The limbic system is a set of brain structures that control emotional behaviors and motivational drives. It includes structures like the amygdala, hippocampus, hypothalamus, and others that are interconnected. The limbic system regulates survival behaviors like eating and sex. It also controls emotional states and integrates sensory information. The amygdala plays an important role in emotional behaviors and responses to stress. The hippocampus helps form long-term memories. The hypothalamus regulates many autonomic and endocrine functions as well as emotional behaviors.

1. PURNIMA KARTHA. N

2. CONTENTS
• Limbic System – Introduction.
• History
• Functions of the Limbic System
• Anatomy:
– Subcortical Structures : Amyglada, Hypothalamus, Thalamus, Septal
Region.
– Limbic Cortex: Limbic Lobe, Hippocampal Formation.
• Routes of Communication
• Related Nerve Fibres
• Reference. 2

3. LIMBIC SYSTEM
• The term limbic system has been used to
refer to the entire neuronal circuitry that
controls emotional behavior and
motivational drives.
• The limbic system includes a ring of
forebrain structures that surround the
brain stem and are interconnected by
intricate neuron pathways.
• The word “limbic” means “border.”
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4. HISTORY1937- James Papez first proposed
that specific brain circuits are
devoted to emotional experience
and expression.
1850s - Paul Broca - used the term
“limbic lobe” (part of the cerebral
cortex that forms a rim around the
corpus callosum and diencephalon)
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5. FUNCTIONS OF THE LIMBIC SYSTEM
Integration of olfactory, visceral and somatic impulses reaching
the brain
Control of activities necessary for the survival of the animal,
including procurement of food and eating behaviour.
Control of activities necessary for the survival of species-
including sexual behaviour
Establishing emotional states : pain, pleasure, docility, affection,
and anger 5

6. ANATOMY
• The anatomical structures of the limbic system consists of an
interconnected complex of basal brain elements.
6

7. PARTS OF THE LIMBIC SYSTEM
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8. SUBCORTICAL STRUCTURES
 Hypothalamus
 Hippocampus (Ammon’s horn)
along with the dentate gyrus.
 Amygdaloid nuclei
 Septal nuclei
 Paraolfatory areas
 Anterior nuclei of the thalamus.
 Portions of the basal ganglia.
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9. AMYGDALOID NUCLEAR COMPLEX
• Also called amygdaloid body or
amygdala.
• Lies in the temporal lobe of the
cerebral hemisphere, close to the
temporal pole.
• It lies deep to the uncus and is
related to the anterior end of the
inferior horn of the lateral
ventricle. 9

10. LOCATION OF AMYGDALA
• Superiorly, the complex is
related to the anterior part of the
lentiform nucleus
• Inferiorly, the complex is related
to the anterior most part of
parahippocampal gyrus
• It fuses with the anterior end of
the tail of the caudate nucleus.
• The lower end of the stria
terminalis lies in relation to the 10

11. • In the region between the amygdaloid complex and the
lentiform nucleus, there is a region of substriatal grey matter,
within which there is a collection of cholinergic neurons.
These neurons form the Basal nucleus of Meynert.
• Amyglada is also divided into 3 groups of nuclei :
11

12. • The amygdala receives afferent (input) fibers from the
olfactory bulb, orbitofrontal cortex, cingulate gyrus, basal
forebrain, medial thalamus, hypothalamus, and brainstem.
• Efferent fibres from amygdala pass through two major routes:
– Stria terminalis (which conveys fibers primarily from the
corticomedial nucleus to the septal nuclei and the
hypothalamus)
– Ventral amygdalofugal route (which also conveys input
fibers to the amygdala)
• The limbic system projections to the deep cerebral nuclei are 12

13. FUNCTIONS
• Important role in the control of emotional behaviour.
• Reciprocal projections between the amygdala & thalamus,
hypothalamus, septal nuclei, orbital frontal cortex,
cingulate gyrus, hippocampus, parahippocampal gyrus,
and brain stem modulate ANS activity and endocrine
responses.
• Coordinated responses to stress and anxiety and integrates
many behavioral reactions.
• Stimulation of the amygdala produces behavioral arousal 13

