The limbic system is a ring of structures located deep within the brain that are involved in emotion, motivation, learning, and memory. It includes structures like the hippocampus, amygdala, hypothalamus, and cingulate gyrus. The limbic system regulates emotional responses, controls certain autonomic functions like breathing and heart rate, influences reward and punishment behaviors, and plays a role in forming memories and social cognition. Dysfunctions of the limbic system are implicated in various neurological and psychiatric conditions like epilepsy, dementia, anxiety disorders, and schizophrenia.

1. LIMBIC SYSTEM
DR. YASHASREE POUDWAL
K.J.SOMAIYA HOSPITAL

2. INTRODUCTION
 Limbic- border
 Refers to a ring of grey matter on the medial aspect of
the cerebral hemispheres
 Entire neuronal circuitry that controls emotional
behavior and motivational drive
 Network of structures associated with emotions, basic
survival and sociosexual behavioral patterns,
motivation and learning

4. HISTORY
 Paul Pierre Broca in 1878 described The Great Limbic
lobe or ‘le grand lobe limbique’
 In 1937 James Papez wrote a paper called ‘proposed
mechanism of emotion’ which elaborated the putative
role in emotion.
 In 1952 Paul Mclean coined the term “limbic system’.
Also proposed the ‘Triune brain theory’

5. PAUL
BROCA

6. COMPONENTS
 Limbic lobe
 Cingulate gyrus
 Parahippocampal gyrus
 Hippocampal formation
 Dentate gyrus
 Hippocampus
 Subicular complex
 Amygdala
 Septal area
 Hypothalmus
 Mamillary body
 Ant. Nucleus of thalamus

8. LIMBIC LOBE
 Situated on inferomedial aspect of cerebral
hemispheres
 2 concentric gyri surrounding the corpus callosum
 Outer larger gyrus ‘limbic gyrus- consists of isthmus of
cingulate gyrus, parahippocampal gyrus (continuous-cingulum)
and subcallosal area.
 Inner smaller ‘intralimbic gyrus’
 Enthorhinal complex(ERC) which funnels highly
processed cortical information to hippocampal
formation. Major output pathway

9.  Cerebral association area for control of
behavior
 Two way communication and association
linkage between the neocortex and lower
limbic structures
 Essentially all behavioural patterns can be
elicited by specific portions of the limbic cortex
 Ablation of some limbic cortical areas can
cause persistent changes in an animal’s
behavior

10. HIPPOCAMPAL FORMATION
 Hippocampus and its adjacent temporal and parietal
lobe structures, all together called the hippocampal
formation
 Has numerous but mainly indirect connections with
many portions of the cerebral cortex, amygdala,
hypothalamus, septum and the mammillary bodies
 Hyper-excitable- prolonged discharges with slight
stimulus
 Involved with sensations
 Associated with long term memory

12. DENTATE GYRUS
 3 layered- outer acellular molecular, granular middle
and inner polymorphic layer
 Thought to contribute to formation of new episodic
memories, spontaneous exploration of novel
environments.
 One of few sites in brain known to have high rates of
neurogenesis.

13. HIPPOCAMPUS
 Sea horse in Greek
 Trilaminate
 On basis of different cytoarchitecture and connectivity
has 4 fields: CA1,CA2, CA3, CA4
 The thin layer of fibers adjacent to the polymorphic
layer of the hippocampus is known as the alveus.
These fibers coalesce to form the fimbria.

16. SUBICULAR COMPLEX
 Most inferior component
 Lies between the entorhinal cortex and CA1 subfield
of the hippocampus
 Believed to play a role in human epilepsy
 Also implicated in working memory and drug addiction
 Suggested that dorsal subiculum is involved in spatial
relations and ventral cubiculum regulates the HPA axis

17. AMYGDALA
 Almond shaped structure deep within temporal lobe
 Lies at the ant. End of the hippocampal formation and
ant. Tip of inferior horn of the lateral ventricle
 Structurally diverse. Consists of 13 nuclei
 Window of the limbic system: wide aff and eff
connections with visual and auditory association areas

22. FUNCTIONS OF AMYGDALA
 Behavioral awareness area
 Project into the limbic system one's current status in
relation to both surroundings and thoughts
 Make the person’s behavioral response appropriate
for each occasion
 Relate environmental stimuli to coordinated behavioral
autonomic and endocrine responses in species
preservation-

24. REGIONS OF THE AMYGDALA
 Large basolateral region: provides direct input to basal
ganglia and motor system
 Small corticomedial group of nuclei: related to
olfactory cortex especially in lower animals
 Medial and central nuclei: connected to hypothalamus
 Other amygdaloidal nuclei
 Extended amygdala ( centromedial amygdala,
sublenticular sustantia innominata and bed nucleus of
stria terminalis

25. SEPTAL AREA
 Grey matter structure immediately above the anterior
commissure
 Extensive reciprocal connections with the
hippocampus via fornix

26. HYPOTHALAMUS
 Lies at the center of the limbic system
 Confluence of many neural pathways
 Subdivided from ant to post into 3 zones- supraoptic,
tuberal region and the mammillary region.
 governs the involuntary internal responses of various
body systems in preparation for appropriate action to
accompany a particular emotional state.

