Introduction : Emotions play very important role in our day to day life. Aid in the survival of individual. Makes person more successful in the struggle of existence. These emotions are developed in a specialised system of CNS - Limbic system.

1. Limbic system
By
Dr. Sunita M. Tiwale
Professor In Physiology
D. Y. Patil Medical College Kolhapur

2. Introduction :
•Emotions play very important role in our day to
day life.
•Aid in the survival of individual.
•Makes person more successful in the struggle of
existence.
•These emotions are developed in a specialised
system of CNS - Limbic system.

3. Definition :
•The word ‘limbic’ means a border, girdle, ring or belt.
•In 1878 Paul Broca introduced- Limbic system- a
series of structures on the inferomedial surface of the
cerebral hemisphere, which borders the junction
between the diencephalon & telencephalon.
•Limbic system-advanced part of primitive brain.
•Recently limbic system - the entire neuronal circuitry
that controls emotional behaviour & motivational drive.

4. Comparative :
•The sense of smell or olfaction is the most primitive
sensory modality.
•Highly developed in macrosmatic (keen scented
vertebrates) i.e pisces, amphibians.
•Forebrain occupied by olfactory lobes hence called
Smell brain or Rhinencephalon - helps in the detection
of food.
• In higher vertebrates due to profuse growth of
neocortex, the limbic system has been buried under the
thick neocortex.
•Neocortex has control over limbic system & olfactory
system forms a rudimentary structure.

5. • Hence man becomes microsmotic.
• Emotional behaviour in human is dependent not
much on olfaction but on other sensory modalities
like vision, hearing, taste & on the influence of
psychic cortex.
Ref : From Net

6. Physiological anatomy :
•It forms interconnecting complex of basal brain
elements.
•Localised in the middle of all these is the
extremely small 1) Hypothalamus occupying the
key position in the limbic system.
•Surrounding it are 2) Subcortical structures:
Septum pellucidum, paraolfactory area, anterior
nucleus of thalamus, portions of the basal
ganglia, the hippocampus & the amygdala.

9. Surrounding the subcortical areas-
3) limbic cortex forming a ring of cerebral cortex
beginning in the orbitofrontal cortex on the ventral
surface of the frontal lobe, extends upward into
subcallosal gyrus above the corpus callosum.
On the medial aspect of the cerebral hemisphere is
the cingulate gyrus upto parahippocampal
gyrus & uncus.

11. Histology :
Limbic system made up of allocortex (3 layers)
subdivided into -
1)Ancient cortex - Hippocampus & dentate
gyrus.
2)Old cortex - Uncus, part of para-
hippocampal gyrus (together belong to pyriform
area of olfactory cortex).
3)Mesocortex or Juxtaallocortex- Cingulate
gyrus, part of parahippocampal gyrus &
subiculum.

12. Connections of Limbic system :
Limbic system forms a link between brainstem &
neocortex. So rich connections between :
1)Limbic structures with each other.
2)Limbic structures with association cortex.
3)Limbic structures with brain stem.
1)Papez circuit :
Anterior nucleus of thalamus
↓ ↑
Cingulate gyrus Mamillary body
↓ ↑
Hippocampus → Fornix

13. Importance of Papez circuit :
1)Plays important role in short term memory (recent
memory).
2)Repeatation or rehearsal is mother of learning it is
brought by reverberation done by Papez circuit.
It converts short term memory
into long term memory (consolidation of memory).

14. 2)Median forebrain bundle: (major efferent
connection). From limbic structures to lateral & post
part of hypothalamus.
Orbitofrontal Medial nucleus
cortex of
Thalamus
Other limbic structures
↓
Lat & post part of hypothalamus
↓
Reticular formation of midbrain (desc reticular tracts)

15. Important for i)genesis of emotions.
ii)Autonomic changes associated with
emotions. Inner body functions are altered.
3)Connections of Amygdala with
Hypothalamus :
From limbic cortex, Neocortex of temporal,
parietal & occipital lobes especially auditory &
visual association areas→Amygdala.
Amygdala efferents→via stria terminalis &
ventral amygdala fugal fibres→Septal
nuclei→hypothalamus (Arcuate nuclei)

