Limbic syguvyig8yvuiyuybuby iyiyhistem.pptx

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1. Limbic system Dr.Sakshi Ghodke.

2. Limbic: of limbus (Latin) , meaning border or margin  initially meant to demarcate the border between the cortex and the brainstem also called the paleo-mammalian cortex, located on both sides of the thalamus, immediately beneath the temporal lobes

3. LIMBIC STRUCTURES hippocampal formation limbic cortex amygdaloid nucleus hypothalamus anterior thalamic nuclei mamillary bodies

4. Hippocampus: curved elevation of gray matter that extends throughout the entire length of the floor of the inferior horn of the lateral ventricle, covered by a thin layer called the alveus The alveus consists of nerve fibers originating in the hippocampus, which converge medially to form a bundle called the fimbria  continuous with the crus of the fornix Dentate gyrus: narrow, notched band of gray matter that lies between the fimbria and the parahippocampal gyrus. Anteriorly, the dentate gyrus is continued into the uncus . Subicular complex: incl. presubiculum , parasubiculum , and the subiculum  transition regions between the hippocampus and the parahippocampal gyrus

5. Cingulate gyrus: closely related to corpus callosum Habenula: hub for limbic, basal ganglia, brainstem circuits Parahippocampal gyrus: includes many regions, incl. the entorhinal cortex

6. AMYGDALOID NUCLEUS 1.Basolateral nucleus: acts like neocortex, CB1 positive 2.Olfacfory nucleus 3.Centromedial nucleus: connects with hypothalamus, CB 1 negative

7. hypothalamus Regulates emotional, autonomic, endocrine, and somatic responses ventromedial nucleus: reproductive, ingestive behaviour Lateral nucleus: concerned with feeding and wakefullness . It is the feeding Centre . mammillary bodies: lateral + medial mammillary nuclei receive hippocampal input through the fornix  project to the anterior thalamic nuclei

8. functional circuits Intrinsic circuitry: components of the limbic system are interconnected and information is projected via the fornix: anterior thalamus  limbic system hypothalamus and septal area  brain stem, spinal cord

9. Cortico-limbic circuitry: information from association regions of temporal and prefrontal cortices projects to the amygdala. Output from the amygdala is relayed via two main pathways: the dorsal stria terminalis  septal area, hypothalamus the ventral amygdalofugal pathway  septal area, hypothalamus, medial dorsal thalamic nucleus  feedback to neocortical regions

10. 3.Amygdalofugal pathway: projects to nucleus accumbens in the ventral striatum  ventral pallidum  medial dorsal thalamus  feedback to neocortical regions

11. 2.Appetite and eating behaviours ● Amygdala- food choice and emotional modulation of food intake. ● The lateral nucleus of the hypothalamus - feeding center. ● The ventromedial nucleus -satiety center.

12. 3.Sleep and dreams : ● The suprachiasmatic nucleus of hypothalamus is the circadian rhythm generator controlling the sleep-wake cycle. ● Ventrolateral Preoptic Nucleus -Inhibition of major arousal mechanisms functions as a “sleep switch “ - Promoting sleep. ● The lateral hypothalamic area (LHA) -Promote wakefulness.

13. 4.Emotional responses FEAR ● Fear responses are produced by the stimulation of hypothalamus and amygdala. ● Amygdala abolishes fear and its autonomic and endocrine responses , also involved in fear learning. RAGE AND PLACIDITY : Destruction of the ventromedial nucleus of hypothalamus and septal nuclei in animals may induce rage. Bilateral destruction of amygdala results in placidity.

14. 5.Sexual Behaviour : ● Female sexual behaviour: Glutaminergic input from the medial amygdala( MeA ) and The bed nucleus of the stria terminalis(BNST) ● Male Sexual behaviour: Medial preoptic area of the hypothalamus.

15. 6.reward and motivation

16. memory Hippocampus + Parahippocampal gyrus short term, working memory conversion of new memories into long term explicit, semantic memory amygdala + prefrontal cortex + MTL emotional memories fearful memories; acquisition, extinction, and recovery of fears

17. psychiatric implications

18. Dementia: Degenerative changes in the limbic system-Pick's disease and Alzheimer's disease. ● Marked atrophy is found in the limbic system, most notably the dentate gyrus and hippocampus. ● Alzheimer's disease-senile plaques and neurofibrillary tangles in hippocampus and amygdala

19. Anxiety disorders ● Amygdala hijack Fear circuitry- Involving amygdala, prefrontal and anterior cingulate. ● Anxiety disorders may be the result of a failure of the anterior cingulate and hippocampus to modulate the activity of the amygdala.

20. schizophrenia Overactivity of mesolimbic dopaminergic pathway  positive symptoms reduced hippocampal size basolateral circuit involvement  social cognition defects reduced GABAergic neurons in anterior thalamus, cingulate gyrus  glutamatergic excitotoxicity

21. kluver-bucy syndrome B/L destruction of amygdaloid complex placidity visual agnosia hyperorality hypersexuality can be caused by: trauma infections degenerative diseases CVA

22. autism Disproportionate involvement of areas associated with social cognition and affective processing – amygdala (basolateral)

23. temporal lobe epilepsy causes: hippocampal sclerosis mesial temporal sclerosis (hippocampus + parahippocampal gyrus + amygdala)

24. limbic encephalitis paraneoplastic syndrome 2° to CA lung, breast, etc. anti-Hu, anti-GAD, anti- AMPAr manifests as subacute onset memory loss, agitation, confusion, psychosis, recurrent seizures refractory to treatment

25. Korsakoff’s psychosis damage to diencephalic memory system (mamillary bodies, anterior thalamic nuclei) chronic prominent anterograde + retrograde amnesia immediate recall usually preserved confabulation – not pathognomonic

26. TAKE HOME MESSAGE the limbic system represents a phylogenetically ancient part of the brain concerned with fear , flight/fight responses , preservation of self ( appetite and feeding behaviour ) and preservation of species ( sexual behaviour ) it plays a major role in learning and consolidation of new memories disorders affecting the limbic system may share common features suggesting distortion of normal function – incl. memory loss and abnormal affective responses