Limbic System

Question 1

The limbic system is the site where ________ information and ____________ impulses are integrated

• What are the limbic system’s general functions?

Answer 1

cortical information and hypothalamic impulses

• HOME
  
  • ​Homeostasis (autonomic regulation)
  • Olfaction
  • Memory
  • Emotion

Question 2

Papez’s “circuit”:

Answer 2

cingulate ⇒ hippocampus ⇒ fornix ⇒
mammillary bodies ⇒ anterior thalamus ⇒ cingulate

• emotion was a product of the limbic circuit
• Input is elaborated as emotion and ultimately influence the hypothalamus to release appropriate hormones

Question 3

D. McClean coined the term “limbic system” and included which structures in it?

Answer 3

Expanded Papez’s circuit to include:

1. parts of the hypothalamus
2. septal area
3. orbitofrontal cortex
4. nucleus accumbens (part of the striatum)
5. amygdala

Question 4

What Justifies the Concept of the Limbic System?

Answer 4

1. Common physiologic and neurochemical properties
2. Intricate anatomic connections
3. Common behavioral associations

Question 5

Limibic System:

Common physiologic and neurochemical properties

Answer 5

• High density of cholinergic innervation and opiate receptors
  
  • memory
  • perception of pain and pleasure
• Septal nuclei and nucleus basalis of Meynert:
  
  • cholinergic input for the brain (memory)
• Mesocorticolimbic Dopamine system:
  
  • critical for positive reinforcing brain mechanisms
    
    • drugs and pleasure

Question 6

What are the limbic structures susceptible to?

Answer 6

1. herpes virus has a special affinity for these regions
   
   • leads to severe memory and behavioral disturbance
2. susceptible to kindling and development of seizure foci

Question 7

What does the hypothalamus coordinate?

Answer 7

drive-related behaviors

Question 8

What are the Cortical Structures in the Outer Core?

Answer 8

1. cingulate gyrus
2. orbital frontal lobe
3. subcallosal area
4. parts of temporal lobe
   
   • hippocampus
   • parahippocampal gyrus
   • uncus

Question 9

Outer Core-Cortical Components:

• Cingulate cortex:
• Orbital Frontal lobe:
• Temporal lobe:

Answer 9

• Cingulate cortex
  
  • **rostral **⇒ emotions and motor
  • **caudal **⇒ visual spatial and memory
• Orbital Frontal lobe
  
  • personality, behavioral control, and self awareness
• **Temporal lobe **
  
  • memory
  • hippocampus, parahippocampus, entorhinal cortex

Question 10

Inner Core Structures:

Answer 10

• Hypothalamic nuclei
• Anterior thalamic nucleus
• Mammillary body
• Septal nuclei

Question 11

Inner Core: Subcortical Components

Hypothalamus

Answer 11

Hypothalamus

1. pleasure center, autonomic, endocrine integration
2. neurons project to the pituitary ⇒ regulate ACTH and TSH secretion
3. involved in maternal behavior, blood pressure, feeding, temperature regulation and immune response

Question 12

Inner Core: Subcortical Components

Amygdala

Answer 12

Amygdala

1. “preservation of self” behaviors
2. emotion
3. social behavior
4. aggression and defense response
5. sexual behavior
6. affective significance of visual stimuli
7. affect of faces
8. affective regulation

Question 13

Inner Core: Subcortical Components

Septum

Answer 13

Septum

1. “preservation of species” behaviors
2. sexual behavior
3. emotionality

Question 14

Most anatomical connections are __________.

Answer 14

reciprocal

Question 15

Efferent fiber bundles of the limbic system (3):

Answer 15

1. Fornix:
   
   • connects hippocampus with septum and mamillary bodies
2. Stria terminalis:
   
   • connects amygdala with septum, hypothal, bed nuc, and nuc acc
3. Ventral amygdalofugal pathway:
   
   • connects amygdala with hypothal, brainstem, septum

Question 16

1. What is the major efferent pathway of the limbic system?
2. What is the major afferent pathway of the limbic system?

Answer 16

1. Efferent:
   
   • ​​Fornix connects hippocampus with septum and mammillary bodies
2. Afferent
   
   • ​​Perforant path connects entorhinal cortex with dentate gyrus
   • major afferent to the hippocampal formation

