Limbic System – General and Hypothalamus

Prof. K. Sivapalan

Lymbic system- Hypothalamus 223-03-14

Structure of Limbic System.• Border structures around the base

of cerebrum form the lymbic system.

• They are cortical tissue around the hilum of the cerebral hemisphere and associated deep structures

• The structures include hypothalamus, amygdala, hippocampus, and septal nuclei, para olfactory area, anterior nucleus of the thalamus and portions of basal ganglia.

Lymbic system- Hypothalamus 323-03-14

Lymbic system- Hypothalamus 423-03-14

Evolution.

Lymbic system- Hypothalamus 523-03-14

Functions of the Lymbic System

• Limbic system is concerned with generation and expression of emotions and controls emotional behavior and motivational drives.

• Stimulation of certain areas increases the excitability of cerebrum and spinal cord.

• A characteristic of limbic circuit is its prolonged after discharge following stimulation.

• This may explain in part the fact that emotional responses are generally prolonged and outlast the stimuli that initiate them.

Lymbic system- Hypothalamus 623-03-14

Emotion

• Cognition- an awareness of sensation and its cause.

• Affect- feeling it.• Conation- urge to take action.• Physical changes- change in blood pressure,

heart beat, respiration etc.

Lymbic system- Hypothalamus 723-03-14

Reward and Punishment Areas.

• Also described as satisfaction or aversion.• Stimulation of the reward centre satisfies the animal.• Stimulation of punishment centers cause terror, pain,

fear, defense, or escape reactions.• Excessive stimulation of reward centers can generate

sense of punishment.• Excessive stimulation of punishment centers can

make the animal sick and even lead to death.

Lymbic system- Hypothalamus 823-03-14

Rage

• Defense posture• Extend claws.• Lift tail.• Hiss• Spit• Growl• Develop piloerection• Wide open eyes• Dilated pupils.

• Slightest provocation results in savage attack.• Stimulation of punishment centers provoke

rage • stimulation of reward centers provoke

tameness-placidity

Lymbic system- Hypothalamus 923-03-14

Reward and Punishment in Learning and Memory

• Stimuli that cause neither of these are not remembered.

• The limbic system has much to do with selecting the information to be learnt and thrown away.

• About 99% of the input is thrown away and only 1% is learnt.

Lymbic system- Hypothalamus 1023-03-14

Behavioral Functions of Hypothalamus.

Effects of stimulation-• Lateral hypothalamus- thirst, eating, increase in the

general level of activity sometimes leading to rage and fighting.

• Venteromedial- satiety, decreased eating and tranquility.

• Periventricular- fear and punishment reactions.• Anterior and posterior areas and other areas in

hypothalamus – sexual drive.