Spatial organization of visual messages of the rabbit's cerebellar flocculus. I. Typology of inferior olive neurons of the dorsal cap of Kooy.

1. Single-unit responses to large-field visual stimuli were recorded extracellularly from neurons in the dorsal cap of Kooy of the inferior olive in anesthetized, paralyzed rabbits. The visually modulated neurons in the dorsal cap responded optimally to slow rotation of random dot stimuli, which were produced using handheld patterns or a planetarium projector. 2. Neurons had either monocular or binocular receptive fields. For binocular receptive field neurons, monocular stimulation of one eye, called the dominant eye, elicited greater modulation than did stimulation of the other eye. Rotation about a particular axis, called the preferred axis, produced both maximal excitation and inhibition. On the basis of differences in preferred axis orientation and in eye dominance, three neuron classes called Vertical Axis, Anterior (45 degrees) Axis, and Posterior (135 degrees) Axis were distinguished. 3. Vertical Axis neurons were modulated exclusively from the eye contralateral to the inferior olive recording site. This cell type responded strongly to large-field visual stimuli rotating about the vertical axis. Excitation resulted from movement in the temporal to nasal direction, and inhibition occurred during movement in the nasal to temporal direction. 4. Two subclasses of Anterior (45 degrees) Axis neurons were distinguished according to whether the receptive field was monocular or binocular. For both subclasses, the dominant eye was ipsilateral. The receptive field organization of the dominant eye was bipartite as described in the previous paper (51) for neurons in the midbrain visual tegmental relay zone. Anterior (45 degrees) Axis neurons were maximally excited when the stimulus pattern moved upward and posterior above the horizon in the anterior quadrant of the ipsilateral visual field, from 0 degrees (nose) to approximately 45 degrees azimuth. From 45 to 180 degrees azimuth (occiput) and above the horizon, these neurons were excited by downward and posterior movement. Inhibition occurred with oppositely directed movements. For rotating stimuli presented to the dominant eye, this class of neurons responded best to rotation of the visual world about an axis oriented near the horizontal plane and approximately 45 degrees azimuth. 5. The receptive field of Posterior (135 degrees) Axis neurons was always binocular, with the dominant eye contralateral. For the contralateral receptive field, from 0 degree (nose) to 135 degrees azimuth and above the horizon, excitation occurred during upward and posterior movement.(ABSTRACT TRUNCATED AT 400 WORDS)