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MD4001 - Physiology > The Limbic System, emotion, the hypothalamus and appetites > Flashcards

The Limbic System, emotion, the hypothalamus and appetites Flashcards

1
Q

What are the main types of sensory inputs that can be put into the cortex?

A
  • visual
  • auditory
  • feel
  • memory
  • context
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2
Q

What are the core components of the limbic system

A
  • Amygdala – emotion
  • Hippocampus (+ cortex) [H. formation] = memory
  • Limbic cortex – cingulate gyrus/insula
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3
Q

What is the function of the limbic system?

A

processes emotion and related brain activity, memories, environmental cues and state of the individual and acts on this information to maximise survival strategies

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4
Q

What are the effectors of the limbic system?

A
  • Hypothalamus
  • Brainstem structures

**drive responses

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5
Q

Describe the amygdala

A
  • Grey matter blob with central, cortico-medial and basolateral nuclei
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6
Q

What is Klüver-Bucy Syndrome and what are the common features?

A
  • Rare syndrome in humans that produces behavioural impairment
  • Associated with damage to the anterior temporal lobes
  • Common:
    • Hyperorality
    • Placidity (lack of fear)
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7
Q

What is thought to cause Klüver-Bucy Syndrome?

A
  • Herpes encephalitis
  • Trauma
  • Tumours
  • Hypoxia
  • Pick’s disease
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8
Q

What is amygdala activated by to generate an emotional response?

A
  • Electrical stimulation leads to anxiety and fear
  • Fear activates central nucleus (and bed nucleus of the stria terminalis (BST))
  • fMRI –> (fear can be due to real imagined object and is context dependent; stria terminalis connects amygdala with BST and is one of a number of connecting tracts assigned to the limbic system)
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9
Q

In what disorders are the centres of the amygdala enhanced?

A

anxiety disorders

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10
Q

Describe the inputs into the amygdala

A
  • stimulus
    • take a fast tract pathway via thalamus - doesn’t reach consciousness (e.g. subliminal short route)
    • Longer route via cerebral cortex (long route e.g. visual cortex)
  • Concept - via cerebral cortex
  • Context - via hippocampus
  • Inputs go into the lateral nucleus of the amygdala
  • Outputs from the central nucleus
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11
Q

Describe the learning aspect of the amygdala

A
  • Noise or scene associated with a fear stimulus can elicit fear
  • This extends to context such as the place or situation in which the fearful stimulus occurred
  • This learning happens in amygdala (distinct from hippocampal memory)
  • Basolateral amygdala compares incoming sensory stimuli (conditioned stimuli, CS e.g. tone, light, smell or context) to previously learned aversive stimuli (unconditioned stimulus, US, e.g. fear/pain)
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12
Q

What are the main outputs of the amygdala?

A
  • output to hypothalamus via stria terminalis
  • output to a variety of brainstem centres
    • Periaqueductal grey matter (PAG)
    • Parasympathetic (colitary nucleus, dorsal vagal nucleus)
    • Ventral tegmental area
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13
Q

Summarise the functions and actions of the amygdala

A
  • Controls emotional reactions (particularly threat/fear) via effectors (hypothalamus, brainstem through the autonomic nervous system, endocrine and motor system)
  • Emotional learning resetting according to threat level and experience (memory)
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14
Q

What is responsible for higher order functions in evaluating the survival value of an emotional response?

A

Cingulate Gyrus

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15
Q

What components form the limbic cortex?

A

Anterior (ACC) and Anterior Portion of the Middle (MCC) involved in emotions

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16
Q

What connections do the ACC and MCC have for emotion?

A
  • ACC = direct communication with amygdala, and to effectors in the brainstem (behaviour/ANS)
  • MCC = to motor cortex (movement/behaviour)
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17
Q

Describe the functioning of the anterior cingulate nucleus in encoding basic emotion

A
  • Anterior cingulate nucleus encodes basic emotions; happiness, sadness and fear and emotional memory
  • Anterior cingulate has a top down influence – works to recode the amygdala
    • Computes relevance/outcomes – drives appropriate behaviour
    • Provides conflict resolution (dorsal ACC e.g. self V non-self in threat)
    • Part of pain network – thalamus, primary somatosensory area and insula
18
Q

What are the effector pathways of the limbic cortex?

A
  • Anterior and Middle Cingulate regulate complex interaction between unpleasant cues/pain emotions and avoidance behaviours and response. Work through amygdala and firectly to brainstem/motor cortex
  • Motor reactions complex and content dependent (approach/avoidance behaviour; desire to leave the room; vocalisation: facial expression; kissing; lip puckering; pushing)
  • Specific zone for driving face muscles
  • Direct outputs from ACC to autonomic system (BS – dorsal motor nucleus of X and the nucleus of solitary tract). Also, indirect via the amygdala
19
Q

What is the primary limbic cortex and what is its function?

A

ACC (+ some MCC) - higher order processing of emotion (top down with amygdala)

  • Has reciprocal connections with the amygdala
  • Heavy direct connections to autonomic centres including brainstem (bypass amygdala)
  • Attentional system, monitors conflict and resolves it
  • Pain activates complex interaction with emotion here
  • Motivates behaviours, mediates orientation towards or away from emotional stimuli
  • Recodes value of stimulus on amygdala
20
Q

What is the function of the insula?

A
  • Works with the ACC in evaluating emotional contexts – role in empathy
  • encodes “emotional awareness”
21
Q

What is the input for the insula?