14. HYPOTHALAMUS
• The hypothalamus, which represents less than 1% brain mass, is one of the
most important of the control pathways of the limbic system.
• It has two-way communicating pathways with all levels of the limbic
system it and its closely allied structures
• Controls most vegetative and endocrine functions of the body as well as
emotional behavior.
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15. FUNCTIONS
• Cardiovascular Regulation
• Regulation of Body Temperature
• Regulation of Body Water
• Regulation of Uterine Contractility and of Milk
Ejection from the Breasts.
• Gastrointestinal and Feeding Regulation
• Hypothalamic Control of Endocrine Hormone
Secretion by the Anterior Pituitary Gland.
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16. BEHAVIOURAL FUNCTIONS
 Stimulation of lateral hypothalamus increases the general level of
activity of the animal, sometimes leading to overt rage and
fighting.
 Stimulation in the ventromedial nucleus and surrounding areas
causes opposite effects - a sense of satiety, decreased eating, and
tranquility.
 Stimulation of a thin zone of periventricular nuclei, located
immediately adjacent to the third ventricle leads to fear and
punishment reactions.
 Sexual drive can be stimulated from several areas of the 16

17. THALAMUS
The amygdala and hypothalamus project to the “limbic
nuclei” of the thalamus, which include the anterior
nuclear group and the lateral dorsal and medial
dorsal nuclei of the thalamus. These nuclei then relay
this information to the limbic lobe.
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18. SEPTAL REGION
• Masses of grey matter that lie immediately anterior to the lamina
terminalis and the anterior commissure.
• The cerebral cortex of this region shows two small vertical sulci
called the anterior and posterior para-olfactory sulci.
• The region between the anterior and posterior parolfactory sulci is
the subcallosal area (or parolfactory gyrus).
• The cortex of this region is referred to as the septal area in
distinction to the septal nuclei, which lie deep to the cortex.
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19. LIMBIC LOBE
o Bordering the limbic cortex –
Perilimbic areas.
o Limbic lobe is composed of a ring of
cerebral cortex in each side of the
brain
 orbitofrontal area
 subcallosal gyrus
 cingulate gyrus
 parahippocamal gyrus
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20. HIPPOCAMPAL FORMATION
• Hippocampal formation
includes
– hippocampus
– dentate gyrus
– gyrus fasciolaris
– indusium griseum
– medial and lateral
longitudinal striae
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21. HIPPOCAMPUS
• The hippocampus is an infolding of the cerebral cortex,
embedded within the parahippocampal gyrus of the temporal
lobe
• The hippocampus extends from the amygdala anteriorly, and
then tapers as it courses posteriorly to the inferior surface of
the splenium of the corpus callosum.
• At its anterior extent, the hippocampus displays a swelling
with several grooves resembling a paw, and is thus referred to
21

22. • Indusium griseum: thin layer of grey matter, lining the upper
surface of the corpus callosum in the hippocampal formation.
• Within the IG - embedded two bundles of longitudinally
running fibres called the medial and lateral longitudinal
striae.
• IG continuous with a thin layer of grey matter related to the
inferior aspect of the splenium of the corpus callosum: splenial
gyrus or gyrus fasciolaris
• The splenial gyrus runs forwards to become continuous with 22

23. Papez Circuit• Hippocampus receives fibres
mainly from entorhinal area,
amyglada and cingulate gyrus.
• The fornix is the main efferent
tract of the hippocampus.
• Commissure of
fornix/hippocampal commisure
Septal and anterior hypothalamic
regions Mammillary body
(which sends impulses to
cingulate gyrus through anterior
nucleus of thalamus, through 23

24. FUNCTION
• Hippocampus provides the drive that causes translation of
short-term memory into long-term memory (Long-term
potentiation).
24

25. ROUTES OF COMMUNICATION
• An important route of communication between the limbic
system and the brain stem is the medial forebrain bundle,
which extends from the septal and orbitofrontal regions of the
cerebral cortex downward through the middle of the
hypothalamus to the brain stem reticular formation. This
bundle carries fibers in both directions, forming a trunk line
communication system.
• A second route of communication is through short pathways
among the reticular formation of the brain stem, thalamus, 25

26. RELATED FIBRE BUNDLES
• Olfactory nerves, tract and
striae.
• Fornix, stria terminalis,
stria medullaris thalami,
diagonal band, and
anterior commissure.
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27. REFERENCE
• Atlas of Functional Neuroanatomy 2nd Edition -Walter J.
Hendelman
• Inderbir Singh's Textbook of Human Neuroanatomy (9th
edition) - Pritha S Bhuiyan, Lakshmi Rajgopal, K
Shyamkishore
• A Textbook of Neuroanatomy - Maria A. Patestas, Leslie P.
Gartner
• Textbook of Medical Physiology (11th edition) - Arthur C.
Guyton, John E. Hall. 27