what body responses are involved in the fight or flight response
- heart rate increases
- sweating
- resp. rate etc.
- defecation
- micturition
- fascial expression
- evacuation
- muscle blood blood to prepare to fight
what are the two main parts of the limbic cortex
cingulate gyrus
insula
what does the limbic system process
emotion and related brain activity, memories, environmental cues and state of the individual and acts on this information to maximise survival strategies
what does the amygdala focus on
emotion
what does the hippocampus focus on
memory
what are the two structures which allow output from this area of processing
hypothalamus and brainstem structures
where is the amygdala located
in the anterior temporal lobe at the tail of the caudate nucleus and rostral to the hippocampus
what are the four nuclei of the amygdala
central nucleus, corticomedial nuclei and the basal and lateral nuclei
what is Klüver-Bucy syndrome
associated with damage to the anterior temporal lobes
• Hyperorality
• Placidity (lack of fear)
can be caused by:
- herpes encephalitis
- trauma
- tumours
- hypoxia
- picks disease
if one experiences fear what nuclei in the amygdala is activated
the central nucleus and the bed nucleus of the stria terminalis (BST)
it is this area in which the centres are enhanced in anxiety disorders
where does input enter the amygdala
lateral nuclei
where does output exit the amygdala
the central nucleus
there are three types of fear pathway, all related to different aspects of the fear
- stimulus
- concept
- context
stimulus pathway
this takes a fast tracked pathway to the thalamus - doesn’t reach our actual consciousness (subliminal short route)
(view of a snake or hiss of a snake)
the concept pathway
this is via the cerebral cortex
this is the idea of a snake or a previous memory you may have
the context pathway
this is via the hippocampus and insinuates the snake is in the room with you
how can the amygdala learn - stimulus pairing
this is noise or scene associated with a fear stimulus can itself elicit fear
this extends to context as well such as a place or a person
the lateral nucleus responds to the stimulus pairing
then the central nucleus droves the response via two main centres:
- the hypothalamus (this is via the stria terminalis
- the brainstem
what is the stria terminalis
a c shaped structure that ends in the hypothalamus and the BST (basal nucleus of the stria terminalis)
if the central nucleus of the amygdala outputs via the brainstem, where does this take place
- periaqueductal grey matter (PAG)
- locus coeruleus (LC)
- parasympathetics (solitary nucleus, dorsal vagal nucleus)
- ventral tagmental area
what is valency
determining if something you are experiencing is good or bad
there are three areas of the cingulate gyrus, what are these known as?
- ACC
- MCC
- PCC
anterior/middle/posterior Cingulate gyrus
what makes up the limbic cortex - this processes emotion
the ACC and anterior portion of the MCC
also as a side note remember that the insulation is also considered to be part of the limbic cortex
ACC connects to where when thinking about effectors
the amygdala and to effectors in the brainstem
this encodes basic emotions such as happiness, sadness and fear, also focuses on emotional memory of fear
MCC connects to where when thinking about effectors
to the motor Cortex so primarily movement and behaviour
what is the top down influence of the anterior cingulate
- 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
ACC + some of the MCC are considered to be called what
the primary limbic cortex
thesis a higher level of processing emotion and is combined with the top down functions of the amygdala
deals with emotional conflict “friend tied to a chair”
determines motivators
what is the main role of the insula
empathy
this is closely connected to the ACC and works with it
it gets input from the visceral information including pain
limbic sensory cortex and it encodes for emotional awareness
what happens to the limbic system in PTSD
part of the ACC becomes hypo-responsive and there is a reduction in the size of the ACC
so ACC works less so is unable to perform top down conditioning
Amygdala becomes hyper-responsive to trauma and related stimuli
the top down control of the amygdala by the ACC is therefore missing in PTSD
locus coeruleus - effector and regulator
this is a midbrain nucleus that is involved in the physiological response to panic and stress
there are noradrenaline fibres that project from the nucleus to the widespread brains structures
promotes alertness and wakefulness
can also promote anxiety + formation and retrieval of emotional memories from the amygdala via dense projections
Periaqueductal grey (PAG) - fight/flight/freeze responses
inputs from the cingulate gyrus and the amygdala
projects to the nucleus of the solitary tract, dorsal nucleus of the vagus, intermediolateral column
projects from the PAG to LC selects the fight to flight response
what is the PAG freeze pathway
ventrolateral (vl) PAG -> vagal paths (parasympathetic in freezing)
what is the PAG fight or flight pathway
dorsolateral (dl) PAG -> LC and BStem (fight-or-flight switching)
why is traumatic pain often not felt till mins/hours after an incident
Pain regulation ->encephalin -> raphe nuclei -> 5HT dorsal horn -> interneuron block pain paths
Dorsal raphe nucleus (DRN)
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
In established depression what are the effects on the limbic system
- Reduced metabolism in ACC
- Reduced size of ACC
- Amygdala reduced size and hyperactive
HIPPOCAMPAL FORMATION and function of the hippocampus
Hippocampus AND associated cortex
- 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 Alzheimers disease, genetic syndromes and chronic alchohol use
fornix
major output role for memory from the hippocampus
Wernicke-Korsakoff syndrome
thiamine deficient alcohol related hippocampal damage and decrease in hippocampal learning
ATROPHY OF THE HIPPOCAMPUS FOUND IN
- Alzheimer’s disease
- Hypertension
- Depression
- Epilepsy
- Cushing’s disease
- Stress (PTSD)
- Genetic disorders
- Chronic alcohol use
