PRESENTER: DR. MD. OSMAN ALI The Limbic System
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