limbic system Flashcards
What are the core components of the limbic system?•
- Amygdala
- Hipocampus
- Limbic cortex
Where is the amygdala?
- Anterior temporal lobe
- Tail of the caudate nucleus
- Rostral to the hippocampus
What are the nuclei of the amygdala?
- Central
- Corticomedial
- Basolateral (basal and lateral)
Kluver Bucy
• Associated with damage to the anterior temporal lobes • Common symptoms: - Hyperorality - Placidity - hyper sexuality - visual agnosia - memory loss - hyper metamorphosis - enhanced aggression and anger - seizures - anger - dementia
What are the causes of kluver bucy syndrome?
- herpes encephalitis
- Trauma
- Tumours
- hypoxia
- Pick’s disease
What happens when there is damage to the amygdala specifically?
Abrogates fear
Urbach Wiethe disease
- Calcificaiton in the temporal lobes
- Without fear
- Defecrs in judgment of emotion present in facial expression
- Poor performance in odour-figure association test
- Defects in remembering positive and negative emotional content of pictures
What happens when the amygdala is electrically stimulated?
• Anxiety and fear
What nucleus is activated by fear?
Central (and the bed of the stria terminalis BST)
What are the outputs of the amygdala?
• Central nucleus • Output to hypothalamus via the stria terminalis • Output to brainstem structures: - Locus ceruleus - parasympathetics - ventral tegmental area - periaqueductal grey matter
What are the inputs to the amygdala?
- Can be extant objects, imagined or contextual
- Can be from inside or outside of the CNS
- Inputs go to the lateral nucleus
- Fast track via the thalamus
- Longer route via the cerebral cortex (+ hippocampus_)
Which part of the amygdala is responsible for comparing the incoming sensory stimuli to previous stimuli?
The basolateral amygdala
What makes up the limbic cortex?
Anterior and anterior portion of the middle cingulate gyrus
What is the role of the anterior cingulate gyrus?
- Encodes basic emotion: happiness, sadness, fear
- Encodes emotional memory
- has a top down influence and works to recode the amygdala
Describe the top down influence of the amygdala
- Computes relevance/outcomes and drives appropriate behaviour
- Provides conflict resolution
- Part of the pain network
What are the effector pathways of the anterior cingulate gyrus?
- Motor reactions
- Specific zone for driving face muscles
- Direct outputs to the autonomic NS and indirect via the amygdala
What is the role of the insula?
- Works with the ACC to evaluate emotional contexts
- Role in empathy
- Encodes emotional awareness
PTSD
- Hyporesponsive and decreased volume ACC
- Amygdala becomes hyperresponsive to. trauma related stimuli
- Top down control of the amygdala is therefore missing in PTSD
What are the effectors of the limbic system?
- Hypothalamus
- Locus coeruleus
- Periaqueductal grey
- Dorsal raphe nucleus
What are the inputs to the hypothalamus
- Limbic cortex
- Amygdala
- Olfactory systems
- Viscera
- Pain
- Internal signals
What are the outputs of the hypothalamus?
- Neuronal to the brainstem and spinal cord
* Hormonal
What is the locus coeruleus?
Midbrain nucleus involved in physiological responses to panic and stress
What are the inputs to the locus coeruleus?
- Cingulate gyrus
- Amygdala
- PAG
- Hypothalamus
What is the function of the locus coeruleus
- Promotes alertness and wakefulness
- Promotes anxiety and the formation and retrieval of emotional memories
- Projections to the hypothalamus maintains arousal and effects autonomic nervous system output
- Projections from the APG select fight or flight mode
What is the dorsal raphe nucleus?
- Midbrain nucleus that projects on ascending system
- Projects to and receives from the amygdala and aCC
- Serotonin
What is the function of the dorsal raphe nucleus?
- Determines tonic limbic activity and dynamic mood state
* Processes descending pain paths from he periaqueductal grey to the dorsal raphe nucleus to the spinal cord
Depression
- Reduced metabolism in the ACC
- Reduced size of the ACC
- Amygdala is reduced in size and hyperactive
- Highest density of 5HTT in the ACC
Function of the hippocampus
- Indirect influence on emotion
* Important in forming episodic memories
Where is the hippocampus?
- Deep in the temporal lobe
- Floor of the lateral ventricle
- Rolled appearance
What is the hippocampal formation?
Hippocampus and associated cortex
What is the parahippocampal gyrus
Perirhinal cortex, entorhinal cortex and parahippocampal cortex
Entorhinal area
Main gateway for communication with the neocortex
Subiculum
Most inferior part of the hippocampus, connected to the entorhinal areas, amygdala and nucleus accumbent
What is declarative memory?
Episodic and semantic memory
What is episodic memory?
Recollection of events in a person’s past
What is semantic memory?
General knowledge about the world
Early damage of the hippocampus
- Difficult to remember events of daily lives
* Intact semantic memory- can gain factual knowledge
Adults with hippocampal damage
- Can retain memories of events that occurred years before the onset of the damage
- difficult to remember events of daily life
