T h e L i m b i c S y s t e m

Presenter: Dr. M. Hemalatha

Moderater: Dr.V. Sharbandhraj

Over view of presentation

• History

• Anatomy

• Histology

• Functional circuitry

• Functions of the limbic system

• Clinical implications

History• Paul broca applied the term limbic(latin-border)to the

curved rim of cortex includes CG,PHG-b/n-diencephalon and cerebral hemespheres

• James papez postulated on basis-anatomical data cortical regions linked hippocampus mammilary body and thalamus.

• This concept supported by kluver & brucy who showed temporal lobe lesion which disrupts components of the circuit.

• Paul maclean coined term LYMBIC SYSTEM to describe brocas lmbic lobe and related sub cortical structures in relation to emotions

Components of limbic system

Components of limbic system

1. Limbic lobea) cingulate gyrus

b) parahippocampal gyurs

2. Hippocampal formationa) dentate gyrus

b) hippocampus

c) sibicular complex

3. Amygdala

4. Septal area

5. Hypothalamas

Others - cortex and insula,uncus,sriaterminalis

It is functional anatomical system interconnecting - cortical and sub cortical structures.

ANATOMY & HISTOLO The Cingulate gyrus

• Located dorsal to corpus callosum

• Includes several cortical regions that are heavily interconnected with the association areas of the cerebral cortex

• Posteriorly, it becomes continuous (via bundle of fibresin the white matter-cingulum) with the parahippocapal gyrus.

The Parahippocampal gyrus

• Located in medial temporal lobe

• Lies between the hippocampalfissure and the collateral sulcus

• Continuous with the hippocampus along with the medial edge of the temporal lobe

• Cortical structure of parahippocampal gyrus is six layered.

The Dentate gyrus• -Narrow notched band of gray

matter

• -Lies between fimbria of the hippocampus and the parahippocampal gyrus

• -Anteriorly– contunued into the uncus

• -Posteriorly– continuous with indusium griseum

-three layers–outer acellular molecular,middle granular inner polymorphic layer.

The hippocampus• Curved elevation of gray matter

• Extends entire length of the floor of the inferior horn of the lateral ventricle

• anterior end --- pes hippocampus

• Terminates posteriorly– beneath the splenium of corpus callosum

It is divided into FOUR distinct fields–CA1, CA2 and CA3 ,CA4(CA=Cornuammonis)

Alveus– thin layer of white matter adjacent to the poly morphic layr of hippocampus

• The hippocampus has-

• outer molecular-

• middle pyramidal-

• Inner polymorphic

subicular complex

Includes pre, para, and subicular parts

The transition region b/n hippocampus and parahippocampal gyrus

The amygdala• Located in medial temporal lobe

• Just anterior to the hippocampalformation

• It is fused with the tip of the tail of the caudate nucleus

• Stria terminalis emerges from its post aspect

• It is a group of nuclei larger basolater, smaller centromedial

• Centromedial amygdala appears to be part of a larger structure that is continuous through the sublenticularinnominate with bed nucleus of striaterminalis(extended amygdala)

septal area

• Gray matter structure located immediately

above the anterior commissure-projects to habenular nucei via

stria medullaris thalami and ant hypothalamus.

Insula

Medial cortical gyrus located between the amygdala and the frontal lobe

Formed by the amygdala and the rostral hippocampus

Uncus

The entorhinal cortex

• Located in the anterior part of the parahippocampal gyrus, on medial surface of temporal lobe

• Transition zone between hippocampus and temporal neocortex

The hypothalamus

• Lies at the centre of the limbicsystem

• It is a confluence of many neural pathways

• Devided-anterior to posterior 3 zones

Supraoptic region

Tuberal region

Mammillary region

3 zones devided by fornix in to medial and lateral

areas

The lateral and medial mamillary nuclei receive hippocampal input through fornix and project to the anterior nucleus of thlamus

Limbic spindle cells(Von Economo)–20 times more in humans than apes--- concentrated in ant cingulate gyrus, prefrontal cortex, the insula

- central to governance of social emotion and moral judgement

Mirror cells– more developed in humans thanin primates-reside in insula, ant cingualte

- mediate empathy– the experience of feeling the emotions of another

Connections of the limbic system

• The major structures of limbic system are interconnected with each other and with other components of nervous system in various ways.

