2. LEARNIBG OBJECTIVES
• Brief physiological anatomy of limbic system.
• Describe the roles of limbic system.
• Discuss especially the roles of
– hippocampus
– amygdale
– various reward and punishment centers.
• Discuss the lesions of various parts of limbic
system,with neurophysiologic basis and
effects.
3. LIMBIC SYSTEM
• Limbic:border
• Refers to a ring of gray matter on the medial
aspect of the cerebral hemispheres.
4.
5.
6. LIMBIC SYSTEM
• the entire neuronal circuitry that controls
emotional behavior and motivational drives.
• Network of structures is associated with
emotions, basic survival and sociosexual
behavioral patterns, motivation, and learning.
7. Motivation
• is the ability to direct behavior toward specific
goals.
• Some goal-directed behaviors are aimed at
satisfying specific physical needs related to
homeostasis:Homeostatic drives
• As an example, the sensation of thirst,hunger.
10. Hypothalamus:
• Major part
• Vegetative roles
• Behavioral control
• governs the involuntary internal responses of various
body systems in preparation for appropriate action to
accompany a particular emotional state. For
example, the hypothalamus controls the increase of
heart rate and respiratory rate, elevation of blood
pressure, and diversion of blood to skeletal muscles
that occur in anticipation of attack or when angered.
• these preparatory changes in the internal state require
no conscious control
11. • Stimulation in the lateral hypothalamus :
thirst and eating, overt rage and fighting.
• Stimulation in the ventromedial nucleus and
surrounding areas mainly causes effects
opposite to those caused by lateral
hypothalamic stimulation—that is, a sense of
satiety, decreased eating, and tranquility.
12. • Stimulation of a thin zone of periventricular
nuclei, located immediately adjacent to the third
ventricle (or also stimulation of the central gray
area of the mesencephalon that is continuous
with, this portion of the hypothalamus), usually
leads to fear and punishment reactions.
• Sexual drive can be stimulated from several areas
of the hypothalamus, especially the most anterior
and most posterior portions of the hypothalamus
13. Effects Caused by Hypothalamic
Lesions.
• Bilateral lesions in the lateral hypothalamus :decrease drinking and
eating almost to zero, lethal starvation,extreme passivity of the
animal as well, with loss of most of its overt drives that are
observable emotional expressions (for example, laughing,
crying, or blushing).
• Bilateral lesions of the ventromedial areas of the
hypothalamus : excessive drinking and eating ,hyperactivity and often
continuous savagery (cruelty) along with frequent bouts of extreme
rage on the slightest provocation.
• Stimulation or lesions in other regions of the limbic
system, especially in the amygdala, the septal area,
and areas in the mesencephalon, often cause effects
similar to those elicited from the hypothalamus.
14. Anterior nucleus of thalamus
• Afferent connections:
– Mammillothalamic tract,cingulate gyrus and
hypothalamus
• Efferent connections:
– Cingulate gyrus,hypothalamus
• Functions:
– Emotional tone i-e attitude,mechanism of recent
memory.
15. Mamillary bodies
• They are connected to other parts of the brain
• 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'.
16.
17. • Mammillotegmental tract: terminates in
reticular formation of mid brain.
• 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.
18. Dorsomedial nucleus of thalamus
• Prefrontal cortex,hypothalamus,other
thalamic
• Integration of somatic,visceral,olfactory
information and relation to subjective feelings
and emotional states
19. Damage to the mammillary bodies
• due to thiamine deficiency is implied in
pathogenesis ofWernicke-Korsakoff syndrome.
Symptoms include impaired memory, also
called anterograde amnesia.
• Lesions of the medial dorsal and anterior
nuclei of the thalami and lesions of the
mammillary bodies are commonly involved
in amnesic syndromes in humans.
20. Hippocampus
• The hippocampus and its adjacent temporal
and parietal lobe structures, all together
called the hipocampal formation.
• has numerous but mainly indirect
connections with many portions of the
cerebral cortex ,the amygdala, the
hypothalamus, the septum,and the mamillary
bodies
21. • Hyperexcitable:Prolonged discharges with slight
stimulus
• 3 layered structure
• Involved in sensations
– Almost any type of sensory experience causes
activation of at least some part of the hippocampus
– incoming sensory signals
– can initiate behavioral reactions for different purposes
22. • Seizures and hallucinations:focal epileptic
seizures with psychomotor effects
(olfactory,visual, auditory, tactile, and other
types of hallucinations that cannot be
suppressed as long as the seizure persists)
• pleasure,rage, passivity, or excess sex drive.
23. • Roles
– Learning(bilateral lesion,cant learn even names)
– Memory(working memory,consolidation of memory, declarative memory
functions)
– Evolutionary role (smell things to eat)
– Decision making for life and death
– It helps control corticosteroid production.
– It also has significant contribution to understanding spatial relations within
the environment.
• Lesion
– Anterograde amnesia
– No long term memory establishment.
