Climbing fiber responses of Purkinje cells to retinal image movement in cat cerebellar flocculus.

1. The complex spike (CS) of the floccular Purkinje cell has been reported to be driven by retinal image movement in the rabbit, the rat, and the monkey, but not yet in the cat, in which the floccular neuronal network is well known. We recorded the CS activity together with concomitant simple spike (SS) activity of the floccular Purkinje cells that responded to large-field visual pattern movement in the anesthetized cat. 2. On the basis of the direction selectivity we divided the cells into two major types: the horizontal type that preferred horizontal stimuli and the vertical type that preferred vertical stimuli. The CS activity of the horizontal-type cell increased during stimuli directed contralaterally to the recording site and decreased during ipsilaterally directed stimuli, whereas that of the vertical-type cell increased during upward stimuli and decreased during downward stimuli. 3. In both types the CS response was larger at lower-velocity stimuli and the response was well maintained at higher-velocity stimuli < or = 180 degrees/s tested. The mean response decline was only 50% at stimulus velocities 90-150 degrees/s compared with the response amplitude at 2 degrees/s stimulus velocity. 4. The majority of the horizontal-type cells were modulated by the stimuli presented to either eye and the dominant eye was ipsilateral to the recording site. The majority of the vertical-type cells were also modulated by the stimuli presented to either eye without obvious differences between two eyes. 5. In both types the receptive field of the ipsilateral eye always included the area centralis and extended widely on both visual hemifields. The receptive field of the contralateral eye also included the area centralis and was usually restricted within the ipsilateral visual hemifield. The stimuli of small visual field (15 degrees x 15 degrees) projecting to the area centralis evoked especially large responses (70% of the full-screen response). 6. The CS and SS responses were reciprocal to each other, that is, when the CS firing increased the SS firing decreased and vice versa. 7. These CS responses are well suited for the direction detection of large-field retinal image motion at a wide velocity range. In light of the present unitary spike data together with the anatomic and eye movement data reported previously, we conclude that the cat flocculus is responsible for reduction of the large-field retinal image motion by producing eye movement in the same direction with the visual motion.