I. GENERAL CONSIDERATIONS.Diagram of the neurone supply of the optic thalamus. Motor disorder the most frequent effect of optic thalamus lesions, except those extensive enough to produce hemianesthesia. Hyperkinesis and neural tissue-simplification. A possible structural correlate of depression.II. MATERIAL OF THE STUDY, WITH BRIEF REMARKS UPON THE THALAMUS.Cases of totally destructive or focally destructive lesions omitted from consideration.- Endeavor to study cases of diffuse chronic conditions of partial loss or absence of mechanisms (atrophy, aplasia) such that the throughroutes for sensory impulses are preserved. Impossibility at present of imitating such lesions by experimental methods such as extirpation by scalpel or by electrolysis. Summary of structures whose lesions were reviewed. Summary of symptoms reviewed.III. HYPERKINESIS AND DIFFUSE CHRONIC THALAMIC LESIONS.Hyperkinetic symptoms are here defined as including psychomotor excitement, violence, destructiveness, homicidal acts, irritability and exaltation.24 of 29 cases showed one or more of these hyperkinetic symptoms. Study of the exceptions shows that two cases had also lesions of the thalamocortical neurone systems, that one case was an instance of pulvinar lesions, and that one was a case with lesions hardly extensive enough (“vacuoles”) to be included. But one case out of the remaining 25 failed to show such symptoms (a stuporous general paretic). Comparison of this group with a group of 261 cases with normallooking brains shows that the thalamic series excels the normallooking brain series in violence, homicide, and irritability. On the other hand the thalamic series showed fewer depressive symptoms (including suicidal tendencies and apprehensiveness) than the normal-looking brain series.IV. GENERAL RESULTS.&NA;