16. Hypothalamus (Arcuate nuclei) releases
Gonadotrophin releasing hormones → acts on
Anterior Pituitary which releases Luteinizing
hormones for ovulation at the time of copulation in
lower animals.
In higher animals (mammals) amygdala influences
reproductive functions but to lesser extent due to
encephalization.
1

17. 4)Connections of amygdala with smell pathway :
i)Uncus, entorhinal area (Pyriform cortex)
→Amygdala (Corticomedial nucleus in lower
animals) induces feeding & drinking behaviour.
Induces movements associated with olfaction &
eating such as licking, chewing & swallowing.
ii)Stimulation of amygdala induces certain
emotions like fear, rage, escape, punishment &
pain.

18. iii)In higher animals amygdala (basolateral nuclei)
has multiple connections hence called Window
(biological filter) where filtering of events occur.
It enables one to see his own place or status in
relation to outer environment & thought.
iv)Behavioural awareness area: It helps to pattern
the persons behavioural response so that it is
appropriate for each occasion.

19. 5)Limbic centres→Basal ganglia→ Reticular
formation.
Important in producing the external manifestations
of emotions (expression of emotions) i.e mainly
somatic responses like facial expressions & other
body gestures in response to emotions.

21. Functions of Limbic system :
1)Genesis of emotions (generating emotions).
These emotions produces different types of
behaviour (expression of emotions). Emotions has
four characteristics :
1)Cognition : Thinking process of brain which
evaluates the stimulus.
Sensory information is compared with stored
information (available by previous experience or
inheritance) e.g: Seeing an object or a person &
recognising him.

22. 2)Affect :Feeling developed in relation to that
stimulus.
3)Conation : Desire or urge to act.
4)Expression: Motor side of emotional behaviour
expressed in two ways: a)Somatic:
Emotions expressed by gestures or facial
expression (actual act performed). b)Autonomic:
Sympathetic - ↑ in HR & BP.
Parasympathetic :↓ in HR & BP.

23. Other characteristics:
1)Emotions cannot be controlled by our will i.e it
is impossible to abolish them or to prevent them
from not developing at all.
2)Emotions lasts for much longer duration even
after the stimulus is over (after discharge),this is
because of sparse neuronal connections between
neocortex & allocortex.
Nauta has stated that - Neocortex sits astride the
limbic system like a rider on a horse without reins.

24. How emotions are generated?
Sensory experience→Limbic system interpretes as
Pleasant or Unpleasant.
Neocortex translates pleasant experience as
Reward & unpleasant experience as Punishment.
Reward system or centres :
Located along the course of Medial forebrain
bundle especially in - Lateral hypothalamus on mild
stimulation, ventromedian nucleus of
hypothalamus, septum pellucidum, amygdala,
thalamus & basal ganglia extending down into
basal tegmentum.

25. Punishment centres :
Located in lateral hypothalamus on strong
stimulation, periventricular zones of hypothalamus
& thalamus, periaqueductal grey matter of
midbrain.
On stimulation leads to emotional behaviour
patterns like rage, fear, anxiety, escape
tendencies.
Degree of stimulation of these two opposing
systems affect the behaviour of individual i.e
provide background mood & motivations of the
person.

26. 2)Limbic system by means of these reward &
punishment system form the basis of learning &
memory.
Ability to learn, acquire knowledge requires limbic
system.
Major role is played by hippocampus, temporal limbic
cortex & prefrontal cortex.
Hippocampus determines whether the incoming
signals are important or not (Critical decision
making).
Selection of information is based on whether the
stimulus/sensory experience causes pleasure or pain
i.e stimulation of reward or punishment centre.

28. If reward centre is stimulated.
↓
Animal continues to do
it(repeatation). ↓
Response becomes stronger
& stronger. ↓
Leading to +ve
reinforcement.
If punishment centre is stimulated,
↓
Animal avoids to do it.
↓
Leading to -ve reinforcement.
Thus person learns the sensory experience.

