The limbic system consists of cortical and subcortical brain structures involved in emotion, behavior, motivation, and memory. It includes the limbic lobe, hippocampal formation, amygdala, hypothalamus, and connections between them. The hippocampal formation plays a key role in memory through the Papez circuit, connecting to the mammillary bodies, anterior thalamus, and cingulate gyrus. The amygdala is important for emotional processing and attaching emotional significance to stimuli. The hypothalamus regulates autonomic functions and behaviors like feeding, addiction, and sexual behavior through connections with other limbic structures and the brainstem.

1. Limbic System

2. INTRODUCTION
The term Limbic comes from the latin word “LIMBUS” means “RING”.
Limbic system consists of several cortical and subcortical structures, which
form a ring-like structure around the upper end of brainstem.
The term limbic system has been applied in the past to certain regions of the
brain that are believed to play an important role in the control of visceral
activity.
The olfactory system in man is not only concerned with smell but also
activates other neural systems for emotional behaviour and hence included
as a part of limbic system.
The limbic system plays a vital role in elaborating of emotional behavior,
drive, and memory.

3. Components of the Limbic System
A. Regions of grey matter in limbic system
B. Regions of white matter in limbic system

4. A.Regions of grey matter in limbic system
The limbic system of region of gray matter consists of
The cortical regions include ;
• limbic lobe
• hippocampal formation
• septal area
• olfactory areas.
 The subcortical structures include;
• amygdaloid nuclear comple
• hypothalamus
• anterior nucleus of thalamus
• habenular nucleus
• reticular formation

5. LIMBIC LOBE CONT..
The cingulate gyrus (Latin = Belt ridge) dorsal to the corpus callosum is heavily
interconnected with the association areas of the cerebral cortex.
o Autonomic functions regulating heart rate and blood pressure as well as
cognitive, attentional and emotional processing.
The parahippocampal gyrus in the medial temporal lobe contains several distinct
regions, the most important being the entorhinal cortex (ERC).
The ERC funnels highly processed cortical information to the hippocampal
formation and serves as its major output pathway.
oIt is primary involved in memory processing

6. 1.LIMBIC LOBE
The limbic lobe situated at the inferomedial aspect of the cerebral
hemispheres, consists of two concentric gyri surrounding the corpus
callosum.
Broca proposed that the larger outer gyrus be named “limbic gyrus” and the
smaller inner one “the intralimbic gyrus”.
The limbic gyrus (limbic lobe) consists of the isthmus of the cingulate gyrus,
the parahippocampal gyrus (both of which are continuous via a bundle of
white matter called “cingulum”) and the subcallosal area.

7. Sagittal section of the brain showing the
location of the limbic lobe

8. 2.SEPTAL REGION
These are certain masses of grey matter that lie immediately anterior to
the lamina terminalis and the anterior commissure
 They include the paraterminal gyrus, prehippocampal rudiment and
subcallosal area (or parolfactory gyrus).
Phylogenetically, the septal region is divided into a precommissural
septum and a supracommissural septum
The septal area is the precommissural septum.The supracommissural
septum is represented by the septum pellucidum.
The septal area is continuous inferiorly with the medial olfactory stria.
Superiorly, it is continuous with the indusium griseum

9. Hippocampal formation and septal areas

10. Connections
Afferent
Septal area predominantly receives afferents from:
• Olfactory tract through medial olfactory stria
• Amygdala through stria terminalis
• Hippocampus through fornix
Efferent corrections from septal nuclei are predominantly
to habenular nuclei through stria medullaris thalami (stria habenularis)

11. 3.HIPPOCAMPAL FORMATION
In the human embryo, the hippocampal formation is C-shaped. The upper
part of the formation remains underdeveloped and lines the upper surface
of the corpus callosum as indusium griseum.
Major structures of the hippocampal formation
 Dentate gyrus
• The medial margin of dentate gyrus is free and bears a series of notches
that give it a teeth-like (dentate) appearance; hence, the name dentate
gyrus
• contains granule cells that receive hippocampal input and project it to
the pyramidal cells of the hippocampus and subiculum.

12. HIPPOCAMPAL CONT...
 Hippocampus (cornu ammonis)
 is made up of three layers only . These are as follows:Superficial
molecular layer,Middle pyramidal cell layer,Deep polymorphic cell layer
 contains pyramidal cells that project via the fornix to the septal area and
the hypothalamus.
Subiculum
• receives input via the hippocampal pyramidal cells.
• projects via the fornix to the mamillary nuclei and the anterior nucleus
of the thalamus.

