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SummaryA study of the results of some 660 cases of stereotactic tractotomy shows that these have been consistent through a 12-year period, more than 50°4 of cases of resistant depression can be set free of medical care and another 25%4 at least can be improved. Comparable results are also obtained in obsessional illness and anxiety states, particularly those in which there is a depressive component.The original localization of the target site described in 1964 has not required modification but pathological studies and anatomical research has revealed new features concerning the anatomical connections affected by this operation.The lesion beneath the head of the caudate nucleus does not extend quite so far as the substantia innominata and should therefore be called subcaudate tractotomy. Connections from the anterior cingulate region and posterior orbital cortex are severed at this site but amygdalo-hypothalamic fibres are not interrupted directly, however; the projection from the amygdala to the dorsal median nucleus sends a radiation to the posterior orbital cortex which is divided here. In addition, important projections from frontal cortex to hypothalamus which bring the external milieu into association with the limbic system pass downwards through the target area beneath the head of the caudate nucleus and are also divided at this point, the localized lesion, therefore, produces a marked effect upon fibres which are concerned in emotional activity. The wellnigh specific effect in cases of depression raises the question whether the operation acts by modifying the intensity of emotional reactivity through limbic connections or has a more specific effect upon the cause of abnormal reactivity through fronto-hypothalamic connections exerting an influence on monoamine production in the hypothalamus.THE extension of the field of psychosurgery, which has resulted from the development of precise localized procedures and atraumatic methods of operation under stereotactic control, has yielded information concerning the effect of operation at

Stereotactic surgery has provided a means of producing accurate lesions at selected points in the nervous system where concentrations of nerve cells or fibre pathways possessing specific functions permit some small area of anatomical destruction to produce widespread physiological effects. The value of this method in relation to motor and sensory activity is illustrated by the results of thalamotomy in the treatment of Parkinsonian tremor and by stereotactic division of the spinothalamic tract in the cervical cord for the relief of incurable pain. The accuracy of approach and minimal disturbance of tissue ensures that the beneficial effects of these operations are produced in isolation without associated disfunction in the nervous system. That a similar principle can be applied in relation to the control of emotion has been shown in cases of intractable psychoneurosis treated by the operation of bifrontal stereotactic tractotomy in the substantia innominata (Knight, 1964). Owing to the influence of emotion in psychoneurotic states it is possible to influence many syndromes satisfactorily by operation at a site where connections of the limbic system concerned with instinctive and emotional activity rather than cognitive processes converge to a point beneath the head of the caudate nucleus, thereby producing a reduction in the intensity of emotional reaction without undesirable personality change or post-operative epilepsy. It is felt that it would be useful to summarize the anatomical features in order that the differences between this operation and the old leucotomy procedure can be generally appreciated. It is particularly among cases of chronic and recurrent depression that this form of surgery can be most usefully employed.