Limbic System Flashcards
What functions are controlled by the Limbic system?
Use the mnemonic HOME: Homeostasis, Olfaction, Memory, Emotion.
Try to recall all of the structions considered to be part of the limbic system.
(Hint: There are at least 8 structures)
Amygdala, cingulate gyrus, fornix, hippocampus, (part of the) hypothalamus, mammillary bodies, nucleus accumbens, septal area, and a bunch of additional tracts and cortical regions.
What evidence suggests that the many structures of the limbic system are actually related?
Anatomic connections, similar physiology (eg density of cholinergic & opioid receptors), and behavioral associations.
Some conditions involve different structures of the limbic system simultaneously (eg herpes encephalitis and seizures).
What do the following tracts connect?
Fornix
Mammillothalamic
Perforant
Which of these are part of the Papez circuit?
Fornix connects the hippocampus and mammillary/septal nuclei.
Mammillothalamic connects the mammillary bodies and thalamus (big surprise).
Perforant connects the entorhinal cortex with the dentate nucleus of the hippocampus.
All of these participate in the Papez circuit!
What do the following tracts connect?
Stria Terminalis
Ventral Amygdalofugal Pathway
Medial Forebrain Bundle
Stria terminalis connects the amygdala with the septal region, nucleus accumbens, and part of the hypothalamus.
The ventral amygdalofugal pathway connects the amygdala with the brainstem posteriorly, and the septal nucleus and hypothalamus.
The medial forebrain bundle contains fibers from many different tracts; notes say “Hypothalamus, amygdala, and brainstem”
What are the symptoms of Kluver-Bucy syndrome?
What is the neurological basis for it?
What events can cause it?
Patients with Kluver-Bucy experience visual agnosia, placid affect, bulimia, increased oral activity, hypersexuality and hypermetamorphosis.
Lesions of the bilateral temporal lobes (involving the amygdala, hippocampus), resulting in loss of limbic connectivity.
Various encephalopathies, subarachnoid hemorrhages, Alzheimer’s/Pick’s diseases, a bilateral infarction…
What are the symptoms of interictal personality disorder?
What is its neurological basis?
What can cause it?
Patients with this disorder place high importance and signifiance on things in their lives, are preoccupied with philosophical or religious issues, experience hypergraphia to that goal, are socially viscous and hyposexual.
Interictal personality disorder appears to stem from hyperconnectivity of the limbic system of the temporal lobe.
Only temporal lobe epilepsy has been mentioned.
What are the “pleasure centers” of the brain?
What neurotransmitters are relevant there?
What drugs activate them?
The lateral hypothalamus and medial forebrain bundle. The nucleus accumbens also facilitates pleasure, so think “mesolimbic pathway” (includes part of the amygdala, hippocampus).
Catecholaminergic and dopaminergic signaling (eg block dopamine, block pleasure).
Drugs that enhance mesolimbic dopamine activity, eg Heroin and cocaine.
What stimulation/inhibitions can cause rage or pain?
Stimulation of the dorsomedial nucleus, or inhibition of the ventromedial nucleus.
Amygdala
What processes are controlled here?
What results from a bilateral lesion of this structure?
Amygdala
Fear reactions, attributing affect to visual stimuli, normal social interactions (including facial comprehension). “Integration of emotions, fear, and memory”.
Lesions cause reduced emotionality, lack of social comprehension.
Septal Area
What processes are controlled here?
What results from a bilateral lesion of this structure?
Septal Area
Sexual behavior.
Rage-like attacks and irritability. Curiously, damage also caused “increased sexual activity” and “enhancement of social contacts”
Hippocampus
What processes are controlled here?
Describe the hippocampal formation.
What results from a bilateral lesion of this structure?
Hippocampus
Formation of declarative memory (particularly episodic). In animals, responsible for spatial mapping (probably still true of humans).
Hippocampal formation consists of hippocampus, dentate gyrus, and subiculum. Afferent via the perforant pathway, efferent via the fornix.
Bilateral lesioning causes anterograde amnesia, but this varies depending on the nature of the lesion.
Distinguish between declarative and nondeclarative memory.
Distinguish between episodic and semantic memory.
Declarative can be explicitly recalled, nondeclarative is “implicit”, eg habituation, motor learning.
Episodic memory involves events. Semantic involves facts.
What can cause memory disorders?
Which of these are known to cause retrograde amnesia?
Dementia, head trauma, stroke (usually MCA), and Wernicke-Korsakoff’s psychosis.
Wernicke-Korsakoff’s syndrome (thiamine deficiency due to chronic alcoholism causing mammillary/thalamic lesions) is associated with anterograde AND retrograde amnesia, as well as ataxia, confusion, etc.
Cingulate Cortex
What processes are controlled here? Be specific.
What pathologies are associated with the cingulate cortex?
Cingulate Cortex
The anterior cingulate cortex controls emotion and motor function. The posterior controls visuospatial and memory functions.
Overactivity in the anterior cingulate cortex: OCD, Tourette’s syndrome
Diminished activity in the anterior cingulate cortex: Sociopathy, Akinetic mutism, contralateral motor neglect, emotional blunting and hypoalgesia.
