Limbic system Flashcards
Differentiate between declarative and procedural memory
Declarative memory: ability to recollect events or facts that have specific temporal and spatial context (i.e. the ability to name the President in 2000 or remembering where you went yesterday)
Procedural memory: ability to learn new motor skills (i.e. learning to ride a bike or tracing a shape onto a mirror). The actual act of the learning may not be remembered if declarative memory is not intact, but the learned skill will remain.
Explain the concepts of short-term, working, and long-term memory and describe the kind of memory affected by lesions of the frontal cortex.
- Short-term memory lasts for fraction of seconds to seconds
b. Takes place in sensory cortex - Working memory lasts for seconds to minutes
a. Takes place in frontal lobes (prefrontal) - Long-term memory lasts days to years
a. Takes place in the neocortex
lesions of frontal cortex would affect working memory
Discuss the experimental evidence showing that the neocortex is the site for long term memory storage.
Lesion and fMRI studies demonstrate that the neocortex is the site of for long-term memory storage. When a person is shown pictures of familiar faces, fMRI shows activity of a specific region of cortex. The portion of the cortex involved in memory storage depends on the type of memory information. Facial recognition information is stored in the inferotemporal cortex. -monkey studies where lesions of frontal cortex were performed
Recognize the reason for the memory deficits displayed by patient HM.
HM underwent brain surgery to alleviate severe epilepsy. Sg removed hippocampus, entorhinal complex and amygdaloid complex b/l. he developed deficits in forming new memories (anterograde amnesia). His deficit was declarative memory. He couldn’t recall what he had done the day before, but could still be taught new things, meaning his procedural memory was intact. The deficit in HM was the result of removal of his hippocampus. The hippocampus is important for processing memories for long-term storage in the cortex.
Explain how Long Term Potentiation (LTP) can account for associative memory.
LTP: CA1 or CA3 cells and they require stimulation by Schaeffer collaterals or mossy fibers to do so. When these cells are stimulated in a vigorous, repetitive fashion by many inputs, synaptic strengthening occurs, cells soon begin to require fewer inputs for depolarization to occur. This phenomenon is explained by the presence of AMPA and NMDA receptors in the CA1 and CA3 cell membranes. Stimulation of the NMDA receptor with glutamate under depolarized conditions allows the channel to open (recall that the Mg plug is removed by the depolarization). Ca2+ enters the cell through the NMDA receptor channel, which stimulates calmodulin. Calmodulin activates CAMKII, which phosphorylates itself. This phosphorylation is long acting, lasting for days, and results in the insertion of more AMPA receptors in the cell membrane and phosphorylation of the AMPA receptors to make them more sensitive to glutamate. The final result, CA1 or CA3 cell more sensitive to activation and can be stimulated by fewer neurons or associations to illicit recall of memories.
Describe the circumstances where hippocampal synapses undergo long term potentiation (LTP).
Hippocampal synapses undergo LTP with repetitive, vigorous stimulation. Only the synapses that are stimulated will undergo LTP, LTP only takes place when the stimulation is large enough to trigger depolarization in postsynaptic cell.
Describe the molecular basis for LTP.
NMDA receptor on CA1 or CA3 cells activated by glu and cell depolarization→ Ca2+ influx→ activation of calmodulin→ activation of CAMKII→ increased insertion and sensitivity of AMPA receptors→LTP
Describe how synapse formation and adult neurogenesis are involved in learning and memory.
synapses in adult brain are not static, synapse formation/retraction is common. adult neurogenesis in the olfactory bulb, hippocampus and cerebellum. The olfactory neurons may play a role in olfactory learning and the new neurons in the hippocampus and cerebellum may be involved in declarative and procedural learning.
Discuss the amyloid hypothesis of Alzheimer’s and the implications of this hypothesis for development of new treatments for this disease.
Cleavage of (APP) by beta and gamma proteases yields the neurotoxic A beta protein. Mice with these deposits fail to maintain the long-term potentiation (LTP) required for memory in the hippocampus. Therapeutics aimed at reducing Abeta levels or decreasing beta and gamma protease activity have potential in Alzheimer’s treatment.
Describe the role of the limbic system and amygdala in emotion
amygdala: involved in processing information related to emotion, relating certain stimuli to an emotion. Some of the emotion is innate; some results from associative learning or fear conditioning. Associative learning in the amygdala can be due to two stimuli being evoked at the same time and resulting in coincidence detection (Pavlov’s dog style) or can result from associated stimuli occurring at different times (this is discussed in the next objective).
Discuss the mechanism of conditioned flavor aversion
(taste and smell), important in cancer patients
associative learning that does not require simultaneous presentation of associated stimuli. The initial stimulus (the food) is presented prior to the associated stimulus (feeling ill), yet conditioning still results.
- Initial exposure to food causes the release of ACh from the basal forebrain throughout the brain.
- ACh binds MRs in the insular cortex (taste cortex)
- ACh binding to MRs leads to phosphorylation of NMDA receptors in the insular cortex, which sensitizes these neurons to stimulation from the amygdala. This sensitization lasts for 30 minutes
- amygdala is later stimulated by feelings of malaise from the vagus nerve. Because the amygdala sends projections to the now sensitized regions of the insular cortex, associative learning occurs at the level of the insular cortex, such that the food stimulus is now associated with feelings of malaise.
discuss the kind of memory that is impaired in lesions of the hippocampus versus the cerebellum/basal ganglia.
declarative-• Impairment seen with hippocampal lesions. -The hippocampus is involved in consolidation of the memory and the memory is stored in the
cerebral cortex.
procedural-• Impairment seen with cerebellar, basal ganglia and frontal cortex lesions
neuron anatomy of hippocampus
axons from cells in dentate gyrus, that synapse on CA3 neurons are called Mossy fibers.
Schaeffer collateral originate from CA3 neurons and synapse onto CA1 neurons. output of the hippocampus is from the CA3 and CA1 neurons through the fornix (Fig 4). both CA1 and CA3 neurons undergo LTP, this is thought to be the basis for memory consolidation.
