Direction selective climbing fiber responses to horizontal and vertical optokinetic stimuli in the cat cerebellar flocculus.

In ketamine anesthetized cats, complex spike (CS) responses to movement of a large-field visual surround (optokinetic stimulus) were recorded in the cerebellar flocculus. Two types of Purkinje cells were found. One type showed increased CS activity to optokinetic stimuli directed contralaterally to the recording site and decreased activity to stimuli directed ipsilaterally. The modulation occurred in both monocular (responses to the stimuli for only the ipsilateral eye) and binocular forms (dominant eye, ipsilateral). The other type of cell showed increased CS activity during upward optokinetic stimuli and decreased activity during downward stimuli. The responses occurred only in the binocular form. The dominant eye was either ipsilateral or contralateral with respect to the recording site. Thus, there are two types of Purkinje cells in the cat flocculus: horizontal type cell showing CS modulation during horizontal optokinetic stimuli, and vertical type cell showing CS modulation during vertical optokinetic stimuli.