The limbic system, emotion, the hypothalamus, appetites Flashcards

1
Q

Identify the core components of the limbic system, and their effectors.

A

SUBCORTICAL STRUCTURES
Core components:
-Amygdala
-Hippocampus (sometimes considered NOT to be a limbic system structure)

CEREBRAL CORTEX STRUCTURES
-Cingulate gyrus/insula

Effectors: Hypothalamus, brainstem structures, through to the autonomic nervous system, endocrine and motor system

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2
Q

State the main function of the limbic system.

A

LIMBIC SYSTEM evaluate brain activity, memories, environmental cues and state of the individual and acts on this information to maximise survival strategies

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3
Q

Is the parahippocampal gyrus a core component of the limbic system ? Why or why not ?

A

Parahippocampal gyrus not a core component of Limbic system because it feeds information in - indirect role

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4
Q

Where is the amydala located ?

A
  • Anterior temporal lobe at the tail of caudate nucleus and rostral to hippocampus
  • Grey matter blob with central, corticomedial and basolateral nuclei
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5
Q

Define Klüver-Bucy syndrome, and identify clinical features of it.

A

Damage to the anterior temporal lobes, including the amygdala. Its clinical features include:

COMMON
• Hyperorality
• Placidity (lack of fear)

RARE
• Hypersexuality
• Visual (and other sensory) agnosia
• Hypermetamorphosis - Excessive attentiveness to visual stimuli
• Memory loss
• Enhanced aggression and anger
• Seizures
• Dementia
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6
Q

Identify possible causes, and treatment of Klüver-Bucy syndrome.

A
Causes (examples):
• Herpes encephalitis 
• Trauma
• Tumours
• Hypoxia
• Pick’s disease

Treatment is symptomatic and may include the use of psychotropic medications.

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7
Q

Identify pathologies affecting the amygdala.

A

Klüver-Bucy syndrome (anterior temporal lobe lesion)

Urbach-Wiethe disease (more specific damage to amygdala)

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8
Q

Explain the underlying cause of Urbach-Wiethe disease, and identify it’s main clinical features.

A

Underlying cause: Rare recessive genetic disorder inducing calcification in both temporal lobes caused Amygdala degenerated in half the cases.

Clinical features:

  • NO fear (was held at knifepoint without panic)
  • Defects in judgement of emotions present in facial expressions, in an odour–figure association test as well as defects in remembering negative and positive emotional content of pictures

HOWEVER, memory, attention and executive functions normal.

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9
Q

What does electrical stimulation of the amygdala result in ?

A

• Electrical simulation leads to anxiety and fear

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10
Q

Which parts of the amydala are activated in fear, and anxiety respectively ?

A

• Fear activates central nucleus (and bed nucleus of the stria terminalis (BST)).
(stria terminalis is one of a number of connecting tracts assigned to the limbic system)

• Activation of these centres is enhanced in anxiety disorders

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11
Q

Identify functions of the amygdala.

A

1) Amygdala generates and is activated by fear (emotional response)
2) Amygdala can learn a modified fear response (emotional memory)
3) Stores simple codes of value (valency; good/bad) for a threat/emotional trigger
4) Emotional responses to food (Corticomedial nuclei ) (e.g. appetite responses to pleasant and unpleasant smells for example)

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12
Q

Identify the main inputs into the amygdala. Where do these inputs go ?

A

Can be extant object, imagined or contextual.
Can be from outside and “inside” the CNS

E.g.
• Stimulus -> VIEW OF SNAKE (visual)/HISS OF SNAKE (auditory pathway)
- Take a fast, non-cortical track pathway via thalamus - doesn’t reach consciousness (e.g. subliminal short route) to the amygdala (to effectors)
- Longer route via cerebral cortex (long route e.g. visual cortex) to the amygdala (to effectors)

• Concept -> IDEA OF SNAKE/MEMORY OF SNAKE Via cerebral cortex to amygdala (to effectors)

• Context -> SNAKE IN THE ROOM
Via hippocampus to amygdala (to effectors)

• INPUTS GO Into THE LATERAL NUCLEUS of AMYGDALA

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13
Q

Where in the amygdala do outputs leave from ?

