The limbic system is a set of brain structures involved in emotion, behavior, motivation, and memory. It includes the hippocampus, amygdala, septum, cingulate gyrus, and parts of the hypothalamus and thalamus. The limbic system regulates functions like aggression, fear response, appetite, sleep, dreams, social cognition, and memory formation and storage. Damage to limbic structures can impact conditions like temporal lobe epilepsy, limbic encephalitis, and Alzheimer's disease.

1. T h e L imb i c
S y s t em
Presenter: Dr. M. Hemalatha
Moderater: Dr.V. Sharbandhraj

2. Over view of presentation
• History
• Anatomy
• Histology
• Functional circuitry
• Functions of the limbic system
• Clinical implications

3. 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

4. Components of limbic system

5. Components of limbic system
1. Limbic lobe
a) cingulate gyrus
b) parahippocampal gyurs
2. Hippocampal formation
a) 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.

6. 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 fibres
in the white matter-cingulum)
with the parahippocapal gyrus.

7. 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
• Cortical structure of
parahippocampal gyrus is six
layered.

8. 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.

9. 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=Cornu
ammonis)
Alveus– thin layer of white matter
adjacent to the poly morphic layr of
hippocampus

10. • 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

11. 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)

12. 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
Uncus
Formed by the amygdala and the
rostral hippocampus

13. 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

14. 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

15. 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 than
in primates-reside in insula, ant cingualte
- mediate empathy– the experience of
feeling the emotions of another

16. 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 stria
terminalis
Neurotransmitter system in limbic system include– dopamine,
serotonin, noradrenergic, and cholinergic systems

17. PAPEZ CIRCUIT
PAPEZ CIRCUIT

18. Hippocampus conections
major inputs---layers 2 &3 of ERC
septal & hypothalamic fibers
via fornix
few from c/L hippo campal formation
glutaminergic fibers frm –
fimbria

19. Hippocapal efferents

20. Circuits of amygdala

23. 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

24. Olfaction:
Amygdala and ERC are closely related olfactory cortex-role
in processing of olfactory sensations.
Amygdala-involves in emotional response to smell
ERC- concerns with olfactory memories

25. Appetite and eating behaviors:
Amygdala –food choice and emotional modulation of
food intake
Hypothalamus:LN-centre for control of feeding
VMN-functions satiety centre
EMOTIONAL RESPONSES
FEAR: -
response- produced by stimulation- amygdala and
hypothalamus
- amygdala involves in fear learning
- imaging studies -viewing fearful faces stimulates leftamygdala
damage-abolishes fear

26. Autonomic endocrine responses
stimulation of the anterior cingulate &
hypothalamus triggers -ANS
Excessive 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

27. 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

28. 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.

29. 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

30. Sexual behavior

31. 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 copulatory
ability,^ glutamate –MPOA- facilitate copulation and
genital reflexes during ejaculation

32. 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,mammilary
body,DM neucleus of thalamus-storage of recent memory
--dysfunction of circuit-korsakoffs syndrome

33. Addiction and motivation
• Reward circuitry under lying addictive behavior includes
amygdala and nucleus accumbens
• Amygdala plays acentral role in cue induced relapse.relapse
is 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,nucleus
accumbense involved in motivation to take drugs of abuse
and compulsive nature of drug taking.

34. CLINICAL IMPLICATIONS
• TEMPORAL LOBE EPILEPSY—mc-hippocampal sclerosis
hippocampal sclerosis+amygdala+parahppocampal gyrus
termed –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,invluntory
movements and ataxia

35. Alzhiemers dementia
• Gross– medial temporal lobe atrophy and hippocampal
atrophy most common
• Plaques and tangles most frequently present in hippocampal
and entorhinal cortex
• Hippocampal damage-antegrade amnesia
Hypofunction and hyperfunction of some anterior limbic
areas---prefrontal regions and sub cortical structures-thalamus,
striatum,amygdala
BPAD

36. Korsakoffs psycosis
• Caused by B1 deficiency-damage periventricular areas:
medial thalamus, hypothalamus, mamillary bodies,reticular
formation
• 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.

37. • Anxiety disorders-may be result -failure of
ant cingulate, hippocampus to modulate
amygdala
Kluver-bucy syndrome
• 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

38. 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 mesolimbic
system to the ventral striatal system, resulting in
positive symptoms

39. Autism and aspergers syndrome-cingulategyrus,
and affective processing-dysfunction leads -ASD
ADHD
amygdala (BLcircuit) mediates cognitive
• 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

40. References
• Kaplan and saddock’s comprehensinve textbook
of psychiatry
• Lishman, organic psychiatry
• Adams & victor neuroanatomy
• Lymbic system by E. Mohan das
• Internet