In generel, it is area of intimate processing between hypothalamus and cortical information processing

The connecting pathways of limbic system are– the alveus, the fimbriae, the fornix, the mamillothalamic tract, and the striaterminalis

Neurotransmitter system in limbic system include– dopamine, serotonin, noradrenergic, and cholinergic systems

PAPEZ CIRCUIT

PAPEZ CIRCUIT

Hippocampus conectionsmajor inputs---layers 2 &3 of ERC

septal & hypothalamic fibersvia fornix

few from c/L hippo campal formation

glutaminergic fibers frm –

fimbria

Hippocapal efferents

Circuits of amygdala

Functions of the limbic system • The Ls is involved in behaviour required for self-preservation

and the preservation of species

control over behaviour regulated by hypothalamus and brainstem, Plays a role is sexual behaviour, Has special role in memory

Part Function

Amygdala AGGRESSION and FEAR

Cingulate gyrus AUTONOMIC FUNCTION

Hippocampus RECENT MEMORY

Hypothalamus ENDOCRINE FUNCTION

Mammillary body LONG MEMORY

Nucleus accumbens ADDICTION

Prefrontal area PERSONALITY

Parahippocampus SPATIAL MEMORY

Amygdala and ERC are closely related olfactory cortex-role in processing of olfactory sensations.

Amygdala-involves in emotional response to smellERC- concerns with olfactory memories

Olfaction:

FEAR: -response- produced by stimulation- amygdala and

hypothalamus- amygdala involves in fear learning- imaging studies -viewing fearful faces stimulates leftamygdala

damage-abolishes fear

EMOTIONAL RESPONSES

Appetite and eating behaviors:

Amygdala –food choice and emotional modulation of food intake

Hypothalamus:LN-centre for control of feedingVMN-functions satiety centre

stimulation of the anterior cingulate & hypothalamus triggers -ANSExcessive stimulation- amplification of emotions and motor responses and may lead to anxiety, tics, impulsivity, and OCD. Inhibition leads to akinetic mutism,Post cingulate is important for visual spatial memory functions

Autonomic endocrine responses

Rage and placidity:

- feeing of intense,violent or growing anger,associated

with fright or flight response.

- when faced with thretening situations hypotalamus

releases harmones rapidly-rage

- destruction of VM hypothalamic and septal nuclei intact

cerebral cortices –rage

- B/L damage amygdala-placidity

- VM is destroyed after amgdala-placidity converted to rage

Sleep and dreams

• PET,fMRI-shown LS is most active brain area in processing of dreaming.

• LS-ties emotions and memory during REM to form content of dreams.

• SCN Hypothalamus - cercadian rhythem generation-controls sleep-wake cycle

• -GABAnergic,glutaminergic neurons- -VLPO-inhibits major arousal meconsms-promotes sleep

• Lateral hypohalamic area-Orexinergic neurons –that promotes-wakefulness by inhibting VLPO,REM promoting thalamic nuclei- PPT-LDT.

Social cognition:

- cingulate gyrus , basolateral amygdala are involved

-- involves unerstandng and dealing with other people

-- involves functioning regions that mediates-face perception, emotional processing ,self referense and working memory-support the complex behaviors for social interactions

Sexual behavior

Sexual behavior

• MPOA- hypothalamus –key stucture in control of male sexual behavior,

• Dopamin triggers penile erection by acting on oxytocenergic neurons in the PVN of hypothalamus

• The inhibition of these neurons by GABA and its agonists,opioid like drugs inhibits sexual response

• Glutaminergic inputs from Medial amygdala and bed nucleus stria terminalis - MPOA-mediates female stimulated increased dopamin –enhances copulatoryability,^ glutamate –MPOA- facilitate copulation and genital reflexes during ejaculation

memory

Emotional memory:emotion has power ful influence on learning and memory

Amygdala ,prefrontal cortex, medial temporl lobe-consolidation,retrival of emotional memories