13. Coronal section of the hippocampus

14. Connections of the Hippocampus
Afferent
Hippocampus receives fibres mainly from entorhinal area (area 28), olfactory
cortex, amygdala, opposite hippocampus, parahippocampal gyrus.
Efferent
The fornix is the main efferent tract of the hippocampus.The fibres leaving the
hippocampus pass:
• To the opposite hippocampus through the commissure of fornix/hippocampal
commissure
• To the septal and anterior hypothalamic regions
• To the mamillary body, which sends impulses to cingulate gyrus through
anterior nucleus of thalamus, through Papez circuit

15. Papez Circuit (Hippocampal Circuit)
It is a circular pathway that interconnects certain important structures in
limbic system. It is concerned with short-term memory.
Papez in 1937 described the circuit, beginning from the hippocampus
projecting via the fornix to mamillary nucleus,
 the mamillary nucleus projecting via the mamillothalamic tract to the
anterior nucleus of thalamus,
anterior nucleus of thalamus projecting to the cingulate gyrus, and the
cingulate gyrus projecting via the cingulum back to the parahippocampal
gyrus and hippocampus.

16. Scheme to show Papez circuit

17. 4. Amygdaloid nuclear complex (amygdala or
amygdaloid body )
•The complex lies in the temporal lobe of the cerebral hemisphere,
close to the temporal pole.
•It is a basal ganglion underlying the parahippocampal uncus.
•It produces activities associated with feeding and nutrition when
stimulated.
•It may cause rage and aggressive behavior when stimulated.
•It is divided into a corticomedial group and a basolateral group. The
corticomedial group receives olfactory input this makes amygdaloid
body to play an important role in smell-mediated sexual behaviour, and
the basolateral receives prodigious cortical input.

18. Connections of amygdala
Afferent
The amygdaloid nuclear complex receives afferents mainly from
primary olfactory cortex, hippocampus, hypothalamus, thalamus
(medial dorsal nucleus), ventral striatum, ventral pallidum, cerebral
cortex and brainstem reticular formation.
Efferent
Efferent fibres from amygdala pass through two major routes:
• Stria terminalis—to septal nuclei, olfactory areas
• Ventral amygdalofugal route

19. Structure and location of amygdaloid nuclear
complex

20. 5.Hypothalamus
It is a major part of the limbic system that projects to the brainstem and spinal
cord.It is a division of the diencephalon.
It consists of bunch of nuclei but the main that are most important when it
comes to the limbic system are mammillary nuclei contained in mammillary
bodies and autonomic nervous nuclei
 Mamillary nuclei
receive input from the hippocampal formation (specifically the subiculum) via
the fornix. It receive input from the dorsal and ventral tegmental nuclei and the
raphe nuclei via the mamillary peduncle.
• project to the anterior nucleus of the thalamus via the mamillothalamic tract.
• contain hemorrhagic lesions in Wernicke encephalopathy

21. Connections of hypothalamus
 Afferent connections to the hypothalamus
• derive from the following structures: Septal area and nuclei and
orbitofrontal cortex, Hippocampal formation, Amygdaloid complex, Primary
olfactory cortex (area 34), Mediodorsal nucleus of the thalamus, Brainstem
nuclei
Efferent connections
• project to the following structures: Septal area and nuclei, Anterior
nucleus of the thalamus,Mediodorsal nucleus ofthethalamus,Amygdaloid
complex,Brainstem nuclei and spinal cord.

22. 6.Thalamus
It consists of two main parts involved in limbic system
 Anterior nucleus of the thalamus
It receives input from the mamillary nucleus via the mamillothalamic
tract and fornix and projects to the cingulate gyrus.It is a major link in
the limbic circuit of Papez.
 Mediodorsal nucleus of the thalamus
It has reciprocal connections with the orbitofrontal and prefrontal
cortices and the hypothalamus.It receives input from the amygdaloid
nucleus.It plays a role in affective behavior and memory.

23. B.Regions of white matter in limbic system
 Function to connect other limbic nuclei with one another.It include major
limbic fiber system which are explained below
1.Fornix
 The ventricular surface of the hippocampus is covered by a layer of nerve fibres
that constitute the alveus. The fibres of the alveus pass medially and collect to
form fimbria.
 The fimbria runs backwards along the medial side of the hippocampus to
become continuous with the fornix
 Projects from the hippocampal formation to the hypothalamus (mamillary
nucleus), the anterior nucleus of the thalamus, and the septal area.Projects
from the septal area to the hippocampal formation.

