limbic system

Question 1

functions of limbic system

Answer 1

HOME: homeostasis, olfaction, memory, emotion

Question 2

Declarative memory

Answer 2

Declarative memory is the ability to recollect events or facts that have a specific temporal and spatial contex (ie. I was interviewed in this docs office yesterday) and semantic knowledge (ie. new word meanings)

Question 3

Procedural memory

Answer 3

Ability to learn new motor skills

Question 4

What kind of memory is impaired in lesions of the hippocampus vs the cerebellum/basal ganglia?

Answer 4

Hippocampus is involved in formation of declarative memory. Cerebellum/ basal ganglia are involved in formation of procedural memory

Question 5

what is anterograde amnesia

Answer 5

Patient is capable of recollecting memories formed before the surgery/incident but cant recollect any facts that take place after the event

Question 6

Where are declarative memories stored long term?

Answer 6

neocortex- different kinds of memories are stored in different parts. Ie. memory for faces is stored in inferotemporal cortex

Question 7

2. Understand the concepts of short-term, working and long-term memory. What kind of memory is affected by lesions of the frontal cortex?

Answer 7

Short term: memory that lasts for fractions of a second to seconds. Most sensory systems include this type of memory. Working memory: Lasts seconds to minutes. (ie. remembering whether you added salt, or locating keys) Located in frontal lobes. Long term: lasts days and years, stored in the cortex

Question 8

3. What is the experimental evidence showing that the neocortex is the site for long term memory storage?

Answer 8

lesion and fMRI studies- fMRI shows the activity of the brain during face recognition tasks. Lesions in this same area correlate with inability to discriminate familiar faces

Question 9

anatomy of hippocampus

Answer 9

A single cell layered dentate gyrus surrounded by Ammons horn. Ammons horn contains four types of neurons, CA3 and CA1 are most important.

Question 10

Input to hippocampus

Answer 10

From entorhinal cortex through a bundle of axons called the perforant path. Perforant path axons synapse on neurons in dentate gyrus and CA3 region of Ammons horn

Question 11

pathways within the hippocampus

Answer 11

Mossy fibers from dentate gyrus synapse on CA3 neurons. Schaeffer collateral axons from CA3 synapse on CA1

Question 12

Output from hippocampus

Answer 12

From the CA3 and CA1 neurons through axons that form the fornix

Question 13

What is associative memory

Answer 13

Learning to associate several cues with a particular fact or object

Question 14

5. Understand how Long Term Potentiation (LTP) can account for associative memory.

Answer 14

Say 9 cues/synapses are initially required to remember some fact. With repeated stimulation of these synapses, they will strengthen, such that in the future only 4-5 cues/synapses might be needed to remember the fact.

Question 15

6. Under what circumstances do hippocampal synapses undergo LTP? And what specific pathways are affected

Answer 15

In the perforant pathway on CA3 neurons or Schaefer collaterals on CA1 neurons, synapses stimulated during tetanus undergo LTP and LTP only takes place when the tetanic burst is large enough to cause cell depolarization in the postsynaptic neuron. In other words, the only synapses whose effectiveness is increased are those that are being stimulated by release of neurotransmitter (glutamate) and are simultaneously being depolarized postsynaptically

Question 16

7. Describe the molecular basis for LTP.

Answer 16

NMDA receptor has a Mg blocking the opening of the channel, so it requires both binding of glutamate AND post-synaptic depolarization (which removes the Mg) to be activated. Glutamate binds NMDA receptor > channel opens > Ca influx into cell > Ca activates calmodulin >stimulation of CAMKII (Ca/calmodulin dependent protein kinase II) > CAMKII phosphorylates itself > AMPA receptors inserted in postsynaptic membrane > AMPA are phosphorylated making them more responsive to glutamate > EPSP becomes larger

Question 17

8. How could synapse formation and adult neurogenesis be involved in learning and memory?

Answer 17

Synapse formation and retraction occurs in the somatosensory cortex of the adult brain. Also, neurogenesis occurs in the olfactory bulb, and possibly the hippocampus and cerebellum in adult brains contributing to learning.

Question 18

9. Understand the amyloid hypothesis of Alzheimer’s. What are the implications of this hypothesis for development of new treatments for this disease?

Answer 18

Evidence suggests that amyloid beta protein (Ab) may cause cognitive impairment through loss of synapses and subsequent neurodegeneration. Ab is made by proteolysis of amyloid precursor protein (APP). Ab results in failure to maintain long term potentiation in hippocampus. Therapies that reduce Ab are underway: antibodies against Ab, drugs that inhibit beta and/or gamma secretases (proteases that cleave APP)

Question 19

Which parts of the limbic system play a role in emotion

Answer 19

amygdala, the cingulate gyrus, the mediodorsal nucleus of the thalamus, the ventral basal ganglia (ventral caudate and putamen), insular cortex and the hypothalamus

Question 20

Kluver-Bucy syndrome

Answer 20

damage/removal of temporal lobes (including amygdala) results in altered feeding, sexual behavior, and lack of concern for previously feared objects

Question 21

circuits involved in fear conditioning

Answer 21

aka when a neutral stimulus is paired with an aversive stimulus, simultaneously. Eventually the neutral stimulus alone will trigger fear. It is mediated by changes in the circuits in the lateral and central nuclei of the amygdala

Question 22

What is conditioned food aversion

Answer 22

Occurs during chemotherapy. When a patient eats a novel food, then gets nauseous and vomits ~1/2 hour later they develop an aversion to that food.

Question 23

How many episodes are required for contioned food aversions

Answer 23

Just one episode of Malaise! And can last for years

Question 24

11. Understand the mechanism of conditioned flavor aversion.

Answer 24

Novel food > basal forebrain neurons release Ach throughout brain > muscarinic receptors in insular cortex bind Ach leading to phosphorylation of NMDA receptor which lasts 1/2 hour > Amygdala receives info on malaise from vagus nerve > amygdala sends signals to NMDA receptors > since NMDA receptor is still phosphorylated from the novel food, associative learning causes aversion to the food that was paired with malaise

Question 25

How is deep brain stimulation being used in depression

Answer 25

For treatment resistant depression, DBS of the limbic system (subgenual cingulate white matter) may help

Question 26

What happens when the medial temporal lobe structures are resected bilaterally?

Answer 26

This would remove half of the rostrocaudal hippocampus and adjacent entorhinal cortex and amygdaloid complex. This results in severe anterograde amnesia of declarative memory. Patient will be able to recollect facts for a short time but any distraction will make him forget the fact, including forgeting people he meets. Procedural memory is intact.