Limbic System Flashcards
Declarative vs procedural memory
declarative memory: the ability to recollect events or facts that have a specific temporal and spatial context
procedural memory: learning new motor skills
Memory impairment in lesions of hippocampus vs cerebellum/basal ganglia
Hippocampus is important for formation of declarative memory
Cerebellum/striatum/frontal cortex are important for formation of procedural memory
long term memory storage (evidence)
-Neocortex: evidence via fMRI and lesion studies
Ex: faces=infratemporal cortex
Pt HM memory deficits/reason
- Surgery for severe epilepsy: lesions in bilateral half of rostrocaudal hippocampus and entorhinal cortex and amygdaloid complex.
- severe anterograde amnesia (no new memories, but can remember things b/f surgery)
- deficits in declarative memory and semantic knowledge
- procedural memory intact
Long Term Potentiation and associative memory
LTP in the CA3 area of the hippocampus is important for associative memory
When do hippocampal synapses undergo LTP?
LTP on hippocampal synapses:
1. only synapses that are being stimulated during tetanus undergo
LTP.
2) LTP only takes place
when the tetanic burst is large enough to cause cell depolarization
in the postsynaptic neuron
the only synapses whose
effectiveness is increased are those
that are being stimulated by release of neurotransmitter (glutamate) AND are simultaneously being depolarized postsynaptically as a
result of depolarization elicited by the large summated input elicited
by the tetanus
Molecular basis for LTP
-NMDA receptor must be stimulated by glutamate under depolarized conditions (knock out Mg) to allow Ca influx
-Ca influx stimulated calmodulin which in turn stimulates calcium/calmodulin-dependent protein kinase II (CAMKII)
-CAMKII phosphorylates itself–> prolonged activation for days.
-CAMKII activity leads to incorporation of
AMPA receptors in the postsynaptic plasma membrane and phosphorylation of AMPA
receptors making them more responsive to the neurotransmitter glutamate = leads to larger EPSP
Synapses formation and learning/memory
- synapse formation and destruction could be important for learning
- possibility of adult neurogenesis in learning (Ex: olfactory bulb neurons regen; perhaps in hippocampus (declarative) and cerebellum (procedural memory) too
Amyloid hypothesis of Alzheimer’s
-impaired ability to form new declarative memories
-amyloid β protein (Aβ), a 42 amino acid hydrophobic
protein may cause
cognitive impairment
through loss of synapses
and subsequent
neurodegeneration
-ABeta made from proteolysis of APP (cut by Beta and gamma secretases to form neurotoxic Abeta.)
- therapeutic strategies could target reducing levels of Aβ peptide in the brain of early Alzheimer’s patients
Limbic system and amygdala in emotion
- emotional limbic system involves the amygdala, the cingulate gyrus, the mediodorsal nucleus of the thalamus, the ventral basal ganglia
(ventral caudate and putamen), insular cortex and the hypothalamus
-Ex: monkeys with removed amygdala ( altered feeding, sexual behavior, not fearful) (Kluver-Bucy Syndrome)
Ex. fear conditioning in rats (changes in lateral and central nuclei of the amygdala)
Conditioned flavor aversion
-food avoidance in cancer tx is example
-associative learning where an individual
develops an aversion for a food when it is associated with malaise (feeling sick)
-getting sick and eating food are not simultaneous
-novel food–>ACh thru brain, including insular cortex (taste), muscarinic receptor involvement (–>NMDA receptor phosphorylation
- amygdala receives
information on malaise from the vagus nerve
-Leads to associative
learning that causes aversion to the food that was paired with malaise
–>ACh has a role in memory formation, then. (treatment for Alz–chol agonists/ ACHE-Is)
Short term memory
working memory
Long term memory
Short term: lasts for fraction of sec to seconds. (in sensory cortex)
Working memory: lasts for seconds to minutes (cooking for ex; frontal lobe)
Long term memory:lasts for days and years. (cortex)
Input to hippocampus
-from entorhinal cortex through bundle of axons called perforant path (which synapse onto neurons in dentate gyrus and CA3 region of Ammon’s horn)
- Also in hippocampus: 1. axons from cells in dentate gyrus that synapse on the CA3 neurons (“mossy fibers”)
2. Schaeffer collateral axons originating from CA3 neurons and synapse onto the CA1 neurons.
Output of hippocampus
-CA3 and CA1 neurons thru axons that form the fornix
CA1 and CA3 undergo longterm potentiation, thought to be basis for learning and memory.
Treatment resistant depression might be treatable with___
Deep brain stim
