5 - Limbic System

Question 1

What is the function of the limbic system and where is it located?

Answer 1

Interconnected cortical and subcortical structures that link visceral states and emotion to cognition and behavior.

Limbic structures are interposed between the neocortex and the brainstem. (Limbis means border)

Question 2

What is integrated within the limbic system?

Answer 2

Cortical information and hypothalamic impulses. The goal of this is homeostasis (autonomic regulation), olfaction, memory, and emotion (HOME).

Question 3

What is the funciton of each area?

Answer 3

Limbic areas in green.

Higher-order (heteromodal) associated areas in pink.

Modality-specific (unimodal) association areas in yelllow.

Primary sensory and motor areas in blue.

Question 4

What is Papez’s circuit?

Answer 4

Cingulate

Hippocampus

Fornix

Anterior thalamus

Mammillary bodies

Question 5

What contribution did MacLean make to the understanding of the limbic system?

Answer 5

Coined term limbic system and incorporated Papez’s ideas into a model that hasn’t changed much since.

Expaned it to include: parts of hypothalamus, septal area, orbitofrontal cortex, nucleus accumbens, and the amygdala.

Question 6

What is considered the outer core of the limbbic system? What is the function of each region?

Answer 6

1. Cingulate cortex: rostral - emotions; caudal - visual spatial and memory
2. Orbital frontal lobe: personality, behavior control, self-awareness
3. Temporal lobe (hippocampus, parahippocampus, entorhinal cortex): memory

Question 7

What are the inner core structures of the limbic system?

Answer 7

1. Hypothalamus
2. Amygdala
3. Septum

Question 8

What part of the limbic lobe is the hypothalamus in? What is it’s function?

Answer 8

Inner core

Pleasure center, autonomic, endocrine integration, neurons project to the pituitary, maternal behaviour, BP, feeding, temperature regulation, and immune response.

Question 9

What part of the limbic system is the amygdala in? What is it’s function?

Answer 9

Inner core structure.

Preservation of self behaviors, emotion, social behavior, aggression and defense response, sexual behavior, affective significance of visual stimuli, affect of faces, and affective regulation.

Question 10

What part of the limbic system is the septum in? What is it’s function?

Answer 10

Inner core structure.

Preservation of species behaviors, sexual behavior, emotionality.

Question 11

What connects the hippocampus to the mammillary, the anterior thalamus, the septal nuclei, and the nucleus accumbans?

Answer 11

The fornix.

Question 12

What connects the mammillary bodies and the hypothalamus to the anterior thalamus, hypothalamus, and the septum?

Answer 12

The mammillothalamic tract.

Question 13

What connects the entorhinal cortex and the cingulate gyrus to the dentate, parahippocampal gyrus, hippocampus, the amygdala, and the midbrain?

Answer 13

The perforant path.

Question 14

What is the function of the fornix?

Answer 14

It’s the main projection tract connecting the hippocampus and the mammillary boy.

Question 15

What is the function of the mamillothalamic tract?

Answer 15

Originates from the mammillary bodies and terminates in the anterior and dorsal nuclei of the thalamus.

Question 16

What is the major efferent path from the limbic system?

Answer 16

The fornix: connects the hippocampus with the septum and the mammillary bodies.

Question 17

What is the major afferent path to the hippocampal formation?

Answer 17

Perforant path: connects the entorhinal cortex with the dentate gyrus

Question 18

What is the funcion of the anterior thalamic projections?

Answer 18

Connect to the orbitofrontal and anterior cingulate cortex. (green)

Question 19

What is the path of the cingulum fibers?

Answer 19

Run from the amygdala and parahippocampus to the frontal lobe/cingulate. (red)

Question 20

What is the path of the uncinate fasciculus?

Answer 20

Connects the anterior part of the temporal lobe with the orbital and polar frontal cortex. (light blue)

Question 21

What justified the concept of the limbic system being a true system?

Answer 21

1. Common psychiologic and neurochamical properties
2. Intricate anatomic and mostly reciprocal connections
3. Common behavioral associations

Question 22

What virus has specific affinity for the limbic regions? Shat are other common psycsiologic and neurochemical properties of the region?

Answer 22

Herpesvirus

Susceptible to kindling and development of suizure foci.

High density of cholinergic innervation and opiate receptors.

Question 23

What effect can herpesvirus have on the brain?

Answer 23

Herpes encephalitis in the orbito-temporal-frontal regions.

Results in severe behavioral abnormalities and memory impairment.

Question 24

What are the three overlapping functional sections of the limbic system?

Answer 24

Hippocampal and parahippocampal regions: memory and spatial orientation

Temporal-amygdala-orbitofrontal: integration of visceral sensation and emothion with semantic memory and behavior

Medial “default network”: autobiographical memory and introspection/self-directed thinking

Question 25

What occurs with Kluver-Bucy syndrome in humans?

Answer 25

Bilateral temporal lobe lesion resulting in: Increased oral activity Hypersexuality Hypermetamorphosis - attend and react to every visual stimulus and compulsively handling objects Placidity - flattended affect, lack of fear or aggression Visual agnosia - loss of recognition of simple objects Bulimia

Question 26

What can result in Human Kluver-Bucy syndrome? What do they all have in common?

