5/28- Limbic System

Question 1

What is the most common type of epilepsy?

Answer 1

Medial temporal lobe seizure

Question 2

Flowchart outlining fit of limbic system into the rest of the brain?

Answer 2

Input from:

• Cerebral cortex (sensory)
• Reticular formation

Outputs to:

• Cerebral cortex (association and motor)
• Hypothalamus

Basically tells you what’s most important with everything coming into the brain

Question 3

Where is the limbic system (broadly)?

Answer 3

Top/middle of prefrontal brain

Question 4

Major limbic system components and their functions (one word/phrase)?

Answer 4

Prefrontal cortex: conscience

Basal forebrain: relay system (like thalamus for rest of nervous system)

Hippocampus: memory center

Amygdala: emotions/fear

Question 5

Large connections between limbic system components (what they are and what they connect)?

Answer 5

Uncinate fasciculus: medial and temporal lobes

Cingulate fasiculus: temporal and frontal lobes (via cingulate gyrus)

Medial forebrain bundle: many connections to hypothalamus

Question 6

What is the prefrontal cortex (PFC)- characteristics/job?

Connects to what via what?

Answer 6

• Large relative size in humans compared to other primates/mammals
• Emotional parts: orbitofrontal and ventromedial cortex (dorsolateral is more rational thought)
• “Conscience”- powerful inhibition of lower hypothalamic-mediated aggression (superego)
• Connected via the uncinate fasciculus to medial temporal structures

Ex) Prefrontal lobotomy effects

Ex) Phineas Gage

Question 7

Why was the prefrontal lobotomy performed? Effects?

Answer 7

• Wide variety of conditions from schizophrenia to chronic pain syndromes

(“Ice-pick lobotomy” also became popular through orbitofrontal cortex)

• Resulted in emotionally-stunted individuals; couldn’t express emotion

(Replaced by anti-psychotic medications)

Question 8

What happened to Phineas Gage?

Answer 8

• Knocked out his orbitofrontal cortex with a tamping rod through his cheek/eye
• Remained conscious, but significant change in personality
• Became rude, very disinhibited, couldn’t hold a job (not inhibiting lower functions of hypothalamus)

Question 9

Nuclei in basal forebrain?

Answer 9

• Nucleus accumbens
• Substantia innominata (involves basal nucleus of Meynert)
• Septal area (near septum pallucidum)
• Diagonal band of Broca

Question 10

More posterior nuclei in basal forebrain?

Answer 10

• Septal area continued
• Stria terminalis and bed nuclei
• Diagonal band of Broca (now separated by anterior commissure)

Question 11

Septal area connects most to what?

Answer 11

Septal area has many hippocampal connections

Afferent fibers: from hippocampus to medial/lateral septal areas

Efferent fibers: to diagonal band of Broca to hippocampus and back

Question 12

Other septal area connections?

Answer 12

• To prefrontal cortex

Via medial forebrain bundle:

• To hypothalamus
• To mammillary bodies
• To medial thalamus

Question 13

Function of septal area?

Answer 13

• Relay station between hippocampus and hypothalamus
• Modulates function of both of these
• Electrical stimulation modulates aggressive behavior and elicits drinking behavior
• Lesions cause “septal rage” (uninhibited lower structures/hypothalamus)

Question 14

Nucleus accumbens connections?

Answer 14

Afferent: receives large dopaminergic projection from ventrotegmental area (VTA) in the mesolimbic pathway

Efferent:

• Projections back to VTA
• Substantia innominata
• Substantia nigra

Question 15

Functions of nucleus accumbens?

Answer 15

• Integrates sequencing of motor responses associated with emotion and rewards
• Implicated in addiction (e.g. cocaine induces release of dopamine into this region)

– e.g. mice would hit reward level over food, reproduction, etc…

Question 16

What is the substantia innominata? Connections?

Answer 16

Aka “perforated substance” b/c many blood vessels

• Relay nucleus form amygdala to lateral hypothalamus
• Also contains Nucleus Basalis of Meynert
• Cholinergic nucleus that projects to widespread areas of cortex and limbic system

Question 17

Functions of substantia innominata?

Answer 17

• Arousal and memory

(Loss in Alzheimer’s disease and some in Parkinson’s)

Question 18

Where is the hippocampal formation located?

Answer 18

Temporal lobe

Question 19

Three divisions of the hippocampal formation?

Answer 19

• Subicular cortex/subiculum
• Hippocampus (CA regions, esp CA3 and CA1)- Archicortex
• Dentate gyrus (mossy fiber cells as opposed to pyramidal)

Question 20

Two basic pathways in hippocampus

Answer 20

Both enter via entorrhinal cortex:

• Perforant pathway- through subiculum to dentate gyrus (projections back to CA 3 and 1 and back out entorrhinal path)
• Alvear pathway- forms fornix going to other regions of limbic system and cortex

Question 21

What are the Schaffer collaterals?