27. MAMILLARY BODIES
 act as a relay for impulses coming from
the amygdalae and hippocampi via the mamillo-thalamic
tract to the thalamus
 This circuit, from amygdalae to mammillary bodies,
and then on to the thalamus, is part of the larger
'Papez circuit'.
 They, along with the anterior and dorsomedial nuclei
in the thalamus, are involved with the processing
of memory
 They are believed to add the element of smell to
memories.

30. ANTERIOR THALAMIC
NUCLEUS
 Collection of nuclei at rostral end of the dorsal
thalamus
 Receive afferents from mammillary bodies and
subiculum
 Project to the cingulate gyrus
 Play a role in modulation of alertness, learning and
memory

31. FUNCTIONAL CIRCUITARY

32. PAPEZ CIRCUIT
 James Papez’s delineation of a circuit unraveled the
basis of cortical control of emotion.
 Recent studies show that it has a more significant role
in memory functions than in emotions
 Papez circuit was later modified by American
neuroscientist and physician Paul D. MacLean
 The Papez circuit involves various structures of the
brain. It begins and ends with the hippocampus

33.  linked the hippocampus with the cingulate cortex, via
the mammillary bodies and anterior thalamus.
 He proposed that emotional expression is organized
in the hippocampus, experienced in the cingulate
gyrus and expressed via the mammillary bodies.
 The hypothalamus was considered to be the site
where hippocampal processes gain access to the
autonomic outflow that controls the peripheral
expression of emotional states.
 The Papez circuit is now widely accepted to be
involved with cognitive processes.

34. PAPEZ CIRCUIT

35. HIPPOCAMPAL AFFERENTS
 Major input into the hippocampal formation arises from
neurons in layers II and III of the entorhinal cortex.
 In addition, some septal and hypothalamic formation
reach the hippocampal formation via the fornix
 Few fibers also arrive from contralateral hippocampal
formation via the hippocampal commissure

36. Connection
s of
hippocamp
al formation

37. INTERNAL CIRCUITS
 Intrinsic connections of the hippocampus involve
fibers from the entorhinal area, dentate gyrus,
ammon’s horn and subiculum.
 The three primary pathways of this area are called the
perforant pathway, mossyfibers and Schaffer
collaterals.
 Existence of a fourth pathway, the alvear pathway, has
been questioned, from the entorhinal area to ammon’s
horn

38.  Perforant path where glutamateric fibers from the
entorhinal area perforate the subiculum and reach the
dentate gyrus.
 The glutamatergic mossy fibers then extend from the
dentate gyrus to CA3 (pyramidal layer)
 Many axons of CA3, however, give off the Schaffer
collaterals that reach the dendrites of CA1.
 CA1 is considered the main output of the
hippocampus with fibers extending to the alveus,
fimbria and then fornix.
 A supplementary linkage with the subiculum also is
believed to be present

39. INTERNAL CIRCUIT

40. CIRCUITS OF AMYGDALA
 Serves to integrate information processing between
prefrontal/ temporal association cortices and the
hypothalamus.
 The amgdala has two major outputs
 Dorsal route- via stria terminalis projects to the septal
area and hypothalamus
 Ventral route- via ventral amygdalofugal pathway.

41. AMYGDALO-SEPTAL PATHWAY

42. AMYGDALA BASAL GANGLIA
CIRCUIT

43. FUNCTIONS OF THE
LIMBIC SYSTEM
 OLFACTION:
 limbic structures are closely related to the
olfactory cortex and have a role in the
processing of olfactory sensation
 Amygdala is involved in the emotional
response to smell while the entorhinal cortex
is concerned with olfactory memories

44.  APPETITE AND EATING BEHAVIOUR:
 Amygdala plays a role in food choice and emotional
modulation of food intake.
 SLEEP AND DREAMS:
 PET and MRI have shown that the limbic system is
the most active brain areas during the process of
dreaming.
 Probably interweaves unconscious primal emotions
with conscious cognitive thoughts
 The suprachiasmatic nucleus of the hypothalamus
generates the circadian cycle. Controls sleep-wake
cycle.

45.  EMOTIONAL RESPONSES:
 FEAR: fear responses are produced by the stimulation
of the hypothalamus and amygala. Amygdala is also
involved in fear learning.
 RAGE AND PLACIDITY: Rage reponses to minor
stimuli are observed after removal of the neocortex.
Destruction of the the ventromedial hypothalamic
nuclei and septal nuclei also induces rage.

46.  AUTONOMIC AND ENDOCRINE RESPONSES TO
EMOTION:
 Limbic stimulation causes changes in respiration and
blood pressure.
 The stimulation of the cingulate gyrus and
hypothalamus can elicit autonomic responses
 The fear and rage responses mediated by the limbic
system cause stimulation of various parts of the
hypothalamus, especially the lateral areas and
produce diffuse sympathetic discharge. The massive
sympathetic discharge during stress is called the —
fight or fright response“.
 Stress via cortical and limbic connections causes
release of corticotropin-releasing hormone (CRH) from
the paraventricular nuclei of the hypothalamus.

