24.3 Components and Connections of the Limbic System Flashcards
Which systems provide input to the limbic system?
- Sensory
- Reward
- Decision making
What does the parahippocampal gyrus have?
Reciprocal connections with most associated cortex
What is the Papez circuit?
The circuit found within the limbic system.
Draw and describe the Papez circuit.
[IMPORTANT]
The circuit goes in this order:
- Cingulate gyrus (1)
- Parahippocampal gyrus (via the cingulum)
- Denate gyrus + Hippocampus (2) (via the perforant path)
- Fornix/fibria
- Mammillary bodies (3)
- Mammillothalamic tract
- Anterior nucleus of dorsal thalamus
And then back to the cingulate gyrus.
What is the amygdala and where is it found?
- It is a collection of nuclei in the medial part of the anterior pole of the temporal lobe.
- It is part of the limbic system and it one of the most important parts of the brain for emotion.
Describe the structure and function of the different parts of the amygdala.
There are 3 main groups of nuclei:
- Basolateral (green) -> Receives input from the auditory, somatosensory and nociceptive systems. Responsible for emotional response and emotional (reward) memory.
- Centromedial -> Outputs to produce visceral responses (e.g. heart rate increases)
- Cortical -> Part of the olfactory cortex
Summarise in detail the functions of the amygdala.
- Processing social indicators of emotion -> Especially facial expressions and vocal expressions of fear
- Emotional conditioning -> Learning to associate certain stimuli with fear
- Consolidation of emotional memories -> Memories with stronger emotions (e.g. someone crying) are remembered more strongly
- Inducing the actual feeling of fear?
- Olfactory processing
What is the basic circuit of Papez, starting from the hippocampus?
Hippocampus –> mammillary bodies –> anterior thalamic nucleus –> cingulate gyrus –> entorhinal cortex –> hippocampus
(He-Man Ate Cat)
Which structure links the hippocampus to the mammillary bodies?
Fornix
Which structure links the mammillary body to the anterior thalamic nucleus?
Mammillothalamic tract
What is an additional structure that is between the cingulum and entorhinal cortex in the Papez circuit?
Parahippocampal gyrus
Where do the anterior thalamic nuclei project to?
Neocortex
What does the parahippocampal gyrus have reciprocal connections with?
Association cortices
What are the three main groups of nuclei that make up the amygdala?
- Centromedial
- Cortical
- Basolateral
Where is the amygdala?
Medial part of anterior pole of temporal lobe
Adjacent to olfactory cortex
What is the function and output of the centromedial nucleus of the amygdala?
- Visceral responses: ANS, endocrine system, simple motor responses
- Output to VMH, neurosecretory hypothalamus
What is the function and output of the cortical nucleus of the amygdala?
- Receives olfactory info
- Pheromones –> elicit social and sexual behaviour
What is the function and output of the basolateral nucleus of the amygdala?
- Emotional response; input from higher order sensory regions
- Outputs to centromedial nucleus and basal ganglia for planning/action, or thalamus for relay
What are the functions of the inputs tobasolateral and central nuclei of the amygdala?
- All sensory association cortices
- Direct sensory input from thalamus
- Cortical amygdala
- Entorhinal cortex/hippocampus
- Cingulate gyrus, prefrontal, septal areas
- Brainstem
- All sensory association cortices: auditory, somatosensory, nociceptive systems
- Direct sensory input from thalamus
- Cortical amygdala: olfactory
- Entorhinal cortex/hippocampus: memory
- Cingulate gyrus, prefrontal, septal areas: emotions, reward processing, top-down control, reinforcement
- Brainstem: visceral sensory
What are the efferent pathways from the amygdala?
- Amygdalofugal tract
- Stria terminalis
What are the similarities and differences between the amygdalofugal tract and stria terminalis?
- Both project to septa region, hypothalamus, thalamus
- Sria terminalis has a much longer pathway
- Amygdalofugal pathway reaches the PAG and prefrontal cortex which the stria terminalis does not
What is this region of the brain?
Orbitofrontal cortex
What is the name of the notable neurons in the orbitofrontal cortex?
Error neurons
When do error neurons fire?
When there are differences between predicted and real outcomes (dopaminergic)
What is this?
Hippocampus
The orbitofrontal cortex is part of the…
Prefrontal cortex
What is the function of the orbitofrontal cortex?
Involved in assignment of values to certain actions and improves decision making as a subsequent trials are carried out by an individual.
What does the preservation of function when the orbitofrontal cortex is lesioned tell us?
as these roles are somewhat preserved with lesions to the area, there is likely a diffuse range of systems within the PFC that also help with the assignment of value, and previously learned values are likely retained