Answer 26

Post-traumatic encephalopathy Herpetic viral encephalitis Anoxia Subarachnoid hemmorrhage Pick's disease or alzheimers Bitemporal infarction Focal status epilepticus All show extensive lesions involving bilateral temporal cortex and amygdala.

Question 27

What is Geschwind Syndrome? Who is it seen in?

Answer 27

Sensory limbic hyperconnection with strengthening of synaptic connections. Interictal personality in temporal lobe epilepsy.

Question 28

What are symptoms of Geschwind syndrome?

Answer 28

Increased concern with philosophical issues. Altered sexual behavior (hyposexuality) Hypergraphia: extensive writing that is typically religious or philosophical in nature Viscosity: tendency towards interpersonal stickiness or difficulty breaking off conversation

Question 29

What is the basic characteristic of people with Geschwind syndrome?

Answer 29

Progressive overinvestment of perception and thought with affective significance resulting in a bizarrely emotionalized concept of the world. Basically the opposite of Kluver-Bucy.

Question 30

What is the difference between Interictal personality and Kluver-Bucy syndrome?

Answer 30

Interictal personality - hyperconnection Kluver-bucy syndrome - disconnection

Question 31

What is the funciton of the amygdala?

Answer 31

Major role in integration of emotions, fear, and memory. Modulation and experience of emotional reactions and attributes affective significance to visual stimuli.

Question 32

What results from lesions of the amygdala? What disorder is associated the amygdala?

Answer 32

Lesions: tameness and reduced emotionality Supports classical fear conditioning and plays a role in PTSD, a disorder characterized by inability to extinguish fear memories.

Question 33

What is the amygdala critical for? What do monkeys with no amygdala do?

Answer 33

Critical for social interactions. With no amygdala monkeys become social isolates, show indiscriminate hypersexuality, and have devastating effects on maternal behavior.

Question 34

The amount of activity in the amygdala is associated with what?

Answer 34

The amount of emotional significant and degree of ambiguity of a social interaction (firing increases as emotional significant and level of ambiguity increases because you're trying to figure out what's occurring) Some cells response selectively to faces. Involved in fear conditioning.

Question 35

What results from orbital frontal lobe syndrome?

Answer 35

Disinhibitied, tactless, boastful, grandiose, restless, impulsive, inattentive, and a tendency to dress carelessly and eat gluttonously. Problems with starting, stopping, and switching. All important for behavior.

Question 36

What results from frontal lobe syndrome of the frontal/convexity or dorsolateral region?

Answer 36

Apathetic, slow, little initiative or spontaneity, responsing in an automated manner, vacant expression.

Question 37

What results from a frontal lobe syndrome in the medial frontal region?

Answer 37

Akinetic mutism, inert, speechless, with intact sleep wake cycle. Motionless, mindless, wakefullness. Loss of drug to move or speak.

Question 38

What occurs with hippocampal lesions?

Answer 38

Hippocampal lesions lead to amnestic states such that the person can no longer encode new memories and only knows their past. The hippocampus is required for acquisition of facts and events (declarative memory)

Question 39

What is Wernicke Korsakoff's Syndrome caused by? What are characteristics of this syndrome?

Answer 39

Caused by chronic alcoholism and nutritional deficiency (thiamine). Acute state ie Wernicke's encephalopathy: confusion, disorientation, oculomotor dysfunciton, and ataxia. Chronic: anterograde and temporally-graded retrograde amnesia Lesions are in mammillary bodies and thalamus.

Question 40

What results from lesions of the septal region in humans?

Answer 40

Increased sexual activity following septal damage.

Question 41

What are the brain centers for pleasure, pain, and punishment? What substances are implicated in the location of effective self-stimulation?

Answer 41

Lateral septal region Lateral hypothalamus Medial forebrain bundle Nucleus accumbens Catecholamines and dopaminergic systems implicated in self-stimualtion.

Question 42

What effect do addictive drugs have on the limbic system? What effect do heroin and cocain have on these systems?

Answer 42

The mesolimbic dopamine system is important for motivational processes. Some drugs have their effects by enhancing mesolimbic dopamine activity. Heroin increases the nruonal firing rate of dopamine cells while cocain inhibits the reuptake of dopamine.

Question 43

What are the functions of the "default mode" regions, the posterior cingulate and the anterior cingulate?

Answer 43

Posterior: visuospatial and memory functions. Anterior: hemi-attention (contralateral neglect)

Question 44

What diseases are associated with the cingulate gyrus? What part of the gingulate gyrus is associated with each?

Answer 44

1. Tourette's syndrome: anterior cingulate region 2. OCD: cingulotomy has been successful treatment 3. Chronic pain: cingulotomy are no longer bothered by pain 4. Sociopathy: sociopathic pts show blunted autonomic resposne to emotional stimuli 5. Akinetic Mutism: associated with bilateral anterior cingulate cortex lesions

Question 45

What is the function of the anterior cingulate? What can excessive amplification of emotional and motor signals lead to? What can excessive filtering of emotions and motor behavior lead to?

Answer 45

Integration of thought, motivation, and emotional with movement. Excessive amp of emotional signals: anxiety and OCD Excessive amp of motor behavior: tics impulsive behavior Excessive filtering: apathy, akinesis, mutism.