretases –> A-beta –> neurotoxicity –> failure to maintain LTP in hippocampus
Alzheimer’s therapy based on amyloid hypothesis
reduce A-beta levels in brain of early AD patients
A-beta antibodies; inhibition of B/y secretase proteases –> blocked APP proteolysis
Role of amygdala in emotion
4 F’s: Flight, fight, food, sex
removal –> Kuver-Bucy syndrome
“Emotional” limbic system
Amygdala, Cingulate gyrus, DM of thalamus, ventral basal ganglia (caudate and putamen), insular cortex, hypothalamus
Where is emotion expressed and encoded?
expressed: hypothalamus and midbrain reticular formation –> autonomic visceral/somatic motor actions
Encoded: limbic system (areas around the 3rd ventricle
Conditioned flavor aversion
Associative learning
Food + malaise –> avoid that food
Does conditioned flavor aversion involve “Pavlovian” conditioning (ie: simultaneous stimulation by different stimuli)?
No! You get sick within ~30 min of eating –> robust CFA. Can happen with a single episode of malaise
Mechanism of conditioned flavor aversion
novel food –> cholinergic neuron activation in basal forebrain –> Ach release to brain –> insular cortex activity –> NMDA receptor phosphorylation (LTP) –> affected NMDA response to input from amygdala
Amygdala receives malaise info from CN X
Stimulation of amygdala + NMDA –> CFA
What drug class can prevent conditioned flavor aversion?
antimuscarinics. Block cholinergic neuron activation in basal forebrain
