LIMBIC SYSTEM
 Limbic:border
 Refers to a ring of gray matter on the medial aspect of
the cerebral hemispheres.
 Network of structures is associated with emotions,
basic survival and sociosexual behavioral patterns,
motivation, and learning.
Motivation
 is the ability to direct behavior toward specific goals.
 Homeostatic drives
 sensation of thirst,hunger.
Components
•Amygdaloid body
•Hippocampus
(“seahorse”)
•Cingulate gyus
•Parahippocampal gyrus
•Hypothalamus
•Mamillary bodies
•Anterior nucleus of
thalamus
•Medial forebrain
bundle
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 diversion of blood to skeletal muscles that occur in
anticipation of attack or when angered.
 Preparatory changes in the internal state require no
conscious control.
Concept of reward and punishment
center
Electrical self-stimulation and reward
 Stimulation in the lateral
hypothalamus
 Stimulation in the
ventromedial nucleus
 Concept of reward or
punishment center.
Anterior nucleus of thalamus
 Connections:
 Mammillothalamic tract,cingulate gyrus and
hypothalamus
 Functions:
 Emotional tone i-e attitude,mechanism of recent
memory.
Mamillary bodies
 Relay for impulses from amygdalae and hippocampi, via
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the mamillo-thalamic tract to the thalamus.
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.
Lesion:anterograde amnesia.
Dorsomedial nucleus of thalamus
 Prefrontal cortex, hypothalamus,other thalamic
nuclei.
 Integration of somatic,visceral,olfactory information
and relation to subjective feelings and emotional
states.
Hippocampus
 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.
 Seizures and hallucinations:focal epileptic seizures with
psychomotor effects.
 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.
 Lobes are removed for treatement of epilepsy.
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.
Amygdala stimulation produces emotional
behaviors through subcortical pathways
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 speciespreservation.
 Responses include:
Feeding and drinking
fighting behavior
Mating and maternal care
Responses to physical or emotional stresses
Limbic cortex
 Cerebral association area for control of behavior.
 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.
Ablation of the Posterior Orbital
Frontal Cortex
 Insomnia associated with intense motor restlessness.
 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.
 cortical regions of the limbic system occupy
intermediate associative positions :
 Anterior temporal cortex: gustatory and olfactory
behavioral associations.
 Parahippocampal gyri:complex auditory associations
,complex thought associations derived from Wernicke’s
area of the posterior temporal lobe.
 Middle and posterior cingulate cortex: sensorimotor
behavioral associations occur.
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.
 Releases the rage centers of the septum and
hypothalamus from prefrontal inhibitory influence.
 Animal can become VIOLENT and much more subject
to fits of rage than normally.
Roles of prefrontal cortex
 conscious awareness of emotional feelings
 prefrontal and limbic association areas, are important
in conscious learned control of innate behavioral
patterns.
 formulates plans and guides behavior, suppressing
amygdala-induced responses that may be
inappropriate for the situation at hand
Medial forebrain bundle
 Extends from the septal and orbitofrontal regions to
the brain stem reticular formation.
 Communication system between limbic system and
brainstem.
 Roles of reticular formation: mediate the orders of
hypothalamus,arousal.
Higer centers
 to connect the limbic system and hypothalamus with
the outer world
 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.
 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.
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
Rage
 the slightest provocation causes an immediate savage
attack.
 expected from an animal being severely punished.
 rage phenomenon is held in check mainly by
 ventromedial nuclei
 hippocampi
 anterior limbic cortex (anterior cingulate gyri and
subcallosal gyri)
Placidity and Tameness
 Tranquil,calmness
 reward centers are stimulated
Neurotransmitter Systems and the
Limbic System
Dopamine
2. Noradrenergic system
3. Cholinergtic system
4. Serotonin
1.
No functional signifance,just
historical
Functions
of limbic system
 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.
 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.