Limbic System, Emotions

Question 1

Understand the difference between declarative and procedural memory.

Answer 1

Declarative memory: the 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)
• Impairment seen with hippocampal lesions.
• The hippocampus is involved in consolidation of the memory and the memory is stored in the
cerebral cortex.

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.
• Impairment seen with cerebellar, basal ganglia and frontal cortex lesions

Question 2

What kind of memory is impaired in lesions of the Hippocampus, Frontal cortex, Neocortex, and the Cerebellum/basal ganglia?

Answer 2

Hippocampus: Declarative memory

Cerebellum/basal ganglia: Procedural memory

Frontal cortex: Procedural memory

Neocortex: long term

Question 3

Understand the concepts of short-term, working and long-term memory.

Answer 3

1. Short-term memory lasts for fraction of seconds to seconds
   Ex: When grasping an object, your short-term memory allows you to remember to keep holding onto it.
   Takes place in sensory cortex
2. Working memory lasts for seconds to minutes
   Takes place in frontal lobes
   Ex: Remembering which ingredients were added when following a recipe
3. Long-term memory lasts days to years
   Takes place in the cortex
   Ex: Remembering your parents’ faces

Question 4

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

Answer 4

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

Question 5

Understand the reason for the memory deficits displayed by patient HM.

Answer 5

HM underwent brain surgery to alleviate severe epilepsy. The surgery removed a large portion of the hippocampus, as well as the entorhinal complex and amygdaloid complex bilaterally. HM’s seizures were greatly reduced, but he developed severe deficits in his ability to form new memories with a condition known as anterograde amnesia. His deficit was limited to declarative memory. He could not 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

Question 6

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

Answer 6

Associative memory involves learning to associate several cues with a particular fact or object stored in your memory. LTP strengthens associative memory by decreasing the number of cues required to make the association with the fact or object

Question 7

Under what circumstances do hippocampal synapses undergo LTP?

Answer 7

Hippocampal synapses undergo LTP with repetitive, vigorous stimulation. Only the synapses that are stimulated will undergo LTP and LTP only takes place when the stimulation is large enough to trigger depolarization in the postsynaptic cell.

Question 8

Describe the molecular basis for LTP.

Answer 8

The cells that undergo LTP are 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 and the cells soon begin to require fewer inputs for depolarization to occur.

Question 9

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

Answer 9

Recent experiments have shown that synapses in the adult brain are not static and that synapse formation/retraction is common. New data indicate that there is 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, respectively

Question 10

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

Answer 10

Cleavage of amyloid precursor protein (APP) by beta and gamma proteases yields the neurotoxic Abeta protein (sorry…to this day, I can’t find the beta symbol in Word) found in Alzeheimer’s. Mice with deposits of this protein show a failure 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

Question 11

Understand the role of the limbic system and the amygdala in emotion

Answer 11

The amygdala is involved in processing information related to emotion and relating certain stimuli to an emotion. Some of the emotion evoked in the amygdala is innate and some results from a role in 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).

Question 12

Understand the mechanism of conditioned flavor aversion.

Answer 12

Conditioned flavor aversion is an example of associative learning that does not require simultaneous presentation of associated stimuli. Conditioned flavor aversion occurs when patients receiving chemotherapy are given food, later become sick and then associate that particular food with feeling ill. The initial stimulus (the food) is presented prior to the associated stimulus (feeling ill), yet conditioning still results. The mechanism behind this is outlined below:

1. Initial exposure to food causes the release of ACh from the basal forebrain throughout the brain.
2. ACh binds MRs in the insular cortex (taste cortex)
3. 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
4. The 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.

Question 13

Understand the Anatomy of Broca’s “Great Limbic Lobe”

Answer 13

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Question 14

Recognize that “Papez’s circuit” and hypotheses about a “Limbic System” involve some structures that are, and some that are not involved in the physiology of emotion

Answer 14

Papez’s Circuit: emotion is not a function of any specific brain center but of a circuit that involves 4 basic interconnected structures, the hypothalamus w/ mamillary bodies, anterior thalamic nucleus, the cingulated gyrus, and the hippocampus.
•Cingulated cortex - determines experience of emotion
•Hypothalamus – emotional expression
•Cingulate gyrus projects to hippocampus – hippocampus projects to hypothalamus by fornix (bundles of axons). Hypothalamic impulses reach the cortex via relay in the anterior thalamic nuclei. Emotional experience in the cingulated becomes expression by indirect transmission to hypothalamus. Hypothalamic expression goes back to cingulated through thalamus anterior nucleus

Highly reciprocal organization!

Structure not involved in emotion – Hippocampus

Structure involved but not included: ventral-medial frontal lobe, amygdala, ventral striatum (nucleus accumbens), and brainstem structures like dopaminergic neurons of ventral tegmental area.

Question 15

Understand the terms “emotion”, “mood”, “cognition”, and “motivation”

Answer 15

Emotion: complex psychophysiological experience of an individual’s state of mind as interacting with biochemical and environmental influences. Can produce “automatic” responses

Mood: Affective states. While emotions have a clear focus, a mood tends to be unfocused and diffuse. Involves a tone, intensity, and a set of predictions about future experience of reward or punishment.

Cognition: a sense for the processing of information, applying knowledge, and changing preferences. It includes such processes as memory, attention, language, problem solving, and planning.

Motivation: states that bias towards specific action patterns or patterns of behavior

Question 16

Understand the roles of the amygdalae in current theories of emotion and theories of decisionmaking.

Answer 16

Amygdala: primary roles in the formation and storage of memories associated w/ emotional events. Creates associations between sensory stimuli and specific behavioral and autonomic responses.

Emotion and decision making (cognition) are linked. The amygdala critical for associating stimuli, physiologic responses, action patterns and predictions. The VMPFC and ventral striatum are critical for generating predictions about the risks and rewards associated w/ given behaviors. VTA (reward) and serotonin (punishment) signals contribute to synaptic plasticity and associative learning in the amygdala, ventral striatum, and OFC.

Question 17

Understand the roles of the ventral striatum in current theories of emotion and theories of decision making.

Answer 17

Contains the nucleus accumbens and gets reinforcing VTA neuronal projections. Projects the output back to the VMPFC.

• Critical for generating predictions about the risks and rewards associated w/ given behaviors.
• Can have synaptic plasticity and associative learning.

Question 18

Understand the roles of the ventral tegmental area in current theories of emotion and theories of decision making.

Answer 18

Is of the midbrain adjacent to the substantia nigra. VTA neuronal pathways project to the nucleus accumbens of in the ventral striatum. VTA releases dopamine in response to errors in predictions about reward.

Question 19

Understand the roles of the ventromedial prefrontal cortex in current theories of emotion and theories of decision making.

Answer 19

necessary for the prediction of consequences, but not for registering the actual consequences. Pts demonstrate inadequate inhibition of aggression, sexual behavior, anxiety, and appetitive functions and to correctly employ these behaviors in the appropriate settings.

Question 20

Composition of the hippocampus

Answer 20

The hippocampus is rolled up (like bubble tape) to form an inner layer called the dentate and an outer layer called Ammon’s horn (see image below). Ammon’s horn contains CA3 and CA1 neurons (among others). These neurons serve as the output from the hippocampus by collecting as the fornix. Mossy fibers are neurons that connect the dentate gyrus with the CA3 cells of Ammon’s horn. Schaeffer collaterals connect CA3 neurons to CA1 neurons within Ammon’s horn. The input to the hippocampus is through the perforant path from the entorhinal cortex. The entorhinal cortex receives inputs from many other areas in the cortex.