The rarity of disturbances in sleep in patients with pure cortical lesions, as previously reported by us1 and by others, is in marked contrast to the frequency of their occurrence in patients with lesions involving both the cortex and the diencephalon.
Discrete lesions of the hypothalamus are known to cause interference with normal regulation of sleep. A brief review of the experimental and clinical evidence will be given in a later publication, concerned essentially with lesions at this level. Experimental evidence that lesions at the corticodiencephalic level may be responsible for disturbances in sleep is scanty. Clinical evidence, however, as furnished by the 25 cases in this presentation, and by the reports of other investigators, indicates that lesions at this level, involving either the centers or their pathways, are not of uncommon occurrence. In many of the cases to be discussed it was difficult to determine whether somnolence was