The Limbic System, emotion, the hypothalamus and appetites Flashcards
(40 cards)
1
Q
What are the main types of sensory inputs that can be put into the cortex?
A
- visual
- auditory
- feel
- memory
- context
2
Q
What are the core components of the limbic system
A
- Amygdala – emotion
- Hippocampus (+ cortex) [H. formation] = memory
- Limbic cortex – cingulate gyrus/insula
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
4
Q
What are the effectors of the limbic system?
A
- Hypothalamus
- Brainstem structures
**drive responses
5
Q
Describe the amygdala
A
- Grey matter blob with central, cortico-medial and basolateral nuclei
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)
7
Q
What is thought to cause Klüver-Bucy Syndrome?
A
- Herpes encephalitis
- Trauma
- Tumours
- Hypoxia
- Pick’s disease
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)
9
Q
In what disorders are the centres of the amygdala enhanced?
A
anxiety disorders
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
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)
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
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)
14
Q
What is responsible for higher order functions in evaluating the survival value of an emotional response?
A
Cingulate Gyrus
15
Q
What components form the limbic cortex?
A
Anterior (ACC) and Anterior Portion of the Middle (MCC) involved in emotions
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)
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
Describe the function of the hypothalamus as an effector and regulator of the limbic system
* 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
What is the role of the locus coeruleus in the limbic system?
* 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
Describe the role of the periaqueductal grey (PAG) in the limbic system
* 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
What are the modes/pathways of the PAG?
* 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
Illustrate how threat response depends on context
* 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
What is the function of the dorsal raphe nucleus in the limbic system
· 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
Describe the 5HT processing and predisposition to depression in normal individuals
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
How is the 5HT processing changed in depression?
* 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
What is the impact of the hippocampus on emotion?
indirect influence only
34
How does the hippocampus work?
* Combines spatio-temporal information with emotional, sensory and cognitive information --\> to establish new episodic memory
35
What are the functions of the hippocampus?
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
What are the 3 major inputs into the hippocampus?
* Emotional information
* Things
* Places
\*\*Object and face recognition, conceptual identiy and salience
37
In what conditions is atrophy of the hippocampus found?
* Alzheimer’s Disease
* Hypertension
* Depression
* Epilepsy
* Cushing’s Disease
* Stress (PTSD)
* Genetic Disorders
* Chronic alcohol use
38
What is the fornix?
* A major output tract of the hippocampus involved in memory
39
What does the fornix project to?
* 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
Summarise the function of the hippocampus and associated cortex (hippocampal formation)
* 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
