Frontal 'oculomotor" area in alert cat. I. Eye movements and neck activity evoked by stimulation

(1) Stimulation within cat frontal lobe elicited saccadic eye movements whose maximum velocity was significantly greater than that of normal spontaneous saccades. (2) The majority (90%) of stimulated cortical points yielded eye movements whose directions and amplitudes were independent of the position of the eye in the orbit. The direction of these eye movements depended on the site being stimulated, with a discrete and orderly representation of directions existing within the cortex. (3) A lesser number of cortical points (10%) yielded centering movements whose directions and amplitudes depended on the position of the eye in the orbit, rather than on the site being stimulated. (4) Evoked neck muscle activation frequently preceded evoked eye movements by some 15--30 msec. This timing was compatible with a coordinated head-eye orientating response. (5) On the basis of the directions, and the latencies, of evoked eye movements, the cat frontal oculomotor area could be divided into two subregions, a 'medial' and a 'lateral', (6) The 'medial' area included the mesial wall of the hemisphere with a portion of the lower lip of the cruciate sulcus, and the medial wall of the presylvian sulcus. This area yielded contraversive eye movements with shorter latencies (average 45 msec). (7) The 'lateral' area included primarily the lateral wall of the presylvian sulcus. It yielded predominantly centering eye movements, and ipsiversive movements with longer latencies (65 msec). (8) The functional characteristics of the 'medial' area, as revealed by focal stimulation, resembled those of the monkey frontal eye field.