A

OUTPUTS from the CENTRAL NUCLEUS

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14
Q

Explain how the amygdala can learn a modified fear response.

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)
  • Lateral nucleus responds to stimulus pairing (pairing of conditioned stimulus and unconditioned stimulus strengthens the synapse in lateral nucleus)
  • Central nucleus drives Responses via Hypothalamus Midbrain, Pons and Medulla
  • Basolateral amygdala compares incoming sensory stimuli (conditioned stimuli, CS, e.g., tone, light, smell or context) to previously learned aversive stimuli (unconditioned stimuli, US, e.g., fear/pain).
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15
Q

Describe the pathways utilised for emotional responses to food in the amygdala.

A

Input to corticomedial nuclei from olfactory bulb (taste info)

Output from corticomedial nuclei to the hypothalamus to drive a response

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16
Q

The Amygdala stores simple codes of value (valency; good/bad) for a threat/emotional trigger Is there a more refined mechanism for evaluating the survival value of the emotional response? Identify all the main components of this network.

A

YES, more conscious regulation of emotion, in Cingulate gyrus (the anterior cingulate and anterior portion of middle cingulate) (= LIMBIC CORTEX).

  • This gyrus gets inputs from hippocampus (context information), reward center, pain paths (CC is part of pain network).
  • Outputs to motor cortex (for escape behavior).
  • Also direct connections with amygdala, effectors in brain stem (behaviour/ANS) and in motor cortex (behaviour) + to primary/association cortex (sensory information) + to insula
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17
Q

What is the function of the anterior cingulate as part of the limbic cortex ? of the motor cingulate ?

A
  • Anterior cingulate encodes basic emotions (happiness, sadness, fear) + emotional memory
  • Top down function- works to recode the amygdala (often inhibitory on the amygdala, keeps it under control)
  • Computes relevance/outcomes - drives appropriate behaviour
  • Provides conflict resolution (dorsal ACC e.g. self vs non self in threat)
  • Part of pain network - thalamus, primary somatosensory area and insula

• Mid cingulate resolves conflict and regulates motor output

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18
Q

Describe the effector pathways of the limbic cortex in emotion.

A

Anterior and middle cingulate regulate complex interaction between unpleasant cues/pain emotions and avoidance behaviours and response. Work through amygdala and directly to brain stem/motor cortex.

  • Motor reactions complex and context dependent (approach/avoidance behavior, 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.
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19
Q

Which part of the cingulate cortex is considered to be primary limbic cortex ? What does this mean ?

A

ACC (+ some MCC) considered to be PRIMARY LIMBIC CORTEX
Effectively means that it:
-performs higher order processing of emotion (top down with amygdala)
-has reciprocal connections with amygdala (modifies good/bad value from amygdala)
-has heavy connections to autonomic centres
including brainstem
-is involved in attentional system, monitors conflict and resolves it
-is where pain activates complex interaction with emotion
-motivates behaviors, mediates orientation

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20
Q

Describe the role of the insula as part of the limbic system.

A

Works with the ACC in evaluating emotional contexts – role in empathy
(encodes emotional awareness)

  • Connected to the ACC
  • Anterior portion considered to work with the ACC
  • Input -> Visceral information including pain
  • Classified as limbic sensory cortex
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21
Q

What might lesions in the insula result in ?

A

• Patients with lesions have defects in awareness of other peoples pain (empathy)

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22
Q

What is the function of the hypothalamus within the limbic cortex ?

A

Provide context

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23
Q

Draw the full limbic cortex network, including all the main structures involved and their role.

A

Refer to slide 2 on page 6.

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24
Q

Describe the underlying cause behind PTSD.

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
25
Q

Identify the main functions of the cingulate gyrus.

A

CINGULATE GYRUS

  • Emotion response regulation coordinated via connections with the 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)
26
Q

What are the main functions of effectors and regulators of the limbic system ?

A

1) Mediate emotional reactions (behavior and physiology) via ANS
2) Modulating learning/settings of Limbic system resetting according to conditions/memory

27
Q

Identify the main effectors and regulators of the limbic system.

