13. The limbic system Flashcards
What is the limbic system?
A region of the cortex - a group of cortical and subcortical nuclei found on the medial aspect of the frontal, parietal and temporal lobes
What is the function of the limbic system?
Part of the brain which controls motivation, emotion and memory (learning)
Involved in pleasure, pain, motivation and memory
Is responsible for rewarding animals when they increase their chance of survival e.g. eating/sex or for punishing them when they decrease their change of survival e.g. injury causing pain
Which other major system in the brain is the limbic system greatly connected to?
Is connected to the olfactory system
Allows animals to experience good memories when they smell nutritious food etc
In humans, why some foods can make you hungry and others make you nauseous - other smells can trigger memories or make you feel sexy
Which anatomical regions of the brain is the limbic system composed of and where are these structures located?
Composed of the cingulate cortex (anterior and posterior regions), the orbito-frontal cortex and the parahippocampal cortex
The cingulate cortex is located superiorly to the corpus callosum - curves all the way around
The orbito-frontal cortex is inferior to the corpus callosum and anterior
SO the posterior cingulate continues on into the anterior cingulate which continues on into the orbito-frontal cortex
The parahippocampal cortex lies in the medial temporal lobe
What is the blood supply to the limbic system?
Blood supply is from the anterior cerebral artery (anterior region) and the posterior cerebral artery (posterior most region)
An infarct in either of these arteries can affect the limbic system
What are the divisions of the anterior cingulate cortex?
Rostral anterior cingulate (near the head, more anteriorly positioned)
Caudal anterior cingulate (near the tail)
What are the functions of the different parts of the anterior cingulate cortex?
Rostral anterior cingulate - less known but thought to be the region which is involved with which actions to take to deal with the pain
Caudal anterior cingulate - where we register the quality of the pain i.e. how bad it is on a scale of 1 to 10
What is cingulotomy and what is it thought to be useful for?
This is the procedure of cutting into the cingulate gyrus to disrupt the passing of the rostrocaudal fibres
This is thought to reduce the emotional distress of pain i.e. reduce the emotional impact of the pain
What is the function of the posterior cingulate cortex?
We do not really understand it’s function properly BUT believed to be involved in visuo-spatial memory i.e. finding your way around a new city, being able to read a map
What is the parahippocampal gyrus and where is it located?
This is a key part of the cortex involved with learning and memory
Lies medially and inferiorly in the temporal lobe - closely connected to the subcortical structures within the temporal lobe - surrounds the hippocampus
In which lobes are the following horns of the lateral ventricle:
Anterior horn
Posterior horn
Inferior horn
Anterior horn - frontal lobe
Posterior horn - occipital lobe
Inferior horn - temporal lobe
What is meant by ‘subcortical’?
Lying below the cortex
What are the subcortical parts of the limbic system?
Hippocampus
Amygdala
Accumbens nucleus
Septal nuclei
These lie around the walls of the inferior horn of the lateral ventricles in the temporal lobe
Where is the hippocampus located?
Hippocampus lies along the medial wall of the inferior horn of the lateral ventricle
What is the fornix and what is it’s path in the brain?
Fornix - collection of the axons leaving the hippocampus moving underneath the corpus callosum towards the hypothalamus
Ends in the mammillary body of the fornix
What is the significance of neuronal connections between the hippocampus and the limbic system?
Give the pathway
Neuronal connections travel in a loop
Information from the cingulate cortex to the parahippocampal gyrus
Then to the hippocampus, along the fornix and to the mammillary body
Then to the anterior thalamus from which it goes back to the cingulate cortex
What is the function of the hippocampus?
Believed to register the time of day that a memory occurs and the spatial awareness of where that memory occurred - labels new experiences according to the place and time that they occurred
AND the commitment of new experiences into longterm memory
What can damage to the hippocampus result in and what is this known as?
Damage to the hippocampus results in a failure to transfer new experiences into long term memories
This is known as anterograde amnesia
What is Wernicke-Korsakoff syndrome?
This is a form of encephalopathy commonly observed in alcoholics who have a deficiency of B1 (thiamine) in the brain
(Is a form of anterograde amnesia)
What is encephalopathy?
A disease in which the functioning of the brain is affected by some agent or condition
What are the symptoms of Wernicke-Korsakoff syndrome?
Some level of anterograde amnesia
Some degree of retrograde amnesia
Confabulation (can’t remember what happened at a certain time so you make something up to fill the gap and then you believe that this is what occurred)
Apathy
What is the cause of Wernicke-Korsakoff syndrome?
Due to damage to the hippocampal circuit, in particular the mammillary bodies and their projection to the anterior thalamus
What is temporal lobe epilepsy (TEL)?
When damage or compression to the temporal lobe occurs e.g. during a difficult birth - specifically damage to the hippocampus and amygdala
Produces disorders of memory and emotion
What are the symptoms of temporal lobe epilepsy?
Often experience deja vu
Patients experience verty strong surges of dread or joy for no apparent reason
Also experience hallucinations - feel as thought they are living in a dream
What is Kluver-Bucy syndrome and what is it’s cause?
Damage to (or bilateral removal of) the amygdala at the tip of the temporal lobes and the adjacent temporal cortex
The patients lose all sense of fear
Where is the amygdala located?
What does electrical stimulation of the amygdala result in?
Embedded in the entorhinal (olfactory) cortex in anterior medial temporal lobe
Electrical stimulation produces pain, fear and terror responses
What is the amygdala composed of?
The amygdala is not a uniform body but it is formed of many subnuclei (like the thalamus)
What is the function of the amygdala?
Results in the sensation of fear and anxiety
Stimulates the fight or flight response of the sym NS (sends commands to the hypothalamus which communicates with the symp NS)
How can damage to the amydala present in patients?
Unable to judge when a face shows a fearful expression
Misinterpretation of fearful events - leads to excessive risk taking, odd relations and financial decisions
Essentially decreases one’s ability to recognise emotion in others and thus makes it harder to empathise with them and conduct normal social relationships
Is the accumbens nucleus part of the limbic system
Anatomically part of the basal ganglia
Functionally and physiologically part of the limbic system
What is the function of the accumbens nucleus?
Receives dopaminergic fibres as part of the mesolimbic dopamine pathway
Involved in the initiation and termination of behaviours i.e. motor actions that trigger reward pathways e.g. eating
Where do the septal nuclei lie?
These lie at the base of the septum pallucidum - merge into the basal nucleus of Meynert
Where does the fornix end?
Reaches down almost vertically to end in the anterior hypothalamus - the mammillary body - where there are the septal nuclei
What is Papez’s circuit?
This is the idea that the connections of the limbic system form a closed loop
Postulated that this closed loop is somehow necessary for the formation of memories
What is the function of the orbitofrontal cortex?
How to behave to an anticipated threat i.e. how to avoid pain/injury
An overactive orbitofrontal cortex has been observed in which neurological condition?
OCD