24. 2.Stria terminalis
 This bundle of fibres begins in the amygdaloid complex and runs
backwards medial to the caudate nucleus. The stria terminalis connects
amygdaloid nucleus to: Septal area,Hypothalamus,Habenular nuclei,
through the stria medullaris.
3. Ventral amygdalofugal pathway
 projects from the amygdala to the hypothalamus, thalamus, brainstem,
and spinal cord.
4.Mammillothalamic tract (also called bundle of Vicq d'Azyr)
 Itis the bundle of fibres, which carries impulses from mamillary
body(hypothalamus) to the anterior nucleus of thalamus.

25. 6.Mamillotegmental tract
 conducts fibers from the mamillary nuclei(hypothalamus) to the
dorsal and ventral tegmental nuclei(doperminergic area of the mid
brain).
5. Medial forebrain bundle
 It interconnects the septal area and nuclei, the hypothalamus, and
the midbrain tegmentum
 It interconnects pre-frontal cortex and lateral hypothalamusand
reticular formation of brainstem

26. FUNCTIONS OF LIMBIC SYSTEM
Limbic system is involved in the following functions
A. Olfaction
B. Memory
C. Behavioural responses
D. Emotional responses

27. A. OLFACTION
Olfaction process is initiated by odorants
activating olfactory receptor neurons in
olfactory mucosa of the nose
Axons leave olfactory mucosa in the olfactory
nerves to olfacory bulb through cribriform plate
These axons synapses with cells of the
olfactory bulb to give rise to axons that enter
olfactory tract
Olfactory tract neurons then project to primary
olfactory cortex through lateral olfactory stria
 Collaterals in the olfactory tract synapse also
with the anterior olfactory nucleus which in turn
feed back both the ipsilateral and contralateral
olfactory bulbs through the medial olfactory
stria and anterior commissure

28. Primary cortex
Consists of
 Piriform cortex
 Periamygdaloid cortex
Primary olfactory cortex receives axons direct from olfactory tract through lateral olfactory
stria
Some fibres of the olfactory tract also project to corticomedial nucleus of the amygdala
 These projections may be important in emotional and motivational aspects of olfaction due to
the fact that Amygdala is concerned with emotion and drive
The primary olfactory cortex projects to several secondary olfactory areas
 The piriform cortex projects to the anterior entorhinal cortex
 Since the entorhinal cortex is involved in memory; then this projection may explain the
occasional ability of odors to evoke vivid memories
 The piriform cortex also projects to orbitofrontal olfactory area, basolateral amygdala, lateral preoptic area

29. B. MEMORY
One of the most fascinating and important functions of the brain is its remarkable
ability to form memories
There is a particular circuit that is part of limbic system which is important in
memory and learning and this is called papez circuit
Working function of papez circuit
It begins from the hippocampus projecting via the fornix to mamillary
nucleus,
 the mamillary nucleus projecting via the mamillothalamic tract to the
anterior nucleus of thalamus,
anterior nucleus of thalamus projecting to the cingulate gyrus, and the
cingulate gyrus projecting via the cingulum back to the parahippocampal
gyrus and hippocampus for storage

30. MEMORY cont….
But also cingulate gyrus projects to the pre-frontal cortex(found in
frontal lobe) which is involved in thought processes,decision
making,reasoning and judgement
This communication between cingulate gyrus and pre-frontal cortex
enables memory to be involved in our thought process and in our
decision making

31. C. EMOTION
Emotions & Drive appear to be mediated by complex interactions among
numerous brain regions including
Amygdala, Limbic cortex, Septal area, Ventral striatum, association cortex,
hypothalamus, brainstem autonomic and arousal pathways
The Amygdala plays a central role in emotion and drive, but the other
components are essential as well
Amygdala is important for attaching emotional significance to various stimuli
perceived by the association cortex
In other words, Amygdala is important in states of fear, anxiety and agression
When the both amygdala are have been ablated, behaviour tends to be placid
Not easily excited or upset!

32. EMOTION CONT….
Reciprocal connections between
the amygdala and hypothalamic
and brain centres for autonomic
control mediate changes in heart
rate, peristalsis, gastric
secretions, sweating etc
commonly seen with strong
emotions

33. 4.BEHAVIOURS
There are three types of behaviours that limbic system is concerned
with which are
a.feeding behaviours
b.sexual behaviours
c.motivational behaviours

34. BEHAVIOURS CONT…
a.feeding behaviours
Amygdala plays a role in food choice and emotional modulation of food intake.
 The lateral nucleus of the hypothalamus is the center for control of feeding whereas the
ventromedial nucleus functions as the satiety center.
b.addiction and motivational behaviours
The reward circuitry underlying addictive behavior includes amygdala and nucleus
accumbens.
The amygdala plays a central role in cueinduced relapse. Relapse associated with cues,
stress and a single dose of a drug of abuse (Comment: which one? What kind?) results in
release of excitatory neurotransmitters in brain areas like hippocampus and amygdala.
The pathway of motivated behavior involves the prefrontal cortex, the ventral tegmental
area (VTA), the amygdala especially the basolateral amygdala and extended amygdala, the
nucleus accumbens core and the ventral pallidum.
 This pathway is involved in the motivation to take drugs of abuse (drug-seeking) and the
compulsive nature of drugtaking.

