LIMBIC SYSTEM

LIMBIC SYSTEM

Limbic:borderRefers 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.

Motivationis 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 partVegetative rolesBehavioral controlgoverns 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

Stimulation in the lateral hypothalamus

Stimulation in the ventromedial nucleus

Concept of reward or punishment center.

Electrical self-stimulation and reward

Anterior nucleus of thalamus

Connections:Mammillothalamic tract,cingulate gyrus and

hypothalamusFunctions:

Emotional tone i-e attitude,mechanism of recent memory.

Mamillary bodies

Relay for impulses from amygdalae and hippocampi, via 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 thalamusPrefrontal cortex, hypothalamus,other

thalamic nuclei.Integration of somatic,visceral,olfactory

information and relation to subjective feelings and emotional states.

HippocampusHyperexcitable:Prolonged discharges with

slight stimulus3 layered structureInvolved 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.

RolesLearning(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 deathIt 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 AmygdalaLarge 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 Amygdalabehavioral awareness areasproject into the limbic system one’s current status in

relation to both surroundings and thoughts. make the person behavioral response appropriate for

each occasionRelate environmental stimuli to coordinated behavioral

autonomic and endocrine responses seen in species-preservation.

Responses include:Feeding and drinkingfighting behaviorMating and maternal careResponses to physical or emotional stresses

Limbic cortexCerebral 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 GyriPortions 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 cortexconscious awareness of emotional feelingsprefrontal 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 centersto connect the limbic system and

hypothalamus with the outer worldneural 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 hungeryIncreased (perverse) sexual activityDocility:

Loss of normal fear/anger response,very calm and easy to control

Memory loss:Damage to hippocampus portion

Ragethe 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 TamenessTranquil,calmnessreward centers are stimulated

Neurotransmitter Systems and theLimbic System

1. Dopamine2. Noradrenergic system 3. Cholinergtic system4. Serotonin

No functional signifance,just historical

Functions of limbic systemThe 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 rodentsMonkey studies (Kluver-Bucy)Human neuroimaging and lesion studiesStudies 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.