Answer 21

Connection between CA3 and CA1 region; underly memory

Question 22

What process sets memory storage?

Answer 22

Long term potentiation (e.g. CA3 input to CA1 neuron)

• Brief high frequency stimulation results in strong and long term potention of an otherwise weak signal
• Input without tetanus will not receive LTP

Question 23

Biochemical process at play in long term potentiation (LTP)?

Answer 23

• Strong depolarization removes Mg2+ ion block of the NMDA receptor
• Glutamate binds and allows Ca to enter the post-synaptic neuron
• Ca acts as a 2nd messenger to activate kinases which can potentiate existing AMPA receptors and recruit new AMPA receptors to the synapse

Question 24

What is the Papez Circuit?

Answer 24

• Efferent projections from hippocampus through fornix to post-commissural fornix down to mammillary bodies
• Mamillary bodies send projections through mammillothalamic tract to anterior nucleus of thalamus
• Ant. nucleus of thalamus sends projections to cingulate gyrus
• Then from cingulate gyrus back through entorrhinal cortex back to hippocampus

Mnemonic: “He Man Ate a Cat”

Question 25

Amygdala anterior or posterior to hippocampus?

Answer 25

Anterior

Question 26

What nuclei are comprised within the amygdala?

Answer 26

- Corticomedial group - Basolateral group

Question 27

The amygdala receives information from what?

Answer 27

- **Olfactory bulb** (\*directly) - **Diffuse sensory cortices** - **Basal forebrain structures** - **Medial thalamus and hypothalamus** Can integrate much information in emotional context before passing on to lower structures

Question 28

Efferent projections of the amygdala?

Answer 28

- **Corticomedial** group to the **medial hypothalamus** via **stria terminalis** (directly or via bed nuclei) - **Basolateral** group to the **lateral hypothalamus** (and also PAG, and prefrontal cortex) via **ventral amygdalofugal** path

Question 29

Functions of amygdala?

Answer 29

- Functions via potent **control** over the **visceral processes of the hypothalamus** - Plays a role in **regulating aggression/rage, feeding, cardivoascular, and endocrine functions**

Question 30

What is the **Kluver-Bucy Syndrome**?

Answer 30

Often seen in lesions/strokes of amygdala, will see some (but normally not all) of the following symptoms first seen in monkeys with lesioned amygdalas: ## Footnote **- Hypersexuality** **- Erratic feeding** **- Loss of fear response** **- Inappropriate oral exploratory behavior**

Question 31

What did the **Little Albert experiment** show?

Answer 31

**Conditioned fear** (how environment is more important than genetics and can change personality) - PROVES THAT **FEARS ARE LEARNED** - Not originally afraid of white rate, but becomes scared when accompanied by loud clanging (fear spreads also to rabbit and all furry things) - **Unconditioned** stimulus: clanging bell - **Conditioned** stimulus: white rat (This same principle is also at play in **conditioning therapy**- pairing pleasant stimuli with things that people fear to get them over it)

Question 32

What controls conditioned fear? 2 different pathways?

Answer 32

**The amygdala** - **Direct route**: through **thalamus** (never appears through conscious mind) - **Indirect** **route**: through **cortex** (through **occipital** cortex through **associated cortices** back to amygdala)

Question 33

What is not required for conditioned fear? Exception?

Answer 33

**The hippocampus is not required for conditioned fear**, except in regard to **contextual fear** (e.g. the lab room in Little Albert's experiment)

Question 34

What is the role of monamine nuclei?

Answer 34

Collectively control **conscious state and mood** (among other things) (e.g. mood and arousal may affect fear and emotional response)

Question 35

Monoamine nuclei include what and project where?

Answer 35

Widely throughout forebrain, including the limbic forebrain: - **VTA** -\> **dopamine** (mesocortical pathway) - **Locus ceruleus** -\> **NE** (project bilaterally in brain)-- **attention** to stimulus - Midline **raphe nuclei** -\> **serotonin-- mood** - **Nucleus basalis (of Meynert)** -\> **ACh**-- **arousal and memory**

Question 36

Medial temporal lobe seizure symptoms (categorized by component of limbic system)?

Answer 36

_Amygdala:_ - Fear - Bad smell _Hippocampus:_ - Deja vu (familiarity in unfamiliar place) - Jamais vu (unfamiliarity in familiar place) - Amnesia _Basal forebrain nuclei:_ - Increased heart rate (via hypothalamic connections) - Increased blood pressure (via hypothalamic connections) - Altered consciousness - Laughing (hypothalamus) - Spitting _Prefrontal cortex:_ - Automatic behaviors (lip smacking, picking...) - Post-ictal confusion/psychosis

Question 37

What is most common cause of inappropriate/unstimulated laughing/laughing seizure?

Answer 37

Hamartoma in the hypothalamus (don't feel happy while laughing)