48.  SEXUAL BEHAVIOUR:
 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)

49.  REWARD AND PUNISHMENT:
 electrical stimulation of certain limbic area pleased or
satisfies the animal or cause terror, pain, fear,
defense, escape reactions
 Reward centers: along the course of the medial
forebrain bundle and lateral and ventromedial nuclei
of the hypothalamus
 Punishment centers: central gray area surrounding the
aqueduct of sylvius in the mesencephalon and
extending upward into the periventricular zones of the
hypothalmus and thalamus

50.  MEMORY:
 Emotional memory: Amygdala is involved in consolidation
and retrieval of emotional memories. also involved in the
acquisition, extinction and recovery of fears to cues and
contexts. Hippocampus is critical for long-term, declarative
memory storage.
 Medial temporal lobe memory system: include the
hippocampus and adjacent cortex, the parahippocampal
regions (PHG) . This memory system is involved in the
storage of new memories
 Diencephalic memory system: consists of the
hypothalamus, mammillary body and the dorsomedial
nucleus of thalamus. This circuit is important for the
storage of recent memory; a dysfunction of this circuit
results in Korsakoff’s syndrome.

51.  SOCIAL COGNITION:
 refers to thought processes involved in understanding
and dealing with other people.
 Social cognition involves regions that mediate face
perception, emotional processing; theory of mind
(TOM); self-reference and working memory.
 Together, the functioning of these regions would
support the complex behaviors necessary for social
interactions.
 Limbic structures involved are the cingulate gyrus and
amygdala

52. CLINICAL
IMPLICATIONS

53.  TEMPORAL LOBE EPILEPSY:
 Most common epilepsy in adults and is most often
caused by hippocampal sclerosis. Seizures that occur
in these areas are called psychomotor seizures.
 Temporal lobe epilepsy may include: abnormal
sensations (uncinate fits), repeated involuntary
movements, memory loss, hallucinations and
disorders of recall and recognition
 Although anticonvulsant drugs are often given to
control the seizures they maybe ineffective. In these
cases neurosurgical removal of the focus may provide
excellent seizure control

54.  LIMBIC ENCEPHALITIS:
 Paraneoplastic syndrome reported in carcinoma of the
lung, breast etc. Mechanism is unknown but manifests
as encephalitis. Afflicted patients develop sub acute
onset of memory loss, dementia, involuntary
movements and ataxia.
 DEMENTIA:
 Degenerative changes in the limbic system likely have
a role in the genesis if neurodegenerative diseases
esp. Pick’s disease and Alzheimer’s disease. Marked
atrophy is found most notably the dentate gyrus and
hippocampus.

55.  ANXIETY DISORDERS:
 Maybe result of a failure of the ant. Cingulate and
hippocampus to modulate the amygdala.
 SCHIZOPHRENIA:
 Studies have shown reduced limbic volumes. There is
involvement of papez circuit. The other circuit involved
is the basolateral circuit which mediates the social
cognition deficits in schizophrenia.
 AFFECTIVE DISORDERS:
 decreased prefrontal and anterior cingulate activity in
affective disorders.

56.  ADHD:
 The enlarged hippocampus in children and
adolescents with ADHD may represent a
compensatory response to the presence of
disturbances in the perception of time, temporal
processing and stimulus-seeking associated with
ADHD.
 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.

57.  KLUVER-BUCY SYNDROME:
 Kluver-Bucy syndrome results due to a bilateral destruction
of the amygdaloid body and inferior temporal cortex.
 Major characteristics of this syndrome include: hyperorality,
hyper sexuality, psychic blindness, personality changes,
usually with the development of abnormal passivity or
docility.
 Combination of at least 3 or more of the symptoms suggest
the syndrome
 This disorder may be caused by many conditions including
cerebral trauma; infections, Alzheimer’s disease and other
dementias; Niemann-Pick disease and cerebrovascular
disease

58.  The psychic blindness observed presumably results
from damage to the amygdalae, which usually
functions as a site of transfer of information between
sensory association cortex and the hypothalamus
 After damage, visual stimuli can no longer be paired
with affective responses
 Treatment:1) carbamazepine- potent inhibitor of
amygdaloid kindling. Useful agent for eliminating
some of the the symptoms. 2) leuprolides- decrease
sexual behavior 3)antipsychotics like haloperidol to
reduce behavioral abnormalities

59.  KORSAKOFF PSYCHOSIS:
 Caused by damage to mammillary bodies,
dorsomedial nucleus of thalamus
 Due to thiamine deficiency in chronic alcoholics
 Associated with impairment of recent and remote
memory. (recent> remote)
 Immediate recall is usually preserved.
 Confabulation maybe present and marked

60. THE END
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