The limbic system includes structures involved in emotion processing and memory formation. It contains nuclei such as the hippocampus, amygdala, and septal nuclei, as well as connecting tracts. The hippocampus forms memories and is connected to the amygdala and septal nuclei. The amygdala processes emotions and regulates autonomic functions. Stimulation of the septal nuclei produces pleasurable sensations. Together, these structures form circuits like the circuit of Papez that are important for emotional processing and memory.

1. Limbic System
Dr. Mohammad hussein
2nd May 2008

3. Limbic System
Name is derived from the Latin word limbus,
meaning a border,
In1878 introduced by the neuroanatomist
Pierre Paul Broca to describe the ring of gyri
that surround the brain stem.
In 1937, James Papez described a circuit that
he suggested formed the anatomical site for
emotion (CIRCUIT OF Papez).

15. limbic system includes
I. Primary nuclei
II. Cortical areas
III. Connecting
tracts

16. I. Primary nuclei
1. hypothalamic nuclei
2. amygdaloid nucleus
3. hippocampus
4. septal nuclei
5. thalamic nuclei:
anterior,
lateral dorsal,
medioventral nuclei
6. mamilllary bodies
7. superior central nucleus
8. ventral tegmental area
9. raphe nucleus

17. 1. cingulate gyrus
2. hippocampal formation:
a) dendate nucleus
b) hippocampus
c) parahippocampal gyrus
3. olfactory tubercle
4. secondary olfactory area
5. subcallosal gyrus
6. indusium griseum
7. paraterminal gyrus
II. Cortical areas

18. III. Connecting tracts
1. cingulum
a) hippocampus to cingulate gyrus
2. anterior commissure
3. dorsal longitudinal fasciculus
4. stria terminalis
a) hypothalamus to amygdala
5. stria medullaris thalami
6. amygdalofugal bundle
a) hypothalamus to amygdala
7. fornix
a) hypothalamus to hippocampus
8. medial forebrain bundle
a) hypothalamus to septal nuclei
b) involved in the positive reinforcement of behaviours
9. mamillothalamic tract
a) mamillary bodies (hypothalamus) to anterior thalamic
nucleus

19. circuit of
Papez
· the largest components
contain a ring of
interconnected neurons
called the circuit of Papez,
which links the neocortex to
the limbic system via the
cingulate gyrus.
Compents;
1.hippocampus
2.mammillary
. body
3.thalamus
4.cingulate gyrus

21. circuit of Papez
input:
– neocortex
– thalamus
– septal area
– raphe nuclei
– ventral tegmental
area
– catecholamine
nuclei of the reticular
formation
output:
– neocortex
– regions of the
reticular formation
that influence the
autonomic system
indirectly

22. 1.The Hippocampus
‫البحر‬ ‫فرس‬
Hippocampus;

23. 1.The Hippocampus
‫البحر‬ ‫فرس‬
Hippocampus;

24. The hippocampal formation
hippocampal formation is made up of ;
1. the hippocampus, and
2. the neighboring temporal regions, namely the
dentate gyrus
3. the subiculum.
The subiculum is located in the
parahippocampal gyrus. In addition, the
hippocampal region includes the entorhinal
area in the parahippocampal gyrus.

26. The hippocampus is recognized
anatomically as a medial bulge in the
temporal horn of the lateral ventricle. The
bulge is caused by the invagination (turning
in) of the ventricular wall. This invagination is
the result of the infolding called the
hippocampal fissure.

27. The dentate gyrus is a narrow band along
the medial aspect of the hippocampus. The
dentate gyrus and hippocampus are part of
the allocortex, which has a laminar
(layered) structure similar to the neocortex,
although with less layers and somewhat
more simplified.

28. The hippocampus is a
bilobate structure;
the two sides
communicate through
the commissural fibers.
The pathways that
constitute the
hippocampus-
entorhinal area-
hippocampus circuit
are all excitatory.

29. Connections;
inputs (afferents)
main inputs (afferents) come from
1. the entorhinal area of the hippocampal
gyrus,
2. there is a smaller input from the septal
nuclei.
The pathway from the entorhinal area to the
hippocampus is termed the perforant
path,

30. Connections;
efferent
efferent fibers mainly to;
1. the entorhinal area,
2. the subiculum, and
3. the septal nuclei.
Therefore the hippocampus acts directly
mainly on neighboring brain areas.

31. Neurotransmitters &hippocampus
fibers from the septal nuclei to the
hippocampus release acetylcholine.
The raphe nuclei of the midbrain
project 5-HT fibers to the hippocampus.
noradrenergic afferents project to the
hippocampus from the locus ceruleus.

32. 2.The Septal Nuclei
septal nuclei (septal
region) consists of a
small area of brain in
the telencephalon, in
the medial wall of the
cerebral hemisphere
rostral to the anterior
commissure and
medial to the lateral
ventricles.

33. Components;
subdivided into two
main parts, the medial
and lateral septal nuclei.
The medial septal
nucleus consists of
relatively large neuronal
cell bodies, while the
lateral nuclear cell bodies
are smaller.

34. The septal region also includes the bed
nucleus of the stria terminalis, the
triangular septal nuclei, the
septohippocampal and the
septofimbrial nuclei, and the diagonal
band of Broca.

