Limbic System Flashcards
What are the three primary parts of the limbic cortex?
- Orbitofrontal - including subcallosal area
- Cingulate gyrus - surrounding corpus callosum
- Medial temporal cortex - includes parahippocampal gyrus
What is the general function of the limbic cortex?
Exchanges information with vast areas of the neocortex to help integrate all sensory and motor information into a neural representation of “self”
Where is the hippocampus located?
Deep to parahippocampal gyrus, adjacent to inferior horn of lateral ventricle, posterior to amygdala
How many cellular layers does the cortex have and why?
3 cellular layers, as it is one of the oldest parts of the brain
What are the three nuclei of the hippocampus?
- Dentate gyrus
- Ammon’s Horn (CA1, CA3)
- Subiculum
What is the general function of the orbitofrontal cortex?
Seat of wisdom, controls your intrinsic motivations
What is the general function of the cingulate gyrus?
Control in emotions and sadness -> lesion = no sadness with pain
What is the parahippocampal gyrus also called? What is its function?
Entorhinal cortex. Its function is the “gateway to the hippocampus”, receives information from limbic association cortex and projects to the hippocampus
What nuclei project directly to the hippocampus for the purpose of fear and pleasure memory?
Amygdala - fear
Septal nuclei - pleasure
Contributes to motivational states
What is the purpose of the reticuular formation with respect to the hippocampus?
Project serotonin, dopamine, and norepinephrine to hippocampus for regulation of mood (emotional tone)
What is the first nucleus to process information in the hippocampus and what does it do?
Dentate gyrus, receives fibers from entorhinal cortex and projects to Ammon’s Horn and subiculum
How do Ammon’s Horn and Subiculum project out, and what neurotransmitter type do they use?
They project out through the C-shaped fornix, with the first part being called the fimbriae.
Entire circuit is excitatory, reinforces memory formation
Why is the hippocampus prone to ischemia or seizure?
Entire circuit is excitatory with high energy demands in a small space
Where do Ammon’s horn neurons primarily project to?
- Septal area - for pleasure center, limbic system
2. Back to orbitofrontal cortex - limbic system
Where do subiculum neurons primary project to?
Mamillary bodies
What is the Papez circuit and what is its function?
Hippocampal efferent (subiculum) -> mamillary bodies -> mtt -> anterior nucleus of thalamus -> cingulate cortex -> entorhinal cortex.
Plays a role in emotions / declarative memory
What are two hippocampal efferents which do not travel in the fornix?
Amygdala, entorhinal cortex (since these are directly adjacent)
What happened to patient HM?
Anterograde amnesia due to bilateral medial temporal lobectomy for treatment of seizures, destroying his hippocampus
What is the other name for Korsakoff’s psychosis and what is its etiology?
Amnestic confabulatory syndrome
B1 deficiency leading to degradation of medial diencephalon, including medial thalamus + mamillary bodies.
Patients are intelligent but have anterograde amnesia, and make up answers to compensate for their memory loss.
Where is the amygdala and what surrounds it? What is it derived from?
Almond-shaped nucleus derived from telencephalon. It is anterior to the hippocampus in medial temporal lobe, and surrounded by the piriform cortex. Can be seen under the uncus and is the physical cause of the bulge.
What are the four main afferents to the amygdala?
- Olfactory - for feeding and reproduction
- Autonomic - from caudal solitary nucleus
- Visual - integrated from limbic cortex - important in higher animals
- Mood - from reticular formation
What nucleus processes olfactory information in the amygdala?
Corticomedial
What nucleus processes visceral and autonomic information in the amygdala?
Central
What nucleus processes cognitive information in the amygdala, and is the most important in humans?
Basolateral nucleus -> mostly visual information
Good because dorsolateral prefrontal cortex is also important in cognitive functions “seat of reasoning”
What are the amygdala’s efferents and their function?
- Hypothalamus - feeding, thirst, reproductive, endocrine
- Brainstem - for PANS and SANS
- Hippocampus - allow emotions to influence memory
- DM thalamus + limbic association cortex - integrate cognitive + sensory info about environment
What does the amygdala have reciprocal connection with?
DM thalamus and limbic association cortex - for integration of senses + emotions + personality
What is the general function of the amygdala?
Aversion center which analyzes the environment for cues which signify danger.
Has a strong function in inducing learning and memory especially when a situation evokes a strong emotional response -> survival
What happens when you stimulate the amygdala?
Increased attention, related to induction of fear + defense mechanisms, + SANS response.
What is the name of the disease where the amygdala degenerates bilaterally and you lose ability to see fear on peoples’ faces
Urbach-Wiethe disease
What does neurotransmitter imbalance of the amygdala underlie?
Anxiety and panic disorders
What is Kluver-Bucy syndrome? What are its characteristic features?
symptoms which accompany bilateral damage of amygdala, seen mostly in monkeys.
Marked by hyperorality, placidity (failure to show fear or anger), hypersexuality, and hyperphagia
What is the substantia innominata? Where is it located?
Unnamed substance - basal forebrain, located between orbitofrontal cortex and hypothalamus
What is the basal forebrain region called in gross view and why?
Anterior perforated substance, due to the blood vessels which enter the ventral telencephalon just rostral to the optic chiasm
What three main nuclei make up the basal forebrain? Where are they?
- Nucleus accumbens - ventromedial extension of caudate
- Septal nuclei - hangs ventral from septum pellucidum
- Nucleus basalis of Meynert - ventral to anterior commissure
What five things project to the basal forebrain?
Hippocampus, amygdala, limbic cortex, reticular formation, olfactory (medial stria) to septal nuclei
What is the only afferent connection to the hypothalamus through the fornix?
Septal nucleus projects to it through the fornix
What is the function of nucleus basalis and through what does it project?
Releases acetylcholine to the neocortex via the external capsule (lateral to basal ganglia)
This functions to strengthen memory formation
Where does nucleus accumbens project? What is its function?
Hypothalamus and ventral regions of globus pallidus
Functions in regulation of motor patterns associated with addictive behaviors, i.e. smoking, gambling, video games, drugs
What is the function of the basal forebrain as a whole?
Gratification center, rats will stimulate themselves for a pleasurable feeling
In what way are the septal nuclei similar to nucleus basalis?
Sends cholinergic axons to strengthen memory in relationship to pleasurable experiences, except it projects to hippocampus instead of neocortex (nucleus basalis).