Amygdala,prefrotal cortex, and hippocampus-acuisition,extinction and recovery of fears to cues

Hippocampus –critical for recent , declaratie memory

Medial temporal lobe memory system:

hippocampus ,adjecent cortex,para hppocampal region and enterorhinal perirhinal regions--storage of new memories

Diencephalic memory system:hypothalamus,mammilarybody,DM neucleus of thalamus-storage of recent memory

--dysfunction of circuit-korsakoffs syndrome

Addiction and motivation

• Reward circuitry under lying addictive behavior includes amygdala and nucleus accumbens

• Amygdala plays acentral role in cue induced relapse.relapseis associated with cues, stress and single dose of drug abuse results in release of excitatory neuro transmitters in hippocampus and amygdala

• The pathway of motivated behavior involves the prefrontal cortex,ventral tegmental area,amygdala,nucleusaccumbense involved in motivation to take drugs of abuse and compulsive nature of drug taking.

CLINICAL IMPLICATIONS

• TEMPORAL LOBE EPILEPSY—mc-hippocampal sclerosis hippocampal sclerosis+amygdala+parahppocampal gyrustermed –MTS-its not limited to medial temporal lobe also a LS-disorder

• Limbic encephalitis-paraneoplastic syndrome – with

Ca lung,breast.

- mecnsm of disease not known-involves hippo,amygdala,cingulate gyrus,insula OFC

-pts develops subacute memory loss,dementia,invluntorymovements and ataxia

Alzhiemers dementia• Gross– medial temporal lobe atrophy and hippocampal

atrophy most common

• Plaques and tangles most frequently present in hippocampaland entorhinal cortex

• Hippocampal damage-antegrade amnesia

Hypofunction and hyperfunction of some anterior limbic areas---prefrontal regions and sub cortical structures-thalamus,striatum,amygdala

BPAD

Korsakoffs psycosis

• Caused by B1 deficiency-damage periventricular areas: medial thalamus, hypothalamus, mamillary bodies,reticularformation

• Lesions show petechial hemorrhages, edema, myelin loss, and reactive gliosis. Neurons generally preserved.

• Recent memory is more disturbed than remote memory,immediate recall is preserved.

Limbic epilepsy-amygdala, hippocampus, ERC, cingulate or OFC

• fear, déjà vu, jamais vu, elementary and complex visual hallucinations, illusions, forced thinking, or emotional distress.

• Anxiety disorders-may be result -failure of ant cingulate, hippocampus to modulate amygdala

• Bilateral destruction of amygdala and inferior temporal cortex

agnosia,placidity,hyperorality,hypersexuality

• Causes: cerebraltruma,herpis encephalitis, infections alziemers dementias and other dementias,neimanpicks disease &CVdiseases

Kluver-bucy syndrome

schizophrenia

• Various addictive compounds affect the dopamine transmission in nucleus accumbens ( ventral striatum or (mesolimbic) and frontal cortical (mesocortical) systems.

• these pathways functionally unbalanced in patients with schizophrenia.

• pts - schizophrenia -diminished dopamine effects through mesocortical systems to the prefrontal cortex. Produce negetive symptoms .

• increase in dopamine effects via the mesolimbicsystem to the ventral striatal system, resulting in positive symptoms

ADHD

• Enlarged hippocampus - children and adolecents in response to disturbances in perception of time,temporal proccessing and stimulus seeking associated with ADHD.

• Disrupted connections b/n amygdala & orbitofrontal cortex may contribute behavioral disinhibition in people with ADHD

Autism and aspergers syndrome-

cingulategyrus,amygdala (BLcircuit) mediates cognitiveand affective processing-dysfunction leads -ASD

References

• Kaplan and saddock’s comprehensinve textbook of psychiatry

• Lishman, organic psychiatry

• Adams & victor neuroanatomy

• Lymbic system by E. Mohan das

• Internet