35. Connections;
I. Afferent;
1. the hippocampus via the fornix.
2. amygdaloid nuclei via the ventral amygdalofugal
pathways and the stria terminalis
3. the ventral tegmental nuclei in the midbrain.
4. cingulated gyrus, and reciprocal inputs from the
hypothalamus and pre-optic region via the medial
forebrain bundle

36. 1. to the hippocampus via the
fornix,
2. to the ventral tegmental
nuclei via the medial
forebrain bundle,
3. to the habenular nucleus,
4. to the medial thalamic nuclei
via the stria medullaris
thalami,
5. to the lateral hypothalamus
and preoptic region.
Connections;
II. Efferent;

37. Connections;

38. although relatively small in size, appears to have
several diverse and important functions.
The human septal nuclei have been stimulated
and this is reported to produce intensely
pleasurable sensations, and a sensation of
well being. In other species, this area is possibly
an important site of reward reactions.
If the septal area is destroyed, this seems
to remove an inhibitory influence on rage,
and the animal responds with signs of
displeasure, so called ‘septal rage ‫’الغضب‬.
Function;

39. The neurotransmitter that may mediate the
pleasurable response in this area is
dopamine.
There is evidence from studies in humans
that antipsychotic drugs may produce their
effects by modifying the dopaminergic
inputs to the septal nuclei.
Function;

40. 3.The Amygdaloid Complex
The amygdaloid complex, or
the amygdala ; ‫لوزة‬,

41. amygdale;
an almond-shaped
collection of nuclei, is
found in the temporal
lobe, beneath the uncus.
It comprises the basal,
central, lateral, and
superficial groups of
nuclei. In addition to the
afferent and efferent
connections, there are
several intrinsic
connections between the
amygdaloid nuclei.

42. amygdale;
nuclei have been grouped as the larger basolateral and
smaller corticomedial nuclei, which include the central
nucleus.
This grouping is based on function and connections;
 the basolateral nuclear group has connections with the striatum,
thalamus, and the cerebral cortex,
 the corticomedial group is connected mainly with the
hypothalamus, central visceral nuclei, and the olfactory bulb.
The basolateral nuclear group increases in size up the
evolutionary ladder ‫م‬‫االطولو‬ ‫م‬ّ‫السل‬ , and is relatively large in
the human brain. The corticomedial group may be more
concerned with autonomic function, while the basolateral
group may mediate some conscious processes related to
frontal and temporal lobe activity.

43. Connections;

44. Functions of the Amygdaloid
Complex
Knowledge of the functions of the amygdaloid
nuclei has been derived from observations of
behavior after ablation or stimulation of the
amygdala in animals or after damage to the
amygdala in humans.
It is difficult precisely to assess the contribution of
the various amygdaloid nuclei to any behavioral
or autonomic response, due to the diffuse
anatomical relationships within the amygdala. In
animals, stimulation of the amygdale produces
stereotyped behavioral responses.

45. 1. stimulation of the basolateral group of nuclei
produces signs of increased attention in cats. The
pupils dilate and the animal lifts its head and looks
around with what appears to be increased curiosity
about its immediate surroundings. In particular, it turns
its head to the side opposite from that in which the
electrode is implanted. Concomitant with these
behavioral signs, there are activational changes in the
EEG. If the intensity of the stimulus is increased, this
produces aversive behavior. The animal snarls‫ة‬ ‫الزمجل‬,
backs away, or may even attack.

46. 2. Ablation (bilateral surgical removal) of the temporal
lobes, which include the hippocampal formations as
well as the amygdala, results in docile ّ‫ل‬‫ل‬‫س‬
:
‫و‬ ‫ل‬‫ل‬‫م‬
behavior in monkeys.
There is an apparent deletion of any rage or fear
response to stimuli which evoked these responses
prior to the operation. The operation produces aberrant
behavior as well.
Monkeys exhibited increased, and, in some cases,
apparently bizarre sexual behavior; They attempted to
mount others of the same sex, of other species, and
inanimate objects.
If the lesions were confined to areas within the amygdala,
without discernible damage to the hippocampal
formation, the animals exhibited docility without the
expression of aberrant sexual behavior. The aberrant
sexual behavior may have been due to destruction of
brain areas adjacent to the amygdala.

47. • It should be noted, nevertheless, that the
amygdaloid nuclei of both sexes are rich in
estrogen receptors, which strongly suggests that
the amygdaloid nuclei are targets for the sex
hormones.
• Experiments with monkeys suggest a memory
role for the amygdala. If the amygdala are
lesioned, then monkeys lose the ability to
associate objects and their implications. For
example, if monkeys are taught that an object is
associated with a punishment, they lose this
memory after lesions of the amygdala.

48. In humans, stimulation of the amygdale
during brain surgery under local
anesthesia produces sensations of
anxiety and fear.
Similar feelings are elicited if the temporal
lobe is stimulated; it is known that the
temporal lobe projects to the amygdala.
There is in humans a condition called the
Klüver-Bucy syndrome, caused by the
bilateral lesioning of the amygdaloid
nuclei.

49. Klüver-Bucy syndrome
Lesions may be caused through temporal lobe
surgery for epilepsy, or through trauma.
It is unclear whether the syndrome is due purely to
injury to the amygdala or to adjacent areas as
well.
The patient may no longer recognize objects by
sight (visual agnosia), touch (tactile agnosia), or
by hearing (auditory agnosia). Patients are
generally docile. They may eat to excess
(hyperphagia), and eat objects that are not
food.
There is also sometimes overt, and inappropriate
and antisocial, hypersexuality.

50. The Cingulate Gyrus
The cingulate gyrus is continuous
with the parahippocampal gyrus,
and runs around the splenium of the
corpus callosum.
The cingulate gyrus lies below the
cingulate sulcus.
The cingulate gyrus and the
parahippocampal gyrus are linked
by the fibers of the cingulum.
The cingulated gyrus is a form of
primitive cortex, with three layers
instead of the six layers of the
neocortex. It is a major part of the
circuit of Papez

51. soooooon
Connections;

52. ‫حسين‬ ‫محمد‬
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