– Lobes are removed for treatement of epilepsy.
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
31. • Involuntary movements
– (1) tonic movements, such as raising the head or
bending the body (2) circling movements (3)
occasionally clonic, rhythmical movements and (4)
different types of movements associated with
olfaction and eating, such as licking, chewing, and
swallowing.
• fear and punishment
• Sexual effects :erection(copulatory
movements, ejaculation, ovulation, uterine
activity, and premature labor).
32. Functions of the Amygdala
• behavioral awareness areas
• project into the limbic system one’s current status in
relation to both surroundings and thoughts.
• make the person behavioral response appropriate for each
occasion
• Relate environmental stimuli to coordinated behavioral
autonomic and endocrine responses seen in species-
preservation.
• Responses include:
Feeding and drinking
fighting behavior
Mating and maternal care
Responses to physical or emotional stresses
33. Kluver-Bucy Syndrome
• Results from bilateral destruction of temporal lobes or amygdala.
• Characteristics:
– Increase in sexual activity.
– Compulsive tendency to place objects in mouth.
– Changes in eating behavior.
– is not afraid of anything
– has extreme curiosity about everything
– forgets rapidly
– often has a sex drive so strong that it attempts to copulate with
immature animals, animals of the wrong sex, or even animals of a
different species.
• Although similar lesions in human beings are rare, afflicted people
respond in a manner not too different from that of the monkey.
34. Limbic cortex
• Cerebral association area for control of behavior.
• this ring of limbic cortex functions as a two-way
communication and association linkage between
the neocortex and the lower limbic structures.
• most poorly understood portion
• essentially all behavioral patterns can be elicited
by stimulation of specific portions of the limbic
cortex.
• ablation of some limbic cortical areas can cause
persistent changes in an animal’s behavior
35. Ablation of the Anterior Temporal
Cortex
• When the anterior temporal cortex is ablated
bilaterally, the amygdalas are almost invariably
damaged.
• Klüver-Bucy syndrome occurs.
36. Ablation of the Posterior Orbital
Frontal Cortex
• often causes an animal to develop insomnia associated with intense
motor restlessness, becoming unable to sit still and moving about
continuously.
• Function: The orbital frontal lobes act as the Senior Executive of the
social-emotional brain and exert tremendous inhibitory as well as
expressive influences on emotion and generalized arousal through
its massive interconnections with various limbic nuclie, the dorsal
medial nucleus of the thalamus and the reticular formation.
• When the orbital area is injured all aspects of emotional and
inhibitory behaviors may be compromised, and patients may display
disinhibition, manic-excitement, and internal utilization behaviors
(increased sexuality, orality).With complete destruction of the
orbital area, emotional and social functioning is abolished, but with
less extensive damage, rather than a loss of emotion there is a loss
of emotional control.
37. • cortical regions of the limbic system occupy intermediate
associative positions between the functions of the specific
areas of the cerebral cortex and functions of the subcortical
limbic structures for control of behavioral patterns.
• anterior temporal cortex: gustatory and olfactory
behavioral associations.
• In the parahippocampal gyri, there is a tendency for
complex auditory associations as well as complex thought
associations derived from Wernicke’s area of the posterior
temporal lobe.
• In the middle and posterior cingulate cortex, there is
reason to believe that sensorimotor behavioral associations
occur.
38.
39. Ablation of the Anterior Cingulate Gyri
and Subcallosal Gyri
• portions of the limbic cortex that communicate
between the prefrontal cerebral cortex and the
subcortical limbic structures.
• Destruction of these gyri bilaterally releases
the rage centers of the septum and
hypothalamus from prefrontal inhibitory
influence.
• Animal can become vicious i-e VIOLENT and much
more subject to fits of rage than normally.
40. Roles of prefrontal cortex
• higher levels of the cortex are also crucial for
conscious awareness of emotional feelings
• higher levels of the cortex, particularly the
prefrontal and limbic association areas, are
important in conscious learned control of innate
behavioral patterns
• prefrontal cortex formulates plans and guides
behavior, suppressing amygdala-induced
responses that may be inappropriate for the
situation at hand
41.
42. Medial forebrain bundle
• 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 inboth
directions, forming a trunk line
communication system between limbic system
and brainstem.
• Roles of reticular formation:mediate the
orders of hypothalamus,arousal.
43. • A second route of communication is through
short pathways among the reticular formation
of the brain
stem, thalamus, hypothalamus, and most
other contiguous areas of the basal brain.
44. Higer centers
• In executing complex behavioral activities such as
attack or mating, the individual must interact with the
external environment.
• Higher cortical mechanisms are called into play to
connect the limbic system and hypothalamus with the
outer world so that appropriate overt behaviors are
manifested.
• cortex provides the neural mechanisms necessary for
implementing the appropriate skeletal muscle activity
required to approach or avoid an adversary, participate
in sexual activity, or display emotional expression.
45. • Higher cortical levels also can
reinforce, modify, or suppress basic behavioral
responses so that actions can be guided by
planning, strategy, and judgment based on an
understanding of the situation.