A
  • Hypothalamus (major effector of limbic system + regulator)
  • Locus coeruleus (effector + regulator)
  • Periaqueductal grey (effector + coordinator of flight/flight/freeze responses)
  • Dorsal raphe nucleus (effector and regulator)
28
Q

Identify the main inputs, and outputs of the hypothalamus as a limbic system effector and regulator.

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
29
Q

Give examples of possible effects of the hypothalamus as an effector of the limbic system.

A

Autonomic: Cardiovascular, respiratory, piloerection Sweating etc

Endocrine: Stress response. PVN->CRH->ACTH ->cortisol

Behavioural: General level of activity up to and including ‘rage’ for pursuit of food, water, sex etc; Ingestion/disinterest in/of food; Fear behaviour; Increased sexual drive

Basic homeostasis: Fluid electrolyte; Feeding energy;
Thermoregulation; Reproduction; Sleep wake

30
Q

Describe functioning of the Locus Coeruleus as a limbic system effector and regulator.

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 LC maintains arousal and also effect autonomic nervous system output
• Projections FROM PAG selects fight or flight mode

31
Q

Describe functioning of the Periaqueductal grey (PAG) as a limbic system effector and coordinator of fight/flight/freeze responses.

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

-PAG has multiple modes/pathways:
1) Defensive fear network
• Amygdala -> vl PAG -> vagal paths (parasympathetic in freezing)
• Amygdala/CG -> dl PAG -> LC and BS (fight-or-flight switching)

2) Pain network
Pain regulation ->encephalin -> raphe nuclei -> 5HT dorsal horn -> interneurone block pain paths

32
Q

Give an example of how the threat response depends on context.

A
  • At distance cingulate gyrus (CG) processes response through lateral amygdala/striatum (PAG independent)
  • Close by central amygdala (CA) drives periaqueductal grey and other brainstem to panic mode (AS)
33
Q

Describe functioning of the Dorsal Raphe Nucleus (DRN) as a limbic system effector and regulator.

A
  • Midbrain nucleus projects an ascending system
  • Projects to 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
34
Q

Describe the theory of 5HT and depression/mood.

A

High 5HT level (from DRN)= Mania

Low 5HT level (from DRN)= Depression

35
Q

Describe the effect fo variant polymorphism in 5HT transporter gene (5HTT).

A
  • Blocked recharging of synaptic vesicles with 5HT
  • Diminishes transcription efficiency and expression
  • May increase risk of depression (under investigation)
  • Reduced communication between ACC and amygdala
  • Reduced size of amygdala and increased reactivity of amygdala to emotional stimuli
36
Q

Describe the findings in the limbic system of established depression.

A
  • Reduced metabolism in ACC
  • Reduced size of ACC
  • Reduced size of amygdala but inverse correlation with treatment (reduced amygdala volume recovered after antidepressants (plasticity – more neurons/ projections/ synapses))
  • Highest density of 5HTT in the ACC
37
Q

How does Paroxetine work ?

A

5HTT inhibitor

38
Q

Why is the hippocampus often considered not to be a limbic system structure ?

A

Has only indirect influence on emotion

39
Q

What is the main function of the hippocampus ?

A

Combines spatio-temporal information with emotional, sensory and cognitive information to establish new episodic memory (including memories for locations and events that take place at those locations)

40
Q

Describe anatomical location, and appearance of the hippocampus.

A
  • Deep in the temporal lobes
  • Elongated structure in the floor of the lateral ventricle
  • Name reflects its similarity to a seahorse
  • Rolled appearance
  • Evolutionarily old cortex
41
Q

Define hippocampal formation.

A

Hippocampus + association cortex

42
Q

Identify the main components and structure of the hippocampus.

A
  • Subiculum most inferior portion of the hippocampus
  • Subiculum connected to the Entorhinal areas, amygdala and nucleus acumbens
  • Dentate gyrus characteristic circuitry + 4 CA regions in cornua ammonis
43
Q

How does the hippocampus communicate with the cortex ?

A

Entorhinal area (rostral) is the main gateway for communication with the neocortex

44
Q

Identify the main types of memory.

A

Declarative memory, two types:

  • Episodic (recollection about a specific event in one’s past, tied to a specific time and place)
  • Semantic (general knowledge about the world)
45
Q

Describe the effects of hippocampal damage on memory.

