Limbic system Flashcards
What is the limbic system?
Several functionally and anatomically interconnected brain structures that are concerned with emotions and memories
What are the components of the limbic system?
- amygdala
- hypothalamus
- parahippocampal gyrus
- cingulate gyrus
- hypothalamus (mammillary bodies)
- orbital and medial PFC (orbitofrontal cortex)
- BF (nucleus accumbens, parts of basal ganglia)
- some thalamic nuclei (anterior dorsomedial)
- septal nuclei; insula
What is the cingulate gyrus?
Curved fold covering the corpus callosum
What is the parahippocampal gyrus?
Grey matter cortical region of the brain that surrounds the hippocampus
What is the Papez circuit?
Hippocampal formation → fornix → mammillary bodies → mammillothalamic tract → anterior thalamic nucleus → cingulum → entorhinal cortex → hippocampal formation
What does the amygdala consist of?
Three main groups of nuclei:
- Centromedial - visceral responses
- Cortical - forming part of the olfactory cortex
- Basolateral - emotional response to stimuli
Discuss inputs to the amygdala
They are to the basolateral and central nuclei
They are from:
1. All sensory association cortex (also direct sensory input from thalamus) - thus direct and indirect inputs from thalamus to amygdala
2. Cortical amygdala (part of primary olfactory cortex) - olfactory stimulation activates the amygdala
and frontal cortex
3. Entorhinal cortex, hippocampus (memory)
4. Cingulate (conscious emotional experience - feeling; top-down
control), prefrontal (reward-processing; top-down control), septal
(reward and reinforcement) areas
5. Mediodorsal thalamus (memory)
6. Brainstem - visceral sensory
Outputs from the amygdala
- One is direct to the hypothalamus (for autonomic and endocrine
components of emotional responses), called the ventral
amygdalofugal pathway – this is the primary output for the
basolateral and central nuclei - The other is via the stria terminalis a long looping path that
courses over diencephalon to terminate in the septal region and
nucleus accumbens (also projects to hypothalamus) – the primary
output for the medial nuclei
What is the amygdala responsible for?
- Processing the social signals of emotions (eg. fear)
- Facial expressions as well as vocal expressions - Emotional conditioning (fear conditioning)
- Consolidation of emotional memories
- Usually enhanced memory for emotional aspects of stories compared with non-emotional ones - Actual feeling of fear?
5 OLFACTORY PROCESSING → distinguishes the intensity of odours
What part of the limbic system distinguishes pleasant and unpleasant odours and projects back to the amygdala?
Orbitofrontal cortex
What structures is the amygdala therefore linked ti?
olfactory system, association cortex, hypothalamus and brainstem (via
amygdalofugal tract and stria terminalis)
What does the hippocampus consist of?
Cornu Ammonis - CA1-4
Dentate gyrus
What is the hippocampal formation?
Hippocampus – Dentate gyrus – Subiculum – Entorhinal cortex (in parahippocampal gyrus) See diagram on OneNote
Hippocampal inputs
All association cortex via entorhinal cortex
(perforate path)
Cingulate gyrus via cingulum
Septal cortex (ACh) and hypothalamus via fornix
Amygdala
Hippocampal outputs
The mammillary bodies, septum and hypothalamus via the fornix
- The fornix is the main output tract of the hippocampus and follows a C shaped curve caused by cortical expansion in development.
- The fornix also carries cholinergic fibers from the basal forebrain to the hippocampus, which degenerate in Alzheimer’s.
The association corticies via the parahippocampal gyrus
The Nucleus accumbens via the limbic striatum
The hippocampal commisure connects the two hippocampi