Flashcards in Limbic Deck (21)
Describe the Papez circuit.
See diagram slide 4.
Originally described in CNS areas thought to be involved in emotion; expanded to include amygdala, hypothalamus, prefrontal and associational cortices.
cingulate gyrus sends info to hippocampus which sends info about emotional expression to mammillary body of hypothalamus via fornix (huge fiber bundle)
also sends info to amygdala which then sends info to hypothalamus
hypothalamus sends info to prefrontal cortex
mammillary body of hypothalamus sends info to anterior nucleus of the thalamus via mammillothalamic tract
ant. nucleus of thalamus talks to cingulate gyrus
emotional experiences are input to cingulate gyrus, and association cortex receives/sends into to and from cingulate gyrus
Describe the amygdala structure and location.
is a collection of about a dozen nuclei lying beneath the uncus of the limbic lobe, at the anterior end of the hippocampus and the inferior horn of the lateral ventricle - is very closely associated with the uncus and the parahippocampal gyrus. The nuclei are subdivided into a medial, central, and basolateral group.
Describe the medial nuclei of the amygdala.
are interconnected with the olfactory system and are relatively small in humans
Describe the central nuclei of the amygdala.
small but their interconnections with the hypothalamus and related brainstem nuclei (PAG) are important in emotional responses
Describe the basolateral nuclei of the amygdala.
largest part of the human amygdala, are in some ways like a cortex without layers; they contain pyramidal neurons, are continuous with parahippocampal cortex, and are extensively interconnected with other cortical areas. Projections from the basolateral nuclei to the central nuclei provide a key link between the experience of emotions and their expression
Diagram the input/output of the nuclei of the amygdala.
See slide 6.
Sensory cortex and sensory thalamus go to lateral nucleus which feeds into the basal nucleus, accessory basal nucleus and the central nucleus directly
(basal nucleus and accessory basal also feed into the central nucleus)
central nucleus projects to hypothalamus, midbrain, pons, and medulla
main and accessory olfactory bulb projects to medial nucleus which then projects medial basal forebrain and hypothalamus
Describe the input to the amygdala.
How does olfactory info arrive?
How do physical and emotional comfort/discomfort reach the amygdala?
Where does visceral info come from?
Much of the input to the amygdala concerns sights, sounds, touches, smells, tastes.
olfactory info arrives at medial nuclei directly from the olfactory bulb and from the olfactory cortex.
The rest reaches the basolateral nuclei from the thalamus and from unimodal visual, auditory, and somatosensory and gustatory association areas.
A second kind of sensory input, dealing in a more general sense with levels of physical and emotional comfort and discomfort, also reaches the basolateral nuclei from orbital, anterior cingulate, and the insular cortices.
Visceral sensory inputs reach central nuclei from the hypothalamus and brainstem sites such as the PAG and parabrachial nuclei.
Describe the outputs of the amygdala.
primary, unimodal sensory cortex, anterior limbic cortex, ventral striatum, thalamus (dorsomedial nucleus), hypothalamus, brainstem visceral nuclei, hippocampus
-Fibers leave the amygdala through the stria terminalis and the ventral amygdalofugal pathway to reach many of the same areas that send afferents to it (septal nuclei & hypothalamus, olfactory regions, orbital & anterior cingulate cortices).
-Some reach the ventral striatum, which in turn projects to the ventral pallidum.
-The ventral striatum and pallidum are links in a basal ganglia circuit that projects to the dorsomedial nucleus of the thalamus and influence prefrontal and orbital frontal cortex.*
Many ventral amygdalofugal fibers turn dorsally in the diencephalon and reach the dorsomedial nucleus of the thalamus.
Finally, some amygdalar efferents pass directly to extensive cortical areas in the temporal lobe and beyond. Some reach the hippocampus and related cortical areas, while others extend all the way to primary sensory areas.