46. Pathologies (lesions)
• Voracious appetite:very hungery
• Increased (perverse) sexual activity
• Docility:
Loss of normal fear/anger response,very calm
and easy to control
• Memory loss:
Damage to hippocampus portion
47. “Reward” and “Punishment” Function
of the Limbic System
• Electrical stimulation of certain limbic areas
• pleases or satisfies the animal or cause
terror, pain, fear, defense, escape reactions
• greatly affect the behavior of the anima
49. Reward Centers
• along the course of the medial forebrain
bundle
• lateral and ventromedial nuclei of the
hypothalamus.
• Less potent reward centers:
– the septum, the amygdala,certain areas of the
thalamus and basal ganglia, andextending
downward into the basal tegmentum of the
mesencephalon
51. Punishment Centers
• central gray area surrounding the aqueduct of
Sylvius in the mesencephalon and extending
upward into the periventricular zones of the
hypothalamus and thalamus.
• Less potent punishment areasare found in some
locations in the amygdala and hippocampus.
• Stimulation in the punishment centers can
frequently inhibit the reward and pleasure
centers completely.
52. Rage—Its Association with
Punishment Centers
• sudden and extreme anger
• Strong stimulation of the punishment centers
of the brain, especially in the periventricular
zone of the hypothalamus and in the lateral
hypothalamus, causes the animal to
53. Rage
(1) develop a defense posture,
(2) Extend its claws
(3) lift its tail
(4) hiss
(5) spit
(6) growl
(7) develop piloerection, wide-open eyes, and
dilated pupils.
54. Rage
• the slightest provocation causes an immediate
savage attack.
• expected from an animal being severely
punished.
55. rage phenomenon is held in check
mainly by
• ventromedial nuclei of the hypothalamus
• portions of the hippocampi and anterior
limbic cortex, especially in the anterior
cingulate gyri and subcallosal gyri, help
suppress the rage phenomenon.
57. Importance of Reward or Punishment
in Behavior
• Habituation Versus Reinforcement
– if the sensory experience does not elicit a sense of
either reward or punishment, repetition of the
stimulus over and over leads to almost complete
extinction of the cerebral cortical response.
ignores it.
– Reinforcement
• reward and punishment centers of the limbic
system select the information that we learn.
58. • Effect of Tranquilizers on the Reward or
Punishment Centers.
– chlorpromazine
59. Neurotransmitter Systems and the
Limbic System
• Dopamine: axons from ventral tegmental area
travel through the medial forebrain bundle and
connect with cingulate gyrus, hippocampus,
amygdala
• Serotonin: projections from the dorsal and median
raphe nuclei project diffusely and synapse on
limbic structures
• Noradrenergic system projects diffusely and
connects with limbic structures
• Cholinergtic system: projects diffusely and
connects with limbic system
60. • catecholamines are known transmitters in the
regions that elicit the highest rates of self-
stimulation in animals equipped with do-it-
yourself devices.
• Drug of abuse: Many abused drugs act by
enhancing the effectiveness of dopamine in the
“pleasure” pathways
– Amphetamine stimulates the release of dopamine
from dopamine-secreting neurons.
– is cocaine, which blocks the reuptake of sdopamine at
synapses
61. • A functional deficiency of serotonin or
norepinephrine or both is implicated in
depression
• Serotonin and norepinephrine are synaptic
messengers in the limbic regions of the brain
involved in pleasure and motivation
62. schizophrenia
• Various addictive compounds affect activity of the
dopamine transmission in the nucleus accumbens that is
ventral striatum or (mesolimbic) and frontal cortical
(mesocortical) systems.
• Additionally, these pathways appear to be functionally
unbalanced in patients with schizophrenia. It appears that
patients with schizophrenia have diminished dopamine
effects through mesocortical systems to the prefrontal
cortex. This could produce symptoms such as social
withdrawal and diminished emotional responsiveness.
Concurrently, there is a relative increase in dopamine
effects via the mesolimbic system to the ventral striatal
system, resulting in positive symptoms of delusions and
hallucinations.
65. • The hypothalamus plays an important role in generating
emotional behaviors…but
• The amygdala has been implicated in playing a prominent role in
integrating information and coordinating emotional behaviors in
response to sensory stimuli, events, and memories. These
findings were demonstrated in:
– Fear conditioning studies in rodents
– Monkey studies (Kluver-Bucy)
– Human neuroimaging and lesion studies
– Studies of memory modulation by hormones in lower animals.
66. • Reward processing occurs in distinct brain circuits.
– Stimulation of these circuits can provide powerful
reinforcement signals.
– Dopaminergic neurons in the ventral tegmental area provide a
learning signal that reflects a computation comparing the
reward received to the reward expected.
– Drugs of abuse act on reward circuits.
• Psychiatric disorders such as depression, anxiety disorders, and
addiction, all involve limbic system neural circuitry.
