L16: Limbic Systems

Question 1

The limbic lobe was once described as “le grande lobe limbique.” What did ppl use to think this was primarily involved in?

Answer 1

The “le grande lobe limbique” included cortical area forming a rim around the diencephelon on the medial surface of the brain (cinguate cortex, parahippocampal gyrus, olfactory cortex). It was thought to be primarily involved in olfaction.

Question 2

Briefly describe Papez Circuit

Answer 2

proposed a circuit:
neocortex feeds into the cingulate cortex –> hippocamus –> hypothalamus –> anterior nuclei of thalamus, back –> cingulate cortex.

neocortex = emotional coloring
cingulate cortex = emotional experience
hypothalamus = emotional expression

Question 3

What were the 2 conclusions of the Papez Circuit?

Answer 3

1. limbic system is involved in emotion
2. describes the anatomy of the limbic system

*recall; neocortex cingulate cortex –> hippocampus –> hypothalamus –> thalamus, back to cingulate cortex

Question 4

What were the results of the Kluver-Bucy Expt?

Answer 4

temporal lobes of an aggressive monkey were removed. The monkey became docile, over-ate, and ate inappropriate items, hyper-oral, and hyper-sexual.

**at the time, proved papez circuit, but later it was shown that removing/damaging the amygdala (not part of the circuit) caused these symptoms.

Question 5

List the areas of the limbic system primarily involved in emotional processing.

Answer 5

• amygdala
• anterior cingulate cortex (ACC)
• mid-cingulate cortex (MCC)
• mediodorsal nucleus of the thalamus
• prefrontal cortex

*textbooks consider hippocampus, mammilary bodies and anterior nucleus of the thalamus part of the limbic system

Question 6

Here's a list of the key limbic structures. Briefly describe their functions
1-amygdala
2-anterior cingulate cortex (ACC)
3-mid-cingulate cortex (MCC)
4-hypothalamus
5-Periaqueductal Gray (PAG)
6-Autonomic nervous system
7-Locus Coerulus (LC)
8-Dorsal raphe nucleus (DRN)

Answer 6

1 - amygdala: invests sensory experience with emotional significance (valence); most prominently involved in fear
2 - ACC: store emotional/valenced info; recode the amygdala
3- MCC: select responses (motor or mental); predict outcomes and resolve ambiguity, improvise new behaviors for new problems
4 - hypothalamus: Autonomic/hormonal control
5 - PAG: coordinate behaviors; autonomic/skeletal
6 - ANS: skeletal motor output and memory enhancement
7 - LC: secretes NE, coordinates responses; enhances storage of emotional memories
8 -DRN: secrestes 5-HT; regulates mood

Question 7

Many experiences involve both primary and secondary emotions. Define primary and secondary emotions.

Answer 7

Primary emotions: reflexive emotions (implici), linked with autonomic reflexes, fear is the most studied primary emotion
(amygdala, hypothalamus, PAG)

Secondary emotions: conscious emotion. Object & context dependent and involve conscious processing. (cortical limbic structures)

Question 8

Where can you find the amygdala?

Answer 8

In the inferior horn of the lateral ventricle, deep to the uncus in the temporal lobe.

Question 9

Does the amygdala play a role in olfactory memory?

Answer 9

Yes, olfactory stem has projections to amygdala

Question 10

Pt. S.M had Urbach-Wiethe Diesease. Describe what causes the disease & the symptoms.

Answer 10

due to mutation in ECM protein 1, pt had no amygdalas so pt could not experience fear or recognize fear in faces. S.M had no sensory or motor defects, no changes in IQ, memory or language.

Question 11

The auditory cortex has input to amygdala. Will the patient still experience fear if the auditory cortex is cut?

Answer 11

Yes, b/c amygdala gets direct input from thalamus w/o cortical processing. This is why we have “reflexive response to fear”

Question 12

When one perceives a sensory stimulus (visual, auditory, touch), info goes to amygdala & visual cortex, activating fear response. There will then be a “fight or flight” response. Memory gets encoded in amygdala & cortex. In the presence of what molecule will this memory of fear be dramatically enhanced?

Answer 12

NE secreted from Locus Coerulus

Question 13

List the 3 emotional motor outputs of amygdala.

Answer 13

Amygdala can send info to the

1) lateral hypothalamus –> PAG
2) LC –> PAG
3) PAG

Question 14

Amygdala sends emotional motor output to the PAG directly or via the LC. Stimulation of diff parts of PAG will result in different behaviors. Explain what happens when lateral parts vs ventral part of the PAG are stimulated.

Answer 14

PAG will evoke complex & fully integrated behaviors

lateral: fight response
ventral: quiescence (hyporeactivity, bradycardia)

Question 15

Amygdala & cortex can encode emotions into memory. Can the PAG do this too?

Answer 15

No, PAG has no memory. It is controlled by higher brain regions.

Question 16

What is sham rage? What can cause sham rage?

Answer 16

Sham rage is a primary emotion that is fully integrated rage w/o external control. It can be produced by stroke/tumors to hypothalamus/PAG.

