The limbic system, emotion, the hypothalamus, appetites Flashcards
Identify the core components of the limbic system, and their effectors.
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
State the main function of the limbic system.
LIMBIC SYSTEM evaluate brain activity, memories, environmental cues and state of the individual and acts on this information to maximise survival strategies
Is the parahippocampal gyrus a core component of the limbic system ? Why or why not ?
Parahippocampal gyrus not a core component of Limbic system because it feeds information in - indirect role
Where is the amydala located ?
- Anterior temporal lobe at the tail of caudate nucleus and rostral to hippocampus
- Grey matter blob with central, corticomedial and basolateral nuclei
Define Klüver-Bucy syndrome, and identify clinical features of it.
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
Identify possible causes, and treatment of Klüver-Bucy syndrome.
Causes (examples): • Herpes encephalitis • Trauma • Tumours • Hypoxia • Pick’s disease
Treatment is symptomatic and may include the use of psychotropic medications.
Identify pathologies affecting the amygdala.
Klüver-Bucy syndrome (anterior temporal lobe lesion)
Urbach-Wiethe disease (more specific damage to amygdala)
Explain the underlying cause of Urbach-Wiethe disease, and identify it’s main clinical features.
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.
What does electrical stimulation of the amygdala result in ?
• Electrical simulation leads to anxiety and fear
Which parts of the amydala are activated in fear, and anxiety respectively ?
• 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
Identify functions of the amygdala.
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)
Identify the main inputs into the amygdala. Where do these inputs go ?
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
Where in the amygdala do outputs leave from ?
OUTPUTS from the CENTRAL NUCLEUS
Explain how the amygdala can learn a modified fear response.
- 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).
Describe the pathways utilised for emotional responses to food in the amygdala.
Input to corticomedial nuclei from olfactory bulb (taste info)
Output from corticomedial nuclei to the hypothalamus to drive a response
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.
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
What is the function of the anterior cingulate as part of the limbic cortex ? of the motor cingulate ?
- 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
Describe the effector pathways of the limbic cortex in emotion.
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.
Which part of the cingulate cortex is considered to be primary limbic cortex ? What does this mean ?
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
Describe the role of the insula as part of the limbic system.
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
What might lesions in the insula result in ?
• Patients with lesions have defects in awareness of other peoples pain (empathy)
What is the function of the hypothalamus within the limbic cortex ?
Provide context
Draw the full limbic cortex network, including all the main structures involved and their role.
Refer to slide 2 on page 6.