Question 17

Medial forebrain bundle:

Answer 17

connects hypothalamic nuclei and amygdala and brainstem nuclei

Question 18

Kluver-Bucy Syndrome in rhesus monkeys:

Answer 18

bilateral large temporal lobe lesions including amygdala, hippocampus, uncus

1. Psychic blindness - lost ability to detect the meaning of objects based on visual criteria
2. Oral tendencies - examine all objects by mouth
3. Hypermetamorphosis – notice and react to every visual stimulus
4. Tameness – no motor or vocal reactions with fear or anger
5. Hypersexuality

Question 19

Human Kluver-Bucy Syndrome:

Answer 19

1. Increased oral activity
   
   • examine objects with mouth
2. Hypersexuality
   
   • indiscriminate sexual advances
3. Hypermetamorphosis
   
   • attend and react to every visual stimulus within the visual field
   • subsequent compulsive handling of the object
4. Placidity
   
   • ​​flattened affect, lack of aggressive behavior, absence of fear
5. Visual agnosia
   
   • ​​loss of recognition of simple, familiar objects (e.g., eating utensils) or people
6. Bulimia

Question 20

Etiology of Human Kluver-Bucy Syndrome:

Answer 20

All autopsied cases have extensive lesions involving bilateral temporal cortex and amygdala

1. Post traumatic encephalopathy
2. Herpetic viral encephalitis
   
   • probably the most common
3. Anoxia
4. Subarachnoid hemorrhage
5. Pick’s disease
6. Alzheimer’s disease
7. Bilateral temporal infarction
8. Focal status epilepticus

Question 21

Geschwind syndrome:

Answer 21

sensory limbic hyperconnection-strengthening of synaptic connections

• Increased concern
  
  • philosophical, cosmic, or religious issues
• Altered sexual behavior (usually Hyposexuality)
• Hypergraphia
  
  • ​extensive writing that is typically religious or philosophical in nature
• Viscosity
  
  • ​a tendency towards interpersonal stickiness, difficulty in breaking off conversation
• progressive overinvestment of perception and thought with affective significance ⇒ bizarrely emotionalized concept of the world

Question 22

1. Geschwind syndrome (or Interictal personality) is caused by what?
2. Kluver-bucy syndrome is caused by what?

Answer 22

1. Geschwind Syndrome ⇒ Hyperconnection
2. Kulver-bucy Syndrome ⇒ Disconnection

Question 23

Brain Pleasure Regions:

Answer 23

1. Lateral septal region
2. Portions of amygdala
3. Parts of hippocampus:
   
   • Lateral hypothalamus
   • Medial forebrain bundle
   • Nucleus accumbens
4. Anterior cingulate cortex

Question 24

What is most important for motivational processes and what drugs affect this region of the brain?

Answer 24

Mesolimbic dopamine system

1. Heroin increases the neuronal firing rate of dopamine cells
2. Cocaine inhibits the reuptake of dopamine

Question 25

**What is the function of the amygdala?**

Answer 25

**Modulation and experience of emotional reactions** * thought to play a major role in the **integration of emotions, fear, and memory** * primates and humans have cells in the amygdala that **respond selectively to faces** * Amydala is critical for **normal social interactions**

Question 26

**What will happen if the amygdala is lesioned?**

Answer 26

* **tameness or reduced emotionality** * most frequently associated with affective phenomena in patients with epilepsy * support classical **fear** conditioning and plays a role in PTSD * inability to extinguish fear memories * indiscriminate **hypersexuality** * devastating effect on **maternal behavior**

Question 27

**Septal Region:**

Answer 27

1. **Sexual behavior** * **​​Septal lesions** * enhancement of social contacts * hypersexuality 2. **Emotionality** * **​**​**Septal lesions** * **​**rage-like attacks * increased irritability

Question 28

**Hippocampus:**

Answer 28

**declarative memory** * Crucial for the formation of **episodic memories** in humans * acquisition of facts and events * **Lesions** in hippocampus, dorsal medial nucleus of the thalamus, mammillary nuclei alone or in combination can lead to **amnestic states**

Question 29

**What are the two types of declarative memory?**

Answer 29

1. **Episodic:** * **Personal events** in one’s life, **actively remembered**, embedded in time and place * Ex: yesterday I went to a baseball game 2. **Semantic:** * **Facts**, known rather than actively remembered * Ex: Madrid is the capital of Spain, the square root of 9 is 3

Question 30

**Hippocampal Formation:** 1. Major **efferent** is the \_\_\_\_\_\_\_\_\_. 2. Major **afferent** is the \_\_\_\_\_\_\_\_\_.