Question 17

T/F: each major component of limbic systems makes a particular contribution to PAG regulation. Structures not related directly to PAG generally play a secondary role in emotions.

Answer 17

True

Question 18

Where does PAG sends its projections (list 3 places)?

Answer 18

To ANS nuclei:
1 -nucleus of the solitary tract
2 -dorsal motor nucleus of the vagus
3 -intermediolateral nucleus (IML) -sympathetic (lamina VII from T1-L2)
Then they project to Periphery to control ANS

Question 19

What does the amygdala & the limbic cortex cause hypothalamus to secrete? Which specific nuclei of the hypothalamus are being stimulated?

Answer 19

amygdala & limbic cortex drives paraventricular nucleus (PVN) of hypothalamus (NE-driven) to secrete cortisol releasing hormone (CRH) into portal veins. CRH will cause release of adrenocorticotropic hormone (ACTH) from pituitary, which will cause cortisol release from adrenal cortex. Cortisol will increase memory.

Question 20

Hypothalamus (PVN, LH, VMH) –> PAG?

Answer 20

-LH & VMH

Question 21

LC (NE) –> PAG and which section of the hypothalamus?

Answer 21

PVN, causing the secretion of cortisol to enhance memory

Question 22

There are 4 regions of cingulate gyrus, but only 2 have specific role in emotions. List them & briefly describe the functions.

Answer 22

1 - anterior cingulate cortex (ACC)

 - involved in AFFECT
 - stores long-term emotional memories
 - operates thru ANS via projections to nucleus of solitary tract & dorsal motor nucleus of the vagus

2 - mid-cingulate cortex (MCC)

- motivated behavior & response selection
- anterior part of MCC is active during fear
- operates thru spinal projections

Question 23

If you electrically stimulate MCC, what types of responses will you evoke?

Answer 23

complex skeletomotor responses (emotional relevant motor outputs like lip puckering)`

Question 24

Amygdala has reciprocal projections to the ACC. Therefore, ACC is mainly involved in emotions. In fact, around the genu of corpus callosum is selectively vunerable to what types of diseases?

Answer 24

emotional diseases (e.g. depression)

Question 25

Imaging studies show different distributions of emotional memories. Where are fear, sadness and happiness processed?

Answer 25

• fear = anterior MCC
• sadness = ventral ACC
• happiness = rostral ACC

Question 26

What does it mean that ACC has a facial region?

Answer 26

all emotions can impact facial region, which is critical for emotional awareness. Facial region of ACC will project to facial motor nucleus in pons innervating muscles of facial expression.

Question 27

LC is a key upstream & downstream coordinator. It functions to integrate limbic motor systems. Describe its functions.

Answer 27

LC is driven by input from amygdala, and is reciprocally connected with PVN of hypothalamus (secrete cortisol to enhance memory) & amygdala. It drives fight or flight response b/c secretes NE, helps consolidate emotional memories. Therefore, it plays pivotal integrative activties

Question 28

People with mood disorders (PTSD, depression). Imaging studies can see decrease glucose usage in which regions of limbic system?

Answer 28

anterior cingulate cortex, particularly at genu of corpus callosum (VENTRAL ACC)

Question 29

How does serotonin modulate depression?

Answer 29

serotonin (via dorsal raphe nuclei) is mood-altering, and binds heavily to regions in ACC.

Question 30

Studies have shown what results from having a genetic mutation in serotonin transporters?

Answer 30

Problems with serotonin transporters will cause decrease amts of serotonin. These pts appear to have shrunken ACC & amygdala and therefore, are at higher risk for depression.

Question 31

Selective serotonin reuptake inhibitors (SSRIs) are effective for treating depression. But in major depression, it may take months to work. Why?

Answer 31

• the drug will cause an increase in serotonin in synaptic clefts, which will cause autoreceptors in dorsal raphe nuclei to decrease serotonin release from pre-synpatic cleft. Therefore, there will be a balance, and no net increase in serotonin
• over time, autoreceptors in dorsal raphe nuclei will internalize & decrease & therefore give rise to higher levels of serotonin in the ACC.

Question 32

For patients with intractable depression, one can use deep brain stimulation. Where are the electrodes placed?

Answer 32

-in or near ACC or amygdala

Question 33

Two brain structures not originally proposed by Papez as important to emotional experience and expression, but now known to be important, are the _______ and the _______.

Answer 33

amygdala and prefrontal cortex

Question 34

The cingulate cortex and its outputs are commonly referred to as primary or secondary emotions?

Answer 34

Secondary emotions, which means it can vary from person to person. What makes someone happy might not make another person happy, etc.

Question 35

Which limbic structures play a role in PTSD? What provokes PTSD?

Answer 35

overconsolidation of emotional memories via the amygdala/PAG/ACC. Just a small stimuli can elicit a huge response and is mostly provoked by NE.

Question 36

Deep brain stimulation: for intractable depression. You help to “reset” the activity of the ACC/amygdala. [It is linked to reduction of 5HT autoreceptors as well]

Patients with what type of allele results in lower levels of transporter transcription and reduced 5HT uptake; this variant have a higher risk for developing depression and have shrunken ACC and amygdala?

Answer 36

s5HTT allele