TASK 5 - LIMBIC SYSTEM Flashcards Preview

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Flashcards in TASK 5 - LIMBIC SYSTEM Deck (32):
1

emotions

= automatic, largely unconscious behavioural + cognitive responses triggered when the brain detects a positively/negatively charged significant stimulus
- when detected it sends commands to networks controlling the expression of emotional states
- regulatory mechanisms mostly mediated by subcortical structures: amygdala, striatum, hypothalamus, brain stem

2

feelings

= conscious perceptions of emotional states

3

historical theories of limbic system
- Broca

limbic system = cingulate gyrus + hippocampus (+ amygdala)

4

historical theories of limbic system
- James: peripheral feedback theory

1. emotional stimuli
2. processed in sensory systems
3. transmitted to motor cortex --> produce emotional responses in the body
4. feedback signals to cortex convey sensory info about body responses
- feeling = cortical processing of sensory feedback; comes when bodily expression of emotional response enters consciousness

5

historical theories of limbic system
- Cannon-Bard: central theory

= emotions are explained by processes within the CNS
1. sensory info from thalamus
2. hypothalamus (mammillary bodies) + cerebral cortex
2a. descending connections to brain stem and spinal cord give rise to emotional responding
2b. ascending connections to cerebral cortex give rise to feelings
- feelings: thalamocortical pathways --> projections to cerebral cortex produce conscious feelings

6

sham rage (Bard experiment)

= cut out cerebral hemispheres of monkeys, only left hypothalamus
- if we take away cortex, no control over rage anymore
- sham rage in monkeys only when caudal/posterior hypothalamus lesioned
1) hypothalamus is critical centre for coordination of somatic + visceral motor components of emotional behaviour
2) subjective experience of emotion depends on cortex --> but expression of coordinated behaviours doesn’t
--> hypothalamus is responsible for the brain’s evaluation of the emotional significance of stimuli + reactions depend on this appraisal

7

historical theories of limbic system
- Papez circuit

limbic system = added 1) cingulate gyrus 2) hippocampus 3) mammilary bodies (hypothalamus) 4) anterior nucleus of thalamus
- cingulate cortex: receives hypothalamic output in creation of feelings
1. sensory info from thalamus
2. hypothalamus (mammillary bodies)
2a. descending connections to brain stem and spinal cord give rise to emotional responding
3. ascending connections: (anterior) thalamus
4. cingulate cortex (where signals from cortex & thalamus converge to produce feelings)
5. hippocampus
- feeling = convergence at cingulate cortex accounts

8

historical theories of limbic system
- McLean

limbic system = added PFC, amygdala, hypothalamus
- hippocampus = point of convergence

9

niewenhuys model

- light pink: Broca's limbic cortex + allocortex (uncus, medial parahippocampal gyrus, ictus, ventral cingulate gyrus, caudal orbitofrontal cortex)
- dark pink: hippocampus
- blue arrow: Papez circuit
- amygdala
- close connection between medial limbic system (amygdala + hippocampus and olfactory system

10

niewenhuys model
- high-end of limbic system

= interacts with voluntary behaviour system of cerebrum
- limbic lobe = intermediate level between neocortex and limbic system
- important roles influencing motivational states, feeling accompanying these states + emotional expression

11

niewenhuys model
- low-end of limbic system

= interacts with autonomous centres + generation of instinctive behaviours
- hypothalamus = top of autonomous motor system hierarchy
- central pattern controllers

12

niewenhuys model
- interface

limbic system = interface between (1) cerebral neocortex + (2) brains stem autonomous system
1) limbic arousal: accompanied by increases in motivation + strong negative/positive affect
- negative affect = central grey area (CGA)
- positive affect = VTA
- resistant to habituation
- input: dominated by visceral sensory structures (= limbic areas)
2) non-limbic arousal: evoked by stimulating ascending reticular activating system (ARAS) in brainstem
= arousal when we encounter a novel/unexpected stimulus
- orienting response to novelty
- habituation with repeated stimulation
- input of mixed sensory nature

13

niewenhuys model
- memory subsystem

= hippocampus; Papez circuit
1. hippocampus
2. fornix
3. mammilary bodies
4. anterior nucleus
5. via cingulate cortex back to hippocampus

14

niewenhuys model
- emotional subsystem

= amygdala
1. caudal-medial amygdala
2. via stria terminalis
3. anterior diencephalon, anterior commissure
4. septal nuclei + preoptic nucleus
- extended amygdala: central, medial nuclei + BST (bed nucleus of stria terminalis)

