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Visually evoked unit responses of the tectum were studied in the squirrel monkey. The results showed that the superior colliculus had a definite functional laminar organization. Units responding to diffuse light were found in the upper part of the stratum grineum superficiale, units having antagonistically segregated receptive fields in the middle portion, and units sensitive to moving objects in the lower portion as well as in the stratum opticum. Retinotopic projection was also observed. The pretectal region contained mainly "tonic-on" and "inhibitory" units. No specific localization was observed in the distribution of these units.

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PONTANEOUS cerebral electrical potentials have been used clinically for prognosis following destructive cerebral lesions, and a persistently isoelectric electroencephalographic recording (EEG) has been considered one criterion of cerebral nonviability both for cessation of artificial maintenance of vital functions and for subsequent somatic organ transplantation. Prominent among causes of cerebral non-viability are those related to circulatory arrest, which include shock, arterial occlusive disease, cardiopulmonary insufficiency, and cardiac arrest. Diminution of cerebral blood flow as well as greatly increased intracranial pressure causes stagnant (ischemic) hypoxia, which in turn is reflected in profound EEG changes. These types of ischemic or anoxic cerebral insults may be reproduced experimentally and their effects on electrocortigraphic (ECoG) activity recorded. In such experiments, intrathoracic vascular occlusion causing immediate circulatory arrest has been produced to determine patterns of electrocortical silence, recovery, and the sensitivity of cortical electrical function related to survival. However, the preparation is not comparable to stepwise obliteration of the four major cervical vessels since simultaneous occlusion is difficult and a certain amount of cerebral damage can occur during experimental ligations, which make exact timing of anemia difficult. Also, a potentially large amount of collateral circulation exists. In man, for example, cases have been reported in which only minimal neurological dysfunction was caused following occlusion of all major cervical vessels, 8 although acute