Answer 30

1. Major **efferent** is the **fornix** 2. Major **afferent** is the **perforant path**

Question 31

Perforant path connects _________ \_\_\_\_\_\_\_\_\_ with the \_\_\_\_\_\_\_.

Answer 31

Perforant path connects **entorhinal complex (EC)** with the **dentate** 1. Neurons from EC project to dentate ⇒ synapse with granule cells and then with hippocampal pyramidal cells 2. These cells extend toward lateral ventricle where they form the alveus, then fimbria, then fornix

Question 32

Other causes of Memory Disorders (4):

Answer 32

1. Head Trauma 2. Stroke 3. Wernicke Korsakoffs 4. Dementia

Question 33

**Wernicke Korsakoff’s Syndrome:**

Answer 33

* Due to **chronic alcoholism** and nutritional deficiency **(thiamine)** * Acute state is **Wernicke's encephalopathy:** * confusion, disorientation, oculomotor dysfunction, ataxia * **Chronic anterograde and temporally-graded retrograde amnesia** * Lesions are in **mammillary bodies and thalamus**

Question 34

What are the Functions of the Cingulate Gyrus? What will happen if it is lesioned?

Answer 34

* **Anterior cingulate:** emotion and motor functions * **Posterior cingulate:** visuospatial and memory functions **_Lesions_** * Contralateral motor neglect (attention) * **Behavioral changes** after lesions of the **anterior cingulate**

Question 35

What are the behavioral changes associated with an anterior cingulate gyrus lesion?

Answer 35

* emotional blunting, decreased motivation, disruption of mating behavior, impaired maternal-infant interactions, impatience, lowered threshold for fear or startle * Abolish conditioned emotional vocalizations, * Decreased pain * In humans: apathy, disinhibition, placidity, depression, anxiety, obsessive compulsive behaviors, heightened sexuality, bulimia

Question 36

**What is the Role of the Anterior Cingulate?**

Answer 36

**Integration of thought, motivation and emotion with movement:** 1. **Excessive amplification of emotional signals:** * anxiety * obsessive compulsive behaviors 2. **Amplification of motor behavior:** * tics * impulsive behavior 3. **Excessive filtering of emotions and motor behavior:** * Apathy * akinesis * mutism

Question 37

How is the Cingulate Gyrus Assocated with Psychopathology?

Answer 37

* Cingulotomy has been used to successfully treat **OCD** * Association with **sociopathy:** * **​**Sociopathic individuals who show blunted autonomic response to emotional stimuli * **Akinetic mutism** * **​**most commonly associated with **bilateral anterior cingulate cortex lesions**

Question 38

**Gilles de la Tourette Syndrome:**

Answer 38

* **Abnormalities in AC** is postulated because of its **role in affective vocalizations** * **Complex coordinated movement patterns** are evoked by electrical stimulation of the AC * Lesions of AC can **relieve obsessive compulsive behaviors**, an associated feature of GTS * **Reduced TS symptoms seen after disconnection of AC from thalamus**

Question 39

**Frontal Lobe Syndromes (3):**

Answer 39

1. **Orbital frontal** * disinhibited, tactless, bawdy, boastful, grandiose, restless, impulsive, inattentive, perseverative, tendency to dress carelessly dress and eat gluttonously. 2. **Frontal/convexity or dorsolateral** * apathetic, slow, demonstrating little initiative or spontaneity, responding in an automaton like manner, vacancy of expression 3. **Medial frontal** * akinetic mutism, inert, speechless, with intact sleep wake cycle, “motionless, mindless, wakefulness,” loss of drive to move or speak