3) Limb us means border. French physiologist Paul B recused the term LIMBIC LOBE to designate the border of neocortex and the primitive brain Originally this was called rhirie nee p halo n and was thought to be concerned with olfaction (Sense of smell) only. Limbic lobe consists of part of cerebral cortex. Mclean included subcortical structures and called the whole complex LIMBIC SYSTEM It is concerned with emotions and emotions are involved in memory, social behavior, sexual behavior etc.

Limbic system influences copulatory reflexes which are integrated at spinal and brainstem levels and gives them the additional dimension of emotional pleasure or pain Thus the urge to copulate and coordination of the acts of male and female are dependent on limbic system. In lower animals learning is not necessary for successful mating In primates and man previous experience is necessary for successful mating In man sexual act is encephalized and hence emotional, social and psychological factors play a role Hence the development of emotions associated with monogamy, chastity, celibacy, illegitimacy, promiscuity etc.

Bilateral removal of temporal lobe, amygdala and hippocampus leads to excessive increase in the sexual drive irrespective of sex, species and even animate or inanimate nature of the object This has some relevance to psychopathic behavior in human beings.

4) Amygdala or amygdaloid nucleus is called window of the limbic system. Afferents from all structures of limbic system reach the amygdala.

Stimulation of amygdala in lower animals causes sense of olfaction In higher animals a) increase or decrease in blood pressure (BP) arid heart rate [HR] b ] Gastrointestinal [GIT] activity c) defecation d) micturition e] pilorechon f) pupillary dilation g) raising head 1) bending body.

Responses via hypothalamus: Some areas show fear when stimulated and like hypothalamus its stimulation also may cause sexual responses When temporal lobe is removed along with amygdala, KLUVER BUCY SYNDROME results It is associated with:

1. Excessive tendency to examine any object with mouth called ORAL TENDENCY.

11. Loss of fear.

111. Decreased aggressiveness iv) Changes in dietary habits Herbivorous may become carnivorous v) Psychic blindness called visual agnosia vi) Excessive sex drive where discretion with respect to maturity, species, sex and even Irving or non Irving is lost.

Stimulation of Amygdala stimulation causes rage and sympathetic effects whereas bilateral temporal damage leads to docility and lack of emotional expression In normal individuals there is a balance between rage arid docility Only major stimuli can disturb this balance and not the minor ones.

5) Emotional expression is associated with analysis of the situation, comparison with the past experience and assessment with respect to future effects This involves CEREBRAL CORTEX and limbic system.

Ablation of anterior portion of cingulate gyrus and subcallosal gyrus is associated with rage reaction and the animal becomes dangerous.

6) HIPPOCAMPUS (Amnions horn) the cortex of hippocampus is allocortex which is 3 layered. It is important for emotions in an indirect manner. Hippocampus means a small marine animal called sea horse Hippocampus has connections with various systems through fornix. Various effects caused by the lesions of hippocampus are:

a) Ability to learn new tasks or perform the tasks learned previously is lost. This is called antigrade amnesia i.e. inability to Leam. Thus it is important in consolidating memory.

b) Sometimes there is retrograde amnesia i.e. loss of memory of the past events.

Bilateral hippocam pal lesions cause loss of recent memory which is oh served in aging also. Thus ageing may involve degeneration of limbic system Past memory is not lost. This is one of the reasons why aged people seem to possess lesser intensity of emotions and appear to have become self centered or selfish.

7) Dopamine and Norepinephrine [N Ej for rage reaction Fall in NE causes depression and rise in NE causes elevation of mood Antidepressant drugs may increase biological amines in brain.

8) Orbitofrontal cortex is related to sleep and restfulness as ablation results in insomnia and restlessness. This may play a role in causation of anxiety and induce sleeplessness, sometimes desirably and sometimes dangerously.

9) If median forebrain bundle is stimulated there is motivation The organism presses the lever which stimulates this part electrically. This is important as when all other factors are same it is the motivation which plays a major role in performance. It is essential to find out other factors affecting motivation as 111 as simple means to develop motivation.

Connections

1) PAPEZ CIRCUIT: Papez 1937. Hippocampus -> Fornix -> Mamillary bodies -> Anterior nucleus of thalamus -> Thalamocortical fibers via internal capsule -> Cingulate gyrus -> via cingulum -> parahippocampal and dentate gyrus.

The cortex of the cingulate gyrus is juxtallocortex or paleocortex 4 to 5 layered {Majority of the cerebral cortex is 6 layered and is called lsocortex).

2} M am lllaryb o dies to dorsomedial nucleus of the thalamus and reticular nucleus of the thalamus to non limbic portion of cortex (prefrontal and temporal not precentral) Conduction is fast a and b are called nontemniscal pathway and convey information from ascending reticular activating system [ARAS].

3] Afferents from all viscera and body walls i.e. practically all sensations are relayed to hippocampus and its electrical activity is increased Hypothalamus gets information from external environment to hippocampus via mamiilo thalamo cingulo fomico hippocampal pathway.

The connections show REPETITIVE DISCHARGE OR AFTER DISCHARGE Hence emotional experiences linger in mind for long time and appear even in dreams.

Conduction is slow Thus emotions are not as quick as a withdrawal reflex or a stretch reflex Such quick or fast reflexes take place without emotional experiences.