29. If no reward or punishment centres are
stimulated after sensory experience then such
indifferent stimuli → no learning.
Cause is cortical responses fades away after
repeatation due to habituation.
Thus hippocampus provides the motivation or
drive to remember those experiences or thoughts
that are pleasant or unpleasant.
Thus there occurs processing in hippocampus &
this information is committed to memory by
various mechanisms-

30. 1)By reverberating neuronal circuits.
2)By presynaptic facilitation.
3)By presynaptic potentation.
Hippocampus store the new information as short
term memory.

31. Another important function of hippocampus is
consolidation of memory i.e conversion of short
term memory into long term memory.
Hippocampus transmits some type of signals that
makes the mind to rehearse the same information
again & again. This potentiates & accelerates
transfer of short term memory to long term
memory.
Cause - multiple physical & structural changes
occur in the synapse i.e DNA activation→↑
synthesis of specific proteins.

32. Mechanisms -
1)↑ in number of presynaptic transmitter vesicles,
2)↑ in number of vesicular release
sites, 3)↑ in length of
the dendrites to accommodate extra synapses.
4)Changes in the structure of the dendritic spines
for transmitting stronger signals.
Amygdala is closely associated with hippocampus ,it
encodes emotional memories.
Hence events associated with strong emotions are
remembered better.

33. 3)Preservation of self (looking after yourself)
by drives & motivation.
Drives - ability to perform.
Motivation – desire or urge to do. Basic drives
of life - hunger,thirst & defense are associated
with emotions.
Emotions for hunger, thirst are generated by
limbic system.
It also helps to execute (to carry out) this
drives & motivations to satisfy these emotions.

34. e.g - Absence of food or water creates unpleasant
feeling of deprivation.
This motivates animal to find food also helps in the
act of finding food i.e shows somatic responses.
Limbic system controls dietary patterns, nutritional
requirements of species.
Lesion in amygdala - feeding habits changed i.e
hyperphagia, herbivorous turns to carnivorous diet.
Looking after self - e.g Birds building nest.

35. 4)Preservation of species - Limbic system affects
sexual behaviour.
It is responsible for creating the sex urge(premating)
& its execution (mating) peculiar to species.
In animals sexual behaviour is regulated by neural &
endocrinal factors.
In male animals, neocortex initiates sexual behaviour.
Anterior part of hypothalamus, preoptic nucleus
stimulates sex behaviour.
Limbic areas like amygdala, frontal lobes & pyriform
cortex inhibit sexual behaviour.

36. In female animals neocortex & limbic cortex ↑
sexual activity during heat or estrus cycle
Ovulation occurs during estrus cycle.
Anterior hypothalamus, preoptic nucleus ↑ sexual
behaviour.
Pheromeres produced in vaginal secretion act via
olfactory (vomeronasal organ) thus regulates
sexual behaviour.
ii)Looking after young ones (rearing of young) i.e
maternal & paternal behaviour is controlled by
limbic cortex is based on stimulation of reward
centre.

37. 5)Instincts & instinctional behaviour is inborn
ability, passed on generation to generation it has
genetic base.
Natural tendency to behave in a certain way
without reasoning or training (innate impulse or
intuition). e.g - Birds learn to fly by instinct. Birds
migrate to lake, ponds where they are born.
Instinctive behaviour patterns are specific to a
species.
Migration of Artic Turks from north pole to South
pole.

38. 6) Visual comprehension & recognition part of limbic
system.
7) Biological rhythms:
Life cycle :Infancy → childhood → Puberty → adult
(stage of maintainence) → old age & senility.
Circadium rhythm : Day & night rhythm, wake &
awake state governed by limbic system.
8)Primitive function of limbic system is perception of
sense of olfaction or smell.

39. i) Very very old olfactory system: Concerned with
basic olfactory reflexes. e.g smell of food or
emotional drives → primitive responses like licking of
lips, salivation & ↑ GIT motility.
ii) Less old olfactory system: Hippocampus learn to
like or dislike (aversion) for certain foods.
iii)Newer olfactory system: Analysis of odour.

40. Applied aspect:
1)Psychosomatic illnesses,
2)Anterograde amnesia,
3)Alzemier’s disease,
4)Korsakoff’s psychosis, &
5)Kluver Bucy Syndrome.
1)Psychosomatic illness : Needs, aspirations &
social organisation, expectations of civilized
behaviour has made man a miserable creature than
other species.
So he is unable to express his emotions. He has to
supress himself from doing physical & verbal
violence.