35. BEHAVIOURS CONT…
c.sexual behaviours
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).
 MeA sends direct and indirect innervations (through the bed nucleus of
the stria terminalis) to the medial preoptic area (MPOA). MPOA and MeA
receive genitosensory input from the spinal cord through the central
tegmental field (CTF).
 The parvocellular portion of the CTF called the subparafascicular nucleus
(SPFp) seems to be especially important for stimuli related to ejaculation.
The MPOA sends efferents to the paraventricular nucleus of the
hypothalamus (PVN), the ventral tegmental area, the nucleus
paragigantocellularis and other autonomic and somatomotor areas

36. BEHAVIOUR CONT..
The parvocellular part of the paraventricular nucleus (PVN) of the hypothalamus
contains neurons that send direct oxytocinergic and vasopressinergic projections
to the lumbosacral cord.
 Dopamine can trigger penile erection by acting on oxytocinergic neurons located
in the paraventricular nucleus of the hypothalamus.
 Activation of oxytocinergic neurons originating in the PVN and projecting to
extrahypothalamic brain areas, by dopamine and its agonists—excitatory amino
acids (Nmethyl-D-aspartic acid) or oxytocin itself or by electrical stimulation leads
to penile erection. The inhibition of these neurons on the other

37. APLLIED ANATOMY
1. Klüver-Bucy syndrome
 Kluver-Bucy syndrome results due to a bilateral destruction of the amygdaloid body and
inferior temporal cortex.
 It is characterized by visual agnosia, placidity,hypermetamorphosis, hyperorality and
hypersexuality.
 This disorder may be caused by many conditions including cerebral trauma; infections
including herpes and other encephalitides; Alzheimer's disease and other dementias;
Niemann-Pick disease and cerebrovascular disease.[14]
2. Korsakoff syndrome (amnestic–confabulatory syndrome).
Korsakoff's psychosis is caused by damage to mammillary bodies, dorsomedial nucleus of
thalamus and hypothalamus (diencephalic memory circuit).
It is a syndrome associated with chronic prominent impairment of recent and remote
memory. Recent memory is characteristically more disturbed than remote memory.

38. APPLIED ANATOMY CONT..
3. Epilepsy
 Temporal lobe epilepsy is the most common epilepsy in adults and is most often
caused by hippocampal sclerosis.
 Hippocampal sclerosis with additional involvement of the amygdala and
parahippocampal gyrus is termed mesial temporal sclerosis (MTS)
4. Limbic encephalitis
Limbic encephalitis is a paraneoplastic syndrome that has been reported with
carcinoma of the lung, breast and some other primaries.
The mechanism of disease is not known but it manifests as encephalitis that primarily
involves the hippocampus, amygdala, cingulate gyrus, insula and orbital-frontal cortex.
Afflicted patients develop subacute onset of memory loss, dementia, involuntary
movements and ataxia.

39. APPLIED ANATOMY CONT..
5.Dementia
Degenerative changes in the limbic system likely have a role in the genesis
of neurodegenerative diseases, particularly Pick's disease and Alzheimer's
disease.
 Marked atrophy is found in the limbic system, most notably the dentate
gyrus and hippocampus.
6.Anxiety disorders
Anxiety disorders may be the result of a failure of the anterior cingulate
and hippocampus to modulate the activity of the amygdala (top-down
regulation).

40. APPLIED ANATOMY CONT..
7.Autism
Autism and Asperger's syndrome involve the disproportionate impairment in
specific aspects of social cognition.
Limbic structures involved include the cingulate gyrus and amygdala, which
mediate cognitive and affective processing.
The basolateral circuit integral for social cognition is disrupted in autism
spectrum disorders.
8.Schizophrenia
 The Papez circuit is probably involved in schizophrenia. The evidence for this is
the distortion of cortical neuronal organization of layer II of the ERC(Entorhinal
cortex), decreased size of hippocampus and the reduced number of GABAergic
cells in the cingulate and anterior thalamus with resultant glutamatergic
excitotoxicity. The other circuit involved is the basolateral circuit which mediates
the social cognition deficits in schizophrenia.[