15

niewenhuys model
- default mode network

= both subsystems together
1) hippocampal-diencephalic circuit: episodic memory division + spatial memory/orientation division
- extend to cerebral cortex via parahippocampal gyrus, ictus to posterior cingulate cortex (PCC)
--> PCC: medial hub of default mode network
2) temporo-amygdala-orbitofrontal network: integration of visceral and emotional states with cognition and behaviour
- centred on amygdala, connected through uncinate fascilus --> via orbitoinsular cortex to anterior cingulate cortex
--> ACC: medial hub of default mode network

16

systems of emotional behaviour integration
1. volitional movement

= classical motor areas of voluntary somatic motor control
- cortex --> brainstem
1) forced smile = voluntary contraction of facial muscles
- pyramidal smile: driven by motor cortex --> communicates with brainstem + spinal cord via pyramidal tract

17

systems of emotional behaviour integration
2. emotional expression

= descending projections from medial + ventral forebrain --> terminate on visceral motor centres in reticular formation + somatic motor neurone pools (also receive info from volitional centres)
2) spontaneous emotional smile (“duchenne smile”)
- motivated by motor areas in anterior cingulate gyrus
- access facial muscles via multi-synaptic extrapyramidal pathways through reticular formation

18

systems of emotional behaviour integration
- disruption

1) disruption in fake smile = not able to voluntarily smile, but spontaneous (evoked) smile possible
2) disruption in real smile = not able to smile due to emotions, but when asked to can produce voluntary smile

19

amygdala

- basolateral nuclei = main input
- central nuclei = main output
- projects to autonomic and endocrine system

20

physiological stress-response
1. autonomic response

= autonomic nervous system: sympathetic nervous system (= prepare for action)
- fast response

21

autonomic response

1. central nuclei of amygdala
2. lateral hypothalamus
3. adrenals (medulla)
4. release adrenaline (epinephrine)

22

effects of adrenaline

- mobilisation of energy
- ready for action
- suppression of gestation

23

physiological stress-response
2. endocrine response

= endocrine system: HPA axis (= hypothalamus-pituitary-adrenal cortex)
- slow response --> release of hormones

24

endocrine response

1. central nucleus of amygdala
2. paraventricular nucleus of hypothalamus --> releases CRF/AVP
3. pituitary --> releases ACTH
4. adrenals (cortex)
5. release cortisol

25

effects of cortisol

- suppression of HPA axis (homeostasis, negative feedback)
- mobilisation of energy
- suppression of immune system
- behavioural inhibition/ attention
- motivation
- memory
- effect on cognition --> dorsal hippocampus --> decreases HPA axis even more

26

fear response

= avoidance of actual dangerous situation
1. central nuclei of amygdala
2. medial hypothalamus
3. periaqueductal gray (PAG)

27

anxiety response

= approaching potentially dangerous situation
1. medial PFC
2. cingulate gyrus
3. ventral hippocampus
4. basolateral amygdala
--> McLean limbic system (Papez)

28

behavioural stress-response

- coping = try to influence + control environmental stressors
- need learning + memory: respond better based on prior experiences

29

fear conditioning

1. lateral nucleus = input; receiving info about CS from thalamus; site of synaptic change during fear conditioning
2. sensory input reaches directly + indirectly
3. amygdala + cortex activated simultaneously
- amygdala responds to danger before cortex can even process the info --> before we consciously feel fear
4. central nucleus = fear associations are formed + stored; transmitting info about CS and US from lateral nucleus
5. central nucleus sends outputs to hypothalamus about following physiological responses

30

role of amygdala in fear conditioning

- mediates emotional procedural memory
--> ventral part of dorsal division = mediate long-term memory of CS-US association
--> site of memory storage in fear conditioning
- mediates emotional component of declarative memory
--> dorsal part of dorsal division = initiate learning when CS and US are paired

31

anxiety disorder

= inappropriate activation of amygdala (via BST) --> HPA-axis hyperactive --> increased cortisol release --> degeneration of hippocampus --> no decreasing of cortisol --> vicious cycle

32

affective disorder

1. monoamine hypothesis: mood is tied to levels of released monoamine neurotransmitters in brain (NE, 5-HT)
- depression: consequence of deficit in one of these modulatory systems
- might promote long-term adaptive changes
2. diathesis-stress hypothesis: HPA-axis is main site where genetic + environmental influences converge to cause mood disorders
- diathesis: predisposition for a certain disease
- hyperactivity HPA: cause of depression
- hippocampus feedback disrupted --> due to genes, monoamines, early childhood experiences