limbic system by dr ali

PRESENTER:DR. MD. OSMAN ALI

The Limbic System

Scheme of presentation

Introduction AnatomyPhysiology Applied aspects

Case of Arthur Shawcross

What is limbic system?

It includes structures forming a border between hypothalamus and cerebral cortex.

It is simply

functional anatomic system of interconnected cortical and subcortical structures.

Parts of limbic system

Parts mostly listed are Limbic cortex—the cingulate and the

parahippocampal gyri The hippocampal formation– the dentate

gyrus, the hippocampus, the subicular complex.

The amygdala

The septal area

The hypothalamus, the related thalamic(ant) and cortical areas

Other parts included are--- insula, entorhinal cortex, nucleus accumbens

No unanimity exists on brain structures that constitute the LS

History of concept of the limbic system 1

Paul Broca– coined the term limbic(Le Grand Lobe Limbique)-- to include curved rim of cortex including cingulate and parahippocampal gyrus which was different from the rest of the cerebral mantle(appeared paler)(Broca’s cortex/lobe).

This cortex later shown to be composed of only three layers– labelled allocortex to distinguish it from the six layered eucortex that make up most of the cerebral mantle

History of concept of the limbic system 2

James Papez(1937)– postulated these cortical regions(the cingulate gyrus and the parahippocampal gyrus ) are linked to hippocampus, mamillary body and anterior thalamus in circuit that mediated emotional behaviour(Papez circuit)

Emotions tend to go round and round in this circuit

History of concept of the LS 3

Heinrich Kluver and Paul Bucy(1939)—by removing temporal lobes in monkeys they found that amygdala of temporal lobe has role in taming and other basic instincts– fighting, fleeing, feeding and sex

Kluver Bucy syndrome

History of concept of the LS 4

Paul Maclean(1952)--- coined the term limbic system to describe broca’s lobe and related subcortical nuclei as the neural substitute for emotion

History of concept of limbic system 5

Originally term limbic system encompassed only Broca’s cortex and Papez’s circuitry and later amygdala is included

Further, the functions of amygdala and hippocampal system proved to have more to do with attention and formation of specific memories than with emotions

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 cingulate bundle of fibres in the white matter) with the parahippocapal gyrus.

)

The Parahippocampal gyrus

Located in medial temporal lobe

Lies between the

hippocampal fissure and the collateral sulcus

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

)

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

)

The hippocampus

Curved elevation of gray matter

Extends throughout the entire lenghth of the floor of the inferior horn of the lateral ventricle

Expanded anterior end --- pes hippocampus Terminates posteriorly– beneath the splenium of

corpus callosum

Alveus– thin layer of white matter beneath the convex ventricular surface

Fimbria– bundle formed by nerve fibres

originated in hippocampus--- becomes continuous with the crus of fornix – passes anteriorly and inferiorly--- coloumn of fornix pass through hypothalamus into the mamillary bodies

The Subicular complex

Includes pre, para, and the subicular parts

The transition region between the hippocampus and parahippocampal gyrus

)

The amygdala

Located in medial temporal lobe

Just anterior to the hippocampal formation 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 sublenticular innominate with bed nucleus of stria terminalis(extended amygdala)

The septal area

Gray matter structure located immediately above the anterior commissure

The insula

Medial cortical gyrus located between the amygdala and the frontal lobe

)

The uncus

Formed by the amygdala and the rostral hippocampus

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, the thalamus and cortical areas

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

Histology of the limbic system 1

Cortical structure of parahippocampal gyrus is six layered. As the cortex is traced into the hippocampus,there is gradual trasnition from a six to a three layered arrangement

The hippocampus has-- outer molecular,

middle pyramidal and inner polymorphic layer. It is divided into three distinct fields– CA1, CA2 and CA3 (CA=Cornu Ammonis)

--Molecular layer-- consist of nerve fibres and scattered small neurons

--Pyramidal layer-- consist of many large pyramid shaped neurons

---Polymorphic layer-- is similar to the polymorphic layer of the cortex seen else where

Histology of limbic system 2

The dentate gyrus comprises three layers– outer acellular molecular, middle granular and inner polymorphic layer. Pyramidal layer is replaced by the granular layer

---Granular layer is composed of densely arranged rounded or oval neurons that give rise to axons that terminate upon the dendrites of the pyramidal cells in hippocampus

Basolateral nuclei of amygdala– have connectivity

and some other anatomical characteristics similar to cortical region

Histology of limbic system 3

John Allman and Giacomo Rizzolatti identified the limbic spindle cells and mirror cells the undergrid prosocial mentation

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

Histology of limbic system 4

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

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

Connections of the limbic system 1

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 stria terminalis

Connections of limbic system 2

Entorhinal cortex funnesl highly processed cortical information to the hippocampal formation and dentate gyrus

The layers of dentate gyrus connected each other and finally project to the hippocampus

