Limbic system final

important topic

1. Dr. A mruta Rajamanya Dnb N eurology Trainee KMC Mangalore Limbic System

2. HISTORICAL ASPECTS OF LIMBIC SYSTEM

3. THE BROAD FUNCTIONAL DIVISIONS Rostral limbic system : Amygdala, septum, orbitofrontal cortex , anterior insula, and anterior cingulate – Important for emotion Caudal system : Hippocampus , posterior parahippocampal cortex and posterior cingulate – Important for memory and visual-spatial functions

4. limbic lobe V/S limbic system Limbic lobe (Cortical areas of the limbic system) Limbic system (Limbic lobe+ Nuclei +connection) Parahippocampal gyrus • Hippocampus • Orbitalfrontal . • Cingulate gyrus • Insula • Nuclei: – Amagdyla – Septal nuclei – Mammillary body – Anterial thalamus • Connection: – Fornix – Median forebrain bundle – Stria terminalis – Mamillothalamic tract

5. COMPONENTS OF LIMBIC SYSTEM Olfactory pathways Anterior perforated substance Pyriform lobe Septal area Amygdaloid body Limbic cortex Hippocampal formation Elements of diencephalon Bundles of axons connecting the above region

6. Olfactory Pathway

7.  Anterior perforated substance • Mass of gray matter on either side of optic chiasma • Perforated by central branch of MCA  Pyriform lobe • Uncus – Curved portion of anterior extremity of hippocampal gyrus • Principal region of awareness of olfaction • Primary olfactory area • Fibers from lateral olfactory stria terminate in it • Limen insulae – Cortex of most medial part of insula • Entorhinal cortex - Anterior part of parahippcampal gyrus

8.  Septal area • Situated ventral to corpus callosum • Includes paraterminal gyrus & septum pellucidam • Receive olfactory fibre from medial olfactory stria •Has reciprocal connections with hippocampus through fornix

9. Amygdala Almond shaped collection of nuclei Lies above inferior horn of lateral ventricle Embedded in uncus Window of limbic system: wide afferent connections with visual, auditory association areas. Wide efferent connections

10. Amygdala stimulation produces emotional behaviors through subcortical pathways

11. Functions of the Amygdala Behavioral awareness areas Project into the limbic system one’s current status in relation to both surroundings and thoughts. Make the person behavioral response appropriate for each occasion Relate environmental stimuli to coordinated behavioral autonomic and endocrine responses seen in species- preservation. Responses include: Feeding and drinking fighting behavior Mating and maternal care Responses to physical or emotional stresses

12. LIMBIC LOBE Situated at the inferomedial aspect of the cerebral hemispheres.  Consists of two concentric gyri surrounding the corpus callosum .  Broca proposed the larger outer gyrus -"limbic gyrus smaller inner one "the intralimbic gyrus ".  The limbic gyrus (limbic lobe) consists the isthmus of the cingulate gyrus , the parahippocampal gyrus the subcallosal area.

13. CINGULATE GYRUS Situated dorsal to the corpus callosum Heavily interconnected with the association areas of the cerebral cortex . Receives inputs from the anterior nucleus of the thalamus and the neocortex , somatosensory areas of the cerebral cortex. It projects to the entorhinal cortex via the cingulum . Involved with emotion formation and processing, learning, and memory ,central role in attention, feelings of safety and security have also been attributed to this part of the brain.

14. PARAHIPPOCAMPAL GYRUS Situated in the medial temporal lobe. Important role in memory encoding and retrieval. The ERC funnels highly processed cortical information to the hippocampal formation and serves as its major output pathway.

15. HIPPOCAMPAL FORMATION located in the temporal lobe as the floor of the inferior horn of the lateral ventricle. A curved and recurved sheet of cortex folded into the medial surface of the temporal lobe. S shaped in coronal section. It has 3 distinct zones: dentate gyrus , hippocampus proper , subiculum . Upper limb form hippocampus. Two parts – cornu ammonis & dentate gyrus Middle limb connects cornu ammonis with parahippcampal gyrus – subiculam Lower limb – parahippocampal gyrus

16. HIPPOCAMPUS In cross section resembles “sea horse ”  Is the inferomedial structure of the parahippocampal formation .  Hippocampus is divided into several zones of pyramidal cells:  CA1 – CA 4 fields  Trilaminate structure Molecular Pyramidal Polymorphic  The most sensitive area in the brain for Ischemic events in hippocampus is CA1.

17. • Strata within layers of hippocampus :- - Stratum oriens - Stratum pyramidalis - Stratum radiatum - Stratum lacunosum • Schaffer’s collaterals • Perforant pathway Trilaminar archicortex :-3 Distinct fields :-CA1,CA2,CA3 • CA3:- largest Pyramidal cells - receive mossy fibres • CA2 :-pyramidal cells -input from supramammillary region • CA1 :-most complex

18. DENTATE GYRUS Lies b/w fimbria of hippocampus& parahippocampal gyrus Toothed / beaded surface Consists of three layers of neurons: Molecular Granular-most prominent, contains granule cells, principal excitatory neurons of dentate gyrus Polymorphic The major input- perforant pathway from layer II of the entorhinal cortex The perforant pathway - medial perforant path - lateral perforant path Function- formation of memories play a role in depression.