41. But autonomic & endocrine manifestations do
occur.
As a result of this dissociation, the negative
emotion lasts longer & its ANS manifestations
prolonged.
Such episodes if frequent became permanent.
Diseases like hypertension & diabetes have
strong psychosomatic basis.

42. 2) Korsakoff’s Psychosis : Nutritional
deficiences associated with alcoholism.
Lesion in mammillary bodies or Papez’s circuit.
Manifestations: Confusion, confabulation (honest
lying - memory disturbance in which a person
confuses imagined scenarios with actual
memories with no intent to deceive) & recent
memory deficit so learning is defective.

43. Anterograde amnesia:
Lesion at hippocampus.
Person unable to store verbal & symbolic types of
memories (declarative type of memory) in long
term or intermediate memory.
So no new long term memories can be formed
which are basis of intelligence.
Retrograde amnesia: Inability to recall past
memories –lesion in thalamus(search the memory
store houses & read or find out memories).

44. Alzheimers disease: Premature aging of brain.
Begins in mid adult life, progresses rapidly -
extreme loss of mental powers as seen in very
old age.
Features : Memory impairment (due to loss of
neurons in that part of limbic pathway that drives
the memory process.
Deterioration of language, visuo spatial deficit,
motor & sensory abnormalities.
Later behavioural disturbances.

45. Cause : Increased amount/accumulation of
Beta-Amyloid peptide in the form of amyloid
plaques in wide spread areas of brain.
Abnormality of gene that controls apolipoprotein
E (a blood protein that transports cholesterol to
tissues).
Formation of anti amyloid antibodies.
Hypertension, diabetes & hyperlipedemia ↑ the
risk for developing this disease.

46. Conclusion :There is impact of superimposition of
the massive neocortex on the limbic system in a
highly evolved animal like man - ego.
Structure & function of the limbic system is well
integrated with neocortex. So cannot separate any
intellectual work from its emotional counterparts.
To the basic urges of hunger, thirst & sex,
neocortex has added the urge - to know, to excel
(be exceptionally good or surpass others -
superego) & to be right & fair.

47. Once basic urges are satisfied, the human
organism still remains dissatisfied & craves for
more higher needs.
Overall impact of neocortical activity & resulting
civilization has been to suppress & conceal basic
urges & well as emotions.
Emotions have become repugnant (disgusting or
unacceptable) to most highly evolved animal.

48. Finally man has realized that because of the
uncertainties in the world & the complexities of his
needs, he will never be happy if he insists on
satisfying all his desires.
Therefore he has found different ways of
changing his attitude to events so that he can be
happy in spite of all desires not satisfied.
This attitude is called contentment or reduction of
desires.
In physiological terms, man turns to the neocortex
to satisfy the limbic need for happiness.

49. Kluver Bucy Syndrome: Infection in middle ear→
breaks into cranial cavity→ Damage to or removal of
temporal lobe, loss of amygdaloid nucleus &
hippocampus.
Features : 1) Hypermetamorphia: Animal extremely
restless,will not sit quietly, constantly moving
around.
In human, person will move around, examining all
objects again & again.
2)Oral tendencies: Any object seen is taken & put
into mouth. Animal then spits it out, repeats again.
3)Tameness & loss of all fear. e.g: monkey holds
snake & handles it. In normal animal, site of snake
causes alarm & avoids it.

51. 4)Visual agnosia: Loss of ability to recognize the
object by vision.
5)Loss of ability to learn new things, loss of Papez
circuit.
6)Change in dietary habits, vegetarian becomes
nonvegetarian animal eats anything that comes in
its way even if it is dirty can eat own faecal matter.
7)Hypersexuality so intense it does not distinguish
between different species.
Instinctival behaviour completely changed.

53. References :
Understanding Medical Physiology
-By RL Bijlani
-Text book of Medical Physiology
-By Guyton & Hall
-Text book of Medical Physiology
-By A.K.Jain
-Review of Medical Physiology
-By Ganong
-Net Source (Pic & etc.)

54. Thank you