Mode of Action of Psychosurgery

Collectively, the brain's limbic system is composed of the hippocampus, amygdala, hippocampal and cingulate gyri, limen insulae, and posterior orbital regions of cerebral frontal lobes. This system, its components linked by nerve pathways, controls emotional expression, seizure activity, and memory storage and recall. Moreover, cerebral lobe limbic system connections from the dorsal convexity of a frontal lobe comprise two pathways running to the cingulate gyrus and hippocampus and the hypothalamus and midbrain. The frontal lobe orbital surface also projects to the septal area of the hypothalamus. The limbic brain architecture therefore yields two neurotransport circuits in a frontolimbic-hypothalamic-midbrain axis. These are a medial frontal, cingulate, hippocampus circuit (MFCHC) and an orbital frontal, temporal, amygdala circuit (OFTAC), which control hypothalamic autonomic and endocrine action. The MFCHC and OFTAC connect in the septa, preoptic area, midbrain, and hypothalamus.

The original Egas Moniz lobotomy divided the frontolimbic structures, and its bad effects were due to the disabling impairment of frontal lobe function. Psychosurgery on the anterior cingulate gyrus and on the thala-mofrontal bundle (bimedial leucotomy) divided different parts of the same main circuit. Orbital undercutting severs red nerve tracts running from the posterior orbital cortex to the limbic system. Although psychosurgery is currently an uncommon procedure, when it is performed, the methods used are lower medial quadrant leucotomy, making lesions just before the fourth ventricle; stereotactic-subcaudate-tractotomy, making lesions with rear halves in the subcaudate area; removal of the anterior two inches of the cingulate gyrus; and stereotactic limbic leucotomy, lesioning the lower medial frontal lobe quadrant. These operations cause varied endocrine and autonomic disconnections and are thus chosen to suit the mental condition being treated.

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