Introduction Investigations of the physiological substrate of behavioral and vegetative mechanisms in the brain have drawn attention to the interdependence of large aggregates of neurons acting upon one another in dynamic equilibrium. Recent interest in the rhinencephalic pathways, as they relate to behavior9,40,52,53,67,73,82and autonomic functions,3, 17,19,22,28,32,39,41,42,49-52,58-62and in the reticular activating system, with its contribution to the maintenance of consciousness,4,24,63, 72,83has led to the present study designed to interrupt these two systems at the junction of the forebrain and the diencephalon. Our attention was originally drawn to this area by the work of Heath and his associates.38 Anatomical observations by Rose and Woolsey78(1949) and electrophysiological studies by Jasper47(1949) suggested that the nucleus reticularis, which forms the oral pole and surrounds most of the thalamus, was well situated to relay widespread cortical responses from the diffuse thalamic projection system. Subsequent observations