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Chapter: Medical Physiology: Behavioral and Motivational Mechanisms of the Brain-The Limbic System and the Hypothalamus

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Function of the Limbic Cortex

The most poorly understood portion of the limbic system is the ring of cerebral cortex called the limbiccortex that surrounds the subcortical limbic structures.

Function of the Limbic Cortex

The most poorly understood portion of the limbic system is the ring of cerebral cortex called the limbiccortex that surrounds the subcortical limbic structures. This cortex functions as a transitional zone through which signals are transmitted from the remainder of the brain cortex into the limbic system and also in the oppo-site direction. Therefore, the limbic cortex in effect functions as a cerebral association area for control ofbehavior.

Stimulation of the different regions of the limbic cortex has failed to give any real idea of their functions. However, as is true of so many other portions of the limbic system, essentially all behavioral patterns can be elicited by stimulation of specific portions of the limbic cortex. Likewise, ablation of some limbic cortical areas can cause persistent changes in an animal’s behavior, as follows.

Ablation of the Anterior Temporal Cortex. When the anteriortemporal cortex is ablated bilaterally, the amygdalas are almost invariably damaged as well. This was discussed earlier; it was pointed out that the Klüver-Bucy syndrome occurs. The animal especially develops consummatory behavior: it investigates any and all objects, has intense sex drives toward inappro-priate animals or even inanimate objects, and loses all fear—and thus develops tameness as well.

Ablation of the Posterior Orbital Frontal Cortex. Bilateralremoval of the posterior portion of the orbital frontal cortex often causes an animal to develop insomnia asso-ciated with intense motor restlessness, becoming unable to sit still and moving about continuously.

Ablation of the Anterior Cingulate Gyri and Subcallosal Gyri. Theanterior cingulate gyri and the subcallosal gyri are the 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. Therefore, the animal can become vicious and much more subject to fits of rage than normally.

Summary. Until further information is available, it isperhaps best to state that the cortical regions of the limbic system occupy intermediate associative positions between the functions of the specific areas of the cere-bral cortex and functions of the subcortical limbic struc-tures for control of behavioral patterns. Thus, in the anterior temporal cortex, one especially finds gustatory and olfactory behavioral associations. In the parahip-pocampal 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 asso-ciations occur.


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