What did bilateral lesions to the tips of temporal lobes, originally done to relieve intractable seizures, result in?
a constellation of deficits called Kluver-Bucy syndrome:
1. Docility (diminished fear response, unusually low aggression reactions. placid, tame)
2. Dietary changes or Hyperphagia! (eating inappropriate things or overeating)
3. Hyperorality - tendency to put everything in the mouth
4. Hypersexuality - heightened sex drive or seek sexual stimulation from unusual or inappropriate objects
5. Visual agnosia -inability to recognize familiar objects or people
Where do efferents from the amygdala primarily terminate?
dorsomedial nucleus (thalamus)
Describe the hippocmapus. What is it made up of? Where is it?
a distinctive area of cerebral cortex folded into the temporal lobe (sea horse shape)
made up of the dentate gyrus and the hippocampus proper (two interlocking strips of three-layered cortex) together with the subiculum (a transition zone between the hippocampus proper and temporal lobe neocortex).
How many layers does the hippocampus have? Cerebellum?
Hippocampus is a 3 layered subcortical structure (NOT 6)
Cerebellum also has only 3 layers.
Describe the anterior part of the parahippocampal gyrus?
The anterior part of the parahippocampal gyrus (entorhinal cortex) is the major interface between the hippocampus and vast areas of association cortex, allowing the hippocampus to serve as a key link underlying declarative memory.
What would bilateral damage to the hippocampus and neighboring areas of cortex, or to the diencephalic areas they are interconnected with, cause?
Bilateral damage to the hippocampus and neighboring areas of cortex, or to the diencephalic areas they are interconnected with, causes anterograde amnesia, in which new memories for facts and events cannot be formed. Retrograde amnesia following such damage is limited to a few hours our days, indicating that long-term memories mostly live outside the hippocampus.
(but hippocampus is important for knowing where that info is stored so large lesions will affect long term memory eventually)
Describe the inputs to the hippocampus.
Inputs to the entorhinal cortex, and from there to the hippocampus, come from widespread unimodal, multimodal, and limbic cortical areas.
In addition, modulatory cholinergic inputs from the septal nuclei* reach the hippocampus directly by traveling "backward“ through the fornix, which is a major output route from the hippocampus (MB).
Finally, there are direct projections from the amygdala to the hippocampus (the amygdala is important for marking the emotional significance of situations and events); this connection affects the probability that something will be recorded as a declarative memory, depending on our emotional reaction to it.
Describe the outputs form the hippocampus.
The hippocampus projects back, by way of entorhinal cortex, to widespread unimodal, multimodal, and limbic cortical areas.
Hippocampal outputs also reach limbic cortex indirectly, by way of projections to the mammillary bodies through the fornix.
The fornix curves around with the lateral ventricle; it separates from the hippocampus near the splenium of the corpus callosum, travels forward along the inferior edge of the septum pellucidum, turns downward in front of the interventricular foramen, and enters the hypothalamus. The mammillary bodies project to the anterior nucleus of the thalamus through the mammillothalamic tract, and this link forms part of the Papez circuit.
Describe the clinical consequences of damage to hippocampal targets.
(mammillary nuclei of the hypothalamus)
Massive input from hippocampal formation via the fornix.
Sends unilateral, collateral projections to: thalamus (via mammillothalamic tract), midbrain tegmentum, and reticular nuclei associated with cerebellum/vestibular inputs.
Unique in hypothalamus in that mammillary n. have highly restricted inputs/outputs
Critical for spatial memory/position of head in space.
Describe the clinical consequences of damage to hippocampal targets.
Disabling degenerative brain disorder. Lack of thiamine (vitamin B1) due to alcohol abuse, dietary deficiencies, prolonged vomiting, eating disorders, or the effects of chemotherapy.
Symptoms: mental confusion, confabulation, attention deficit, memory impairment (both anterograde and retrograde), vision impairment, stupor, coma, hypothermia, hypotension, and ataxia.
Wernicke’s encephalopathy represents the “acute” phase of the disorder;
Korsakoff’s Amnesic Syndrome represents the “chronic” phase (memory disorder, confabulation).
Describe the septal nuclei.
Afferents: Hippocampus, Amygdala & Preoptic area of hypothalamus
Efferents: Hippocampus, Amygdala, Preoptic area of hypothalamus, Mammillary body & Median eminence
• Regulates gonadal hormone secretion and various reproductive and sexual behaviors by way of its gonadotropin-releasing hormone projections to median eminence.
What does septal nuclei facilitate?
What would lesions produce?
• Facilitates memory formation via its massive cholinergic projection back to the hippocampus.
• Lesions in animals produce septal syndrome of general behavioral overreaction, particularly evident as "septal rage" after trivial stimulation.