A
  • EARLY hippocampal damage difficult to remember events of their daily lives, but seem to have an intact semantic memory, being able to learn school subjects such as languages and acquiring factual knowledge
  • Patients with hippocampal damage can retain memories of events that occurred years before to the onset of their brain damage.
  • Sparing of remote memory - undergoes consolidation gradient, memories gradually become independent of hippocampus as they are consolidated in other brain regions (neocortex).
  • Hippocampal amnesic patients displayed a deficit in their ability to imagine new experiences. This inability to construct from its individual components a mental narrative may reflect the synthetic defect (episodic memory amnesia).
46
Q

Draw a typical basic circuit for learning in the hippocampus.

A

Typical basic TRISYNAPTIC circuit in the hippocampus

Refer to slide 2 in page 11

  • Trisynaptic circuit, temporary consolidation in CA3 and more permanent in CA1.
  • “Place cells becomes active when an animal enters a particular place in its environment”
  • Other cells respond to other modalities such as odours, tactile info and timing giving an overall picture of context.
47
Q

Identify the main inputs into hippocampus.

A

3 inputs into hippocampus through related cortex for memory processing:

1) PLACE- Dorsal information stream processes spatial context and culminates in parahippocampal cortex

Caudal hippocampus processes extroceptive signals for scene learning

2) THINGS- Ventral information stream processes object recognition and culminates in perirhinal cortex

3) EMOTIONAL INFO- Rostral hippocampus processes interoceptive signals for emotional and motivational modulation

48
Q

Which of the following would be most activated by making the memory of a face ?

  • HPC
  • Endorhinal cortex
  • Parahippocampal cortex
  • Perirhinal cortex
A

HPC

49
Q

Which of the following would be most activated by making the memory of an object ?

  • HPC
  • Endorhinal cortex
  • Parahippocampal cortex
  • Perirhinal cortex
A

-Peririhinal cortex

+ Endorhinal cortex

50
Q

Which of the following would be most activated by making the memory of a place ?

  • HPC
  • Endorhinal cortex
  • Parahippocampal cortex
  • Perirhinal cortex
A

Parahippocampal cortex

51
Q

Describe Para hippocampal cortex function.

A

Role in:

  • Episodic memory (both spatial and non-spatial)
  • Navigation (both spatial and non-spatial)
  • Contextual and Scene processing (both spatial and non-spatial)
52
Q

Identify diseases which may affect the hippocampus.

A
  • Sensitive to stress (glucocorticoids)
  • Cushings disease and glucocorticoid administration -Ischemia sensitive
  • Atrophy of the hippocampus
  • Williams Syndrome
53
Q

Identify causes of atrophy of the hippocampus.

A
  • Alzheimers
  • Hypertension
  • Depression
  • Epilepsy
  • Cushings disease
  • Stress (PTSD)
  • Genetic disorders
  • Chronic alcohol use
54
Q

Define Williams Syndrome.

A

Genetic deletion syndrome in which there is developmental hippocampus effects.

  • Reduced blood flow to hippocampus
  • Different shape of hippocampus
  • Defective place learning
55
Q

Describe the effect of alcohol consumption on the hippocampus.

A

-Dose dependent negative correlation of
hippocampus size and non-dependent
moderate alcohol consumption over 30 years

  • Clinically, chronic alcohol intake detrimental effects on hippocampus related learning and causes damage there
  • Wernicke-Korsakoff syndrome – thiamine deficient alcohol related hippocampal damage and decrease in hippocampal learning
56
Q

What is the fornix ?

A

A major output tract of the hippocampus involved in memory

57
Q

Identify functions of the fornix.

A

-L-R segregation of output + segregation of output according to hippocampus processing, rostral/caudal

58
Q

Identify a possible disease affecting the fornix, and its clinical effects.

A
  • Glioma in wall of the lateral ventricle displacing both fornices
  • Memory deficits delayed recall for verbal and visuospatial info
59
Q

Identify the main functions of the PAG.

A
  • Coordinates emotional responses
  • Generates primary emotions (stimulation -> sham rage)
  • Independent of cognition and emotional perception