The fields CA3 and CA1 of hippocampus are connected each other and finally project to subicular complex

Connections of limbic system 3

Basolateral nuclei of amygdala directly and reciprocally connected with the temporal, insular and prefrontal cortices---- n shares bidirectional connctions with the medial dorsal thalamic nuclei

Medial amygdaloid nucleus has reciprocal connections with endocrine portion of hypothalamus

Lateral part of extended amygdala connected with brainstem and lateral hypothalamus and receives cortical limbic region and the basolateral amygdaloid complex

Connections of the LS 4

The septal area reciprocally connected with the hippocampus, the amygdala, and the hypothalamus and projects to numerous structures in the brainstem

Posterior nuclei of hypothalamus shares reciprocal connections with extended amygdala

LS also interacts with components of the basal ganglial system. Thus functions of basal ganglia extens beyond the regulation of motor activities

Limbic system recieves inputs from the smell receptors in the nose

Functions of the limbic system 1

The Ls is involved in behaviour required for self-preservation and the preservation of species

control over instinctual behaviour regulated by hypothalamus and brainstem

Critical in emotions such as fear Plays a role is sexual behaviour

Has special role in memory

Functions of limbic system(ant, post cingulate) 2

Ant cingulate -- for integrating affective and motor behaviour– stimulation of the anterior cingulate triggers autonomic nervous system

Excessive stimulation leads to 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 and memory functions

Functions of limbic system(amygdala vs adrenal gland)3

Anatomy and physiology of the adrenal gland are reflected in the anatomy and physiology of the amygdala circuit and hippocampal circuit

Adrenaline secreted by the adrenal core is processed by the amygdala system

Cortisone secreted by adrenal cortex is

processed by the hippocampal formation

Functions of limbic system (functional divisions) 4

Rostral limbic system—amygdala, septum, orbitofrontal cortex, anterior insula, and anterior cingulate --important for emotions

Caudal system– hippocampus, posterior parahippocampal cortex and posterior cingulate --important for memory and visual spatial functions

The functions of limbic system(neurotransmitters) 5

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

The LS (amygdala) in emotions 1

In generel, amygdala assign emotional significance to sensory experiences

Ls directs the hypothalamus to express the motor and endocrine components of emotional states

The LS (amygdala) in emotions 2

Emotional experiences and expressions per se are accompanied and even initiated by body responses (change in heart and respiratory rate and blood pressure). The responses waned with repitition as they become familiar(habituation)

The amygdala was shown to be important to processing these experiences.(selective activation of amygdala=framing effect)

The LS(amygdala) in emotions 3

The body responses help a person to attain via the amygdala, a certain kind of memory and that emotions is due to a challenge to the pattern of that memory, not the body responses themselves

Fear is not an expression of an experience

per se, but of a memory based anticipation of pain that may be realistic and imagined

The LS (hippocampus) in memory 1

Hippocampus is concerned with recent memory converting it to long term memory– memory of the remote past events before the lesion developed is unaffected.

Anterograde amnesia is present

Hippocampal circuit places bounds, boundaries on experience and behaviour

The LS (hippocamppus) in memory 2

The hippocampus is important to an organism’s ability to reset an internal co-ordinate system. This process is critical to navigation and episodic memory

While the amygdala is processing what is novel during habituation, the hippocampus is processing the context within which habituation is happening: the hippocampus is processing what is already familiar

The co-ordinates are constructed by attending to what is not, at the moment, the focus of navigating our world. Eg: to walk through a door we must process the walls so as not to bump into them

The LS (hippocampus) in memory 3

In damage to hippocampus– the memory of what is happening to the patient personally fails to become familiar

The LS(hippocampus) in motivation and attidude 1

The hippocampal circuit brings together emotion and motivation

---The emotion—the processing of familiarty

---The Motivation– the processing of readiness to engage the world in practical manner

Attitudes (emotions plus motivation) are dispositional states that embody the experience of the individual

The LS(hippocampus) in motivation and attitude 2

Freud’s project for a scientific psychology developed a theory of motivation based on memory rather than on drive. Freud noted that motivation are the prospective aspects of memories

Papez simply stated that the circuit could account for attitudes without saying how

The LS in sexual behaviour

Directly involved in elements of sexual functioning

Stimulation of various sites of the limbic system have elicited penile erection.

Hippocampus– genital tumescence, regulation of release of gonadotropins.