A

Visceral information including pain

**Patients with lesions have defects in awareness of other people’s pain (empathy)

22
Q

Draw a diagram highlighting the function of the amygdala along with the limbic cortex

A
23
Q

Describe PTSD in the Limbic System

A
  • Part of ACC is hypo-responsive in PTSD
  • Reduction in size of ACC
  • Amygdala becomes hyper-responsive to trauma related stimuli
  • Top down control of amygdala by ACC is therefore missing in PTSD
24
Q

Summarise the functions and actions of the cingulate gyrus

A
  • Emotion response regulation coordinated via connections with amygdala
  • Makes prediction about negative consequences resolves conflicts
  • Top down regulation “recodes” the amygdala processing/responses
  • Drives conscious responses to unpleasant experiences
  • Drives avoidance behaviours and motor such as facial expression (from MCC to motor cortex
  • Also, direct influence on limbic effectors (ANS) by-passing amygdala
  • Works with insula which provides wider context of awareness to unpleasant especially visceral stimuli (empathy; pain)
25
Q

Describe the function of the hypothalamus as an effector and regulator of the limbic system

A
  • Direct input from limbic cortex, amygdala (but also reciprocal)
  • Input from olfactory, sensory systems (pain), viscera, retina, internal signals
  • Outputs neuronal to brainstem, spinal cord and via hormonal control
    • Autonomic
    • Endocrine
    • Behavioural
    • Basic homestatic
26
Q

What is the role of the locus coeruleus in the limbic system?

A
  • Midbrain nucleus involved in physiological responses to panic and stress
  • Input from CG, amygdala, PAG and hypothalamus
  • Noradrenaline fibres projecting from nucleus to widespread brain structures
  • Promotes alertness and wakefulness (widespread connections)
  • Promotes anxiety + formation and retrieval of emotional memories (amygdala) - dense projections from LC to amygdala
  • Projections to hypothalamus from LC maintains arousal and also effect autonomic nervous system output
  • Projections FROM PAG selects fight or flight mode
27
Q

Describe the role of the periaqueductal grey (PAG) in the limbic system

A
  • Part of the pathway that mediates LIMBIC autonomic reactions (e.g. FEAR, PAIN, ANALGESIA) Inputs from cingulate gyrus and amygdala
  • Projects to nucleus of solitary tract, dorsal nucleus of vagus, intermediolateral column Projections from PAG to LC selects fight or flight mode
28
Q

What are the modes/pathways of the PAG?

A
  • Defensive fear network
    • Amygdala ⇒ ventrolateral PAG⇒ vagal paths (parasympathetic in freezing)
    • Amygdala/CG ⇒ dorsolateral PAG ⇒ LC and BS (fight-or-flight switching)
  • Pain network (see ascending pathways lecture)
    • Pain regulation⇒ encephalin⇒ raphe nuclei ⇒ 5HT dorsal horn ⇒ interneuron block pain paths
29
Q

Illustrate how threat response depends on context

A
  • At distance cingulate gyrus (CG) processes response through basolateral amygdala to striatum (PAG independent)
  • Close by central amygdala (CA) drives periaqueductal grey and other brainstem centres to panic mode (AS)
30
Q

What is the function of the dorsal raphe nucleus in the limbic system

A

· Midbrain nucleus projects an ascending system

· Projects to and receives from amygdala and ACC

· 5HT (serotonin) neurons

· Determines tonic limbic activity and dynamic mood state

· Also processes descending pain paths from PAG to DRN to spinal cord

31
Q

Describe the 5HT processing and predisposition to depression in normal individuals

A

o Variant polymorphism in 5HT transporter gene (5HTT)

o Diminishes transcription efficiency and expression

o May increase risk of depression (under investigation)

o Reduced communication between ACC and amygdala

o Reduced size of amygdala and increased reactivity of amygdala to emotional stimuli

32
Q

How is the 5HT processing changed in depression?

A
  • Reduced metabolism in ACC
  • Reduced size of ACC
  • Amygdala and hyperactive
  • Highest density of 5HTT in the ACC
  • –> Efficacy of 5HT inhibitor paroxetine
  • Reduced size of amygdala but inverse correlation with treatment
33
Q

What is the impact of the hippocampus on emotion?

A

indirect influence only

34
Q

How does the hippocampus work?

A
  • Combines spatio-temporal information with emotional, sensory and cognitive information –> to establish new episodic memory
35
Q

What are the functions of the hippocampus?

A

Hippocampus plays a critical role in memory formation by providing the brain with a spatiotemporal framework within which the various sensory, emotional, and cognitive components of an experience are bound together.

This framework allows the experience to be stored in such a way that it can be later retrieved as a conscious recollection of that experience.

36
Q

What are the 3 major inputs into the hippocampus?

A
  • Emotional information
  • Things
  • Places

**Object and face recognition, conceptual identiy and salience

37
Q

In what conditions is atrophy of the hippocampus found?

A
  • Alzheimer’s Disease
  • Hypertension
  • Depression
  • Epilepsy
  • Cushing’s Disease
  • Stress (PTSD)
  • Genetic Disorders
  • Chronic alcohol use
38
Q

What is the fornix?

A
  • A major output tract of the hippocampus involved in memory
39
Q

What does the fornix project to?

A
  • Fornix projects to the mammillary bodies which are connected to the anterior nucleus of the thalamus (damage to the fornix and these two structures may cause memory problems)
40
Q

Summarise the function of the hippocampus and associated cortex (hippocampal formation)

A
  • Hippocampal formation structures in temporal lobe floor of the lateral ventricle
  • Combines spatio-temporal information with emotional, sensory and cognitive information
  • Explicit episodic memory
  • Damaged in Alzheimer’s disease, genetic syndromes and chronic alcohol use

MD4001 - Physiology (11 decks)

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