Where is the limbic system found?
Rim of cortex surrounding the corpus callosum and diencephalon
What is the limbic system composed of?
The limbic cortex and related subcortical nuclei
What are the two ‘subsystems’ of the limbic system?
Hippocampus and amygdala
What are the components of the limbic system?
Hippocampus, parahippocampal gyrus (entorhinal cortex), cingulate gyrus, septal region, and amygdala
What is the parahippocampal gyrus?
Major junctional region between the cerebral neocortex and allocortex of the hippocampal formation
What is the entorhinal cortex?
Brodmann Area 28
The anterior portion of the parahippocampal gyrus
What does ‘neocortical’ mean?
Afferent and efferent connections with association cortex areas
What does ‘allocortical’ mean?
Afferent and efferent connections with the hippocampal complex
What are the three regions of the hippocampal complex?
Subiculum, hippocampus proper, and dentate gyrus
What is the principle cell of the dentate gyrus?
Granule cells
What is another name for the hippocampus proper?
Cornu ammonis
How many subdivisions are there of the hippocampus proper?
4 subdivisions (CA1-4)
What is the principle cell of the hippocampus proper?
Pyramidal
What are the parts of the hippocampal cortex?
Subiculum and entorhinal cortex
What is the principle cell of the hippocampal cortex?
Pyramidal
Where do hippocampal afferents from the association cortex go?
Unimodal and multimodal association cortices -> Entorhinal cortex and subiculum -> Dentate gyrus
Where do afferents from the amygdala go?
Hippocampus proper/subiculum
Which hippocampal regions modulates emotion of memory?
Hippocampus proper/subiculum
Where are the modulatory inputs to the hippocampus from? Which neurotransmitters do they utilize?
Septal nuclei (ACh) -> fornix
Locus coeruleus (NE) Raphe nuclei (5-HT) VTA (DA)
Where do the hippocampal efferents from the subiculum go?
Subiculum -> Entorhinal cortex -> Association cortex
Subiculum -> Fimbria/fornix -> Septal nuclei, ventral striatum, thalamus, mammillary body
What is the role of the mammillary body in memory?
Autonomic component of emotional memories
What are the functions of the hippocampus?
Declarative long-term memory formation
- Long-term potentiation
- More calcium = stronger potentiation
Spatial memory and navigation
- Place cells
What diseases are associated with hippocampal damage?
Aging (senile dementia), Alzheimer’s disease, and Temporal lobe epilepsy (treatment could be removing hippocampus)
What was done to Patient HM? What was the result?
Bilateral medial temporal lobectomy for intractable epilepsy
Severe anterograde amnesia (inability to form new episodic memories)
What is the amygdala? Where is it located?
Collection of about a dozen nuclei lying beneath the limbic lobe
Anterior end of hippocampus and inferior horn of lateral ventricle
How is the amygdala divided?
Medial, central, and basolateral nuclear divisions
What is the function of the amygdala?
Emotional responses, primarily ones associated with fear
Roles in food seeking and sexual behaviours
What are the three types of sensory info carried by amygdala afferents?
- Sights, sounds, touch, smell, and taste
- General sense of physical/emotional comfort/discomfort
- Visceral sensory inputs (i.e., cardiac)
Where do the basolateral complex afferents of the amygdala come from? What type of afferents are they?
LGN (visual), MGN (auditory), and VPN/VPL (somatosensation)
Subcortical
Where do the afferents of the amygdala central nucleus come from? What type of afferents are they?
Visceral sensory inputs, hypothalamus, brainstem nuclei
Subcortical
Where do cortical inputs to the amygdala arrive?
Cortical inputs arrive at the basolateral complex before being distributed to other regions
Which unimodal sensory association areas project to the amygdala?
V4: object/face recognition
V5: motion detection
Which association cortices project to the amygdala?
Orbital cortex
Anterior cingulate cortex
Insula
Where do amygdala efferents go to? Which function are these corresponding to?
PAG to medulla/raphespinal tract - Antinociception
PAG to medullary reticulospinal tract - Freezing (defense reaction)
Locus coeruleus - Arousal/attention
NE medullary neurons to lateral grey horn - Tachycardia/hypertension
Hypothalamus/dorsal nucleus of vagus to heart - Bradycardia/fainting (due to strong emotion)
Hypothalamus - release corticotropin releasing hormone (stress)
Parabrachial (dorsal pontine) nucleus to medullary respiratory nuclei - Hyperventilation
Which functions are regulated by the amygdala?
Linking perception of objects and situations with appropriate emotional responses (esp. in danger)
Emotional aspects of learning (those associated with strong emotions are more likely to be remembered)
Phobias/anxiety
What is the result of bilateral amygdala damage?
Decreased aggression
Impaired ability to learn or remember the appropriate emotional and autonomic responses to stimuli
What is bilateral temporal lobe damage?
Removal of temporal lobes back to the level of the primary auditory cortex
Loss of amygdala, most of hippocampus, and parahippocampal gyrus
Which disorder is associated with bilateral temporal lobe damage? What are the effects?
Klüver-Bucy syndrome
Fearless and placid, absence of emotional reactions
Hypersexuality
High degree of attention to sensory stimuli