Amagdala– in oral and then in genital benaviour

Olfactory sense is strongly involved in both feeding and mating

Those areas activated by emotions of fear and anxiety are notably quiescent when the woman experience an orgasm

The LS in violence behaviour

The fear is processed in amygdala – stimulation of it elicits defensive and aggressive responses

Other parts involved are– hypothalamus and septal area

The prefrontal cortex allows humans to exercise some control over their resposes

Aggressive behaviour have been noted individual with damage to the medial temporal lobe and with developing brain tumor in the limbic system

Frontal lobe injury commonest type in infancy and early childhood have lifelong consequences

Case of serial killer Arthur Shawcross

The LS in positive mental health(ant cingulate and insula) 1

Both the limbic anterior cingulate and insula appears to be active in the positive emotions of humor, trust and empathy

The prosocial biological activity of the anterior cingulate cortex and insula was highest in individiuals with highest level of social awareness--- the biological differences for positive mental health

The LS(ant cingulate gyrus) in positive mental health 2

Anterior cingulate gyrus links valence and memory to create attachment

Along with the hippocampus, the anterior cingulate is the brain region most responsible for making the past meaningful

Anterior cingulate fMRI images light up when a lover gazes at a pictures of a partner’s face or when a new mother hear her infant’s cry

The LD(insula) in positive mental health 3

Helps to bring visceral feelings into consciousness

The pain in one’s heart of grief , the warmth in one’s heart of love, and the tightness in one’s gut from fear all make their way into consciousness through the insula

The LS in positive mental health(hippocampus and amygdala) 4

fMRI studies of kundalini yoga practitioners demonstrates-- the meditation activates the activity of the hippocampus and right lateral amygdala which in turn leads to parasympathetic stimulation and sensation of deep peacefulness

The LS in positive mental health(frontal lobe) 5

Frontal lobe connectivity to the limbic system underscores its executive function which includes the ability to delay gratification, comprehend symbolic language, and most important, to establish temporal sequencing

Frontal lobes through their connection to the amygdala, hippocampus and other limbic structures encode emotional learning quite distinct from both conventional conditioning and declarative memory

The LS in schizophrenia 1

Because of its role in controlling emotions, the LS has been hypothesized to be involved in pathophysiology of schizophrenia

Limbic activation is diminished

Abnormally increased limbic activation time(threat related fascial emotions of anger and fear)

Antipsychotics block limbic receptors to dopamine as well as receptors of the extrapyramidal system

The LS in schizophrenia 2

Neuropathology findings—decrease in size of regions including the amygdala the hippocampus and parahippocmapal gyrus

Hippocampus is not only smaller, but is functionally abnormal as indicated by disturbances in glutamate transmission

Disorganisaion of neurons within the hippocampus has also been reported

The LS in BPAD

Hyperactivity and hyperfunction of some limbic and para limbic areas---including amygdala and ventrial striation as well as in the cerebellum

The LS is anxiety and OCD

In addition to receiving noradrenergic and serotonergic innervation the LS contains highest concentration of GABA A receptors

Increased activity of the septohippocampal pathway—leads to anxiety

Cingulate gyrus has been particulary implicated in pathophysiology of OCD

The LS in dementia

Involved inAlzheimers diseaseLimbic encephalitisWernick/KorsakoffAnoxic encephalopathyHSV encephalitisPost traumatic amnesiaStrokes involving PCA or thalamoperforatorsACOM aneursyms

The LS in Alzhiemers

Gross– medial temporal lobe atrophy and hippocampal atrophy most common

Plaques and tangles most frequently present in hippocampal and entorhinal cortex

Limbic encephalopathy

Usually due to metastatic ca of lung

Marked disturbance of memory for recent eventsAffective disturbance– severe anxiety and depression

Pathology– combination of degeneration and inflammation on the medial temporal lobe structures—the hippocampus, uncus, amygdaloid nucleus, dentate gyrus, insular and posterior orbital cortex

Where memory failure is predominat feature the possibity of limbic encephalopathy should be considered

The LS in Wernicke and Korsakoff

Caused by B1 deficiency

Changes involve periventricular areas: medial thalamus, hypothalamus, mamillary bodies, PAG, reticular formation

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

The LS in epilepsy n hippocampal sclerosis

Hippocampal cell loss can be considered a cause and consequence of repeated seizures

Hippocampal sclerosis—seen in 47—70% of all TLE

Limbic epilepsy

Limbic epilepsy can originate in the amygdala, hippocampus, entorhinal cortex, cingulate or orbital frontal cortex

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

Kluver Bucy syndrome

Bilateral removal of temporal lobe– amygdala, para amygdala area

Features– no evidence of fear or anger, unable to appreciate object visually, increased appetite, increased sexual activity- indscriminatly seek partnership with male, female animals

Herpes simplex encephalitis

The LS in psychosurgery

Stereotactic operations on the amygdaloid nuclei: decreased emotional excitability

OCD: cingulotomy, anterior cingulotomy, and limbic leucotomy may be effective

Pain: cingulotomy

Epilepsy:TLE

Tourette: disconnection of the anterior cingulate from the thalamus results in improvement of symptoms

References

Kaplan and saddock’s comprehensinve textbook of psychiatry 9th ed (2009), lippincott w&w

Lishman, organic psychiatry Snell’s clinical neuroanatomy for medical

students

Ganong’s review of physiology,Lange

Internet

Thank you