[The neuronal reactions of the nucleus isthmi area in the frog rana temporaria to visual stimuli].

Studies have been made on the neuronal reactions in the isthmic nucleus area of the frog to visual moving stimuli and to changes in total illumination. Visually activated neurons of this area are characterized by large receptive fields (located only in the visual field of contralateral eye), intensive reactions to diffuse illumination, high sensitivity to moving contrast targets (especially large ones) and evident adaptation. Approximately 23% of the neurons exhibited directional sensitivity, mainly to targets moving in temporo-nasal direction. The area of blindness (scotoma) was revealed in the antero-superior part of the receptive fields after partial visual deafferentation of the tectum produced by coagulation of the medial marginal optic tract. Preservation of specific channels of visual information in the retino-tecto-isthmic pathway is discussed.