19. SUBICULAR COMPLEX Subiculum is the transitional zone between the six-layered entorhinal cortex and the three-layered hippocampus three components : pre subiculum , para subiculum subiculum

20. FORNIX & FIMBRIA

21. Elements of diencephalon Hebenular nucleus- lies in hebenular triangle at the root of pineal body Anterior thalamic nucleus Afferent from – mamillary body Efferent to – cingulate gyrus Hypothalamus • The hypothalamus consists of only 4 cm3 of neural tissue , or 0.3% of the total brain.

22. Hypothalamus Relations  Anteriorly: • Extends up to lamina terminalis and merges with olfactory Structures.  Posteriorly : • Merges with ventral thalamus  Medial side: • Forms the wall of the third Ventricle  Laterally : • Contact with the internal capsule  Inferiorly: • Related to the structures of the third ventricle

23. HIPPOCAMPAL AFFERENTS Major input into the hippocampal formation arises from neurons in layers II and III of the entorhinal cortex . In addition, some septal and hypothalamic formation reach the hippocampal formation via the fornix Few fibers also arrive from contralateral hippocampal formation via the hippocampal commissure

24. FUNCTIONAL CIRCUiTARY OF LIMBIC SYSTEM

25. INTERNAL CIRCUITS Intrinsic connections of the hippocampus involve fibers from the entorhinal area, dentate gyrus , ammon’s horn and subiculum . The three primary pathways of this area are called the perforant pathway, mossyfibers and Schaffer collaterals. Existence of a fourth pathway, the alvear pathway, has been questioned, from the entorhinal area to ammon’s horn

26. Perforant path where glutamateric fibers from the entorhinal area perforate the subiculum and reach the dentate gyrus .  The glutamatergic mossy fibers then extend from the dentate gyrus to CA3 (pyramidal layer )  Many axons of CA3, however, give off the Schaffer collaterals that reach the dendrites of CA1 .  CA1 is considered the main output of the hippocampus with fibers extending to the alveus , fimbria and then fornix . 

27. EFFERENTS • Columns of fonix - septal area, ant part of hypothalamus, substantia Innominata • Lateral dorsal thalamic nucleus – thalamus – mamillary body – ant nucleus of thalamus • Mamillotegmental fasciculus

28. FUNCTIONS OF THE LIMBIC SYSTEM OLFACTION :  limbic structures are closely related to the olfactory cortex and have a role in the processing of olfactory sensation  Amygdala is involved in the emotional response to smell while the entorhinal cortex is concerned with olfactory memories

29. APPETITE AND EATING BEHAVIOUR :  Amygdala plays a role in food choice and emotional modulation of food intake . SLEEP AND DREAMS :  PET and MRI have shown that the limbic system is the most active brain areas during the process of dreaming.  Probably interweaves unconscious primal emotions with conscious cognitive thoughts  The suprachiasmatic nucleus of the hypothalamus generates the circadian cycle. Controls sleep-wake cycle.

30. EMOTIONAL RESPONSES :  FEAR: fear responses are produced by the stimulation of the hypothalamus and amygala . Amygdala is also involved in fear learning .  RAGE AND PLACIDITY: Rage reponses to minor stimuli are observed after removal of the neocortex . Destruction of the the ventromedial hypothalamic nuclei and septal nuclei also induces rage.

31. AUTONOMIC AND ENDOCRINE RESPONSES TO EMOTION :  Limbic stimulation causes changes in respiration and blood pressure .  The stimulation of the cingulate gyrus and hypothalamus can elicit autonomic responses  The fear and rage responses mediated by the limbic system cause stimulation of various parts of the hypothalamus, especially the lateral areas and produce diffuse sympathetic discharge. The massive sympathetic discharge during stress is called the — fight or fright response “.  Stress via cortical and limbic connections causes release of corticotropin -releasing hormone (CRH) from the paraventricular nuclei of the hypothalamus.

32. SEXUAL BEHAVIOUR:  The medial preoptic area of the hypothalamus is a key structure in the central control of male sexual behavior . Chemosensory efferents from the main and accessory olfactory systems project to the medial amygdala ( MeA )

33. REWARD AND PUNISHMENT : electrical stimulation of certain limbic area pleased or satisfies the animal or cause terror, pain, fear, defense , escape reactions Reward centers: along the course of the medial forebrain bundle and lateral and ventromedial nuclei of the hypothalamus Punishment centers: central gray area surrounding the aqueduct of sylvius in the mesencephalon and extending upward into the periventricular zones of the hypothalmus and thalamus

34. MEMORY :  Emotional memory : Amygdala is involved in consolidation and retrieval of emotional memories. also involved in the acquisition , extinction and recovery of fears to cues and contexts . Hippocampus is critical for long-term, declarative memory storage .  Medial temporal lobe memory system : include the hippocampus and adjacent cortex, the parahippocampal regions (PHG) . This memory system is involved in the storage of new memories  Diencephalic memory system : consists of thehypothalamus , mammillary body and the dorsomedial nucleus of thalamus. This circuit is important for the storage of recent memory; a dysfunction of this circuit results in Korsakoff’s syndrome.

35. SOCIAL COGNITION : refers to thought processes involved in understanding and dealing with other people .  Social cognition involves regions that mediate face perception, emotional processing; theory of mind (TOM); self-reference and working memory .  Together, the functioning of these regions would support the complex behaviors necessary for social interactions .  Limbic structures involved are the cingulate gyrus and amygdala

36. LIMBIC CLINICAL SYNDROMES

37. LIMBIC SYSTEM - CLINICAL IMPLICATIONS