Figure 1.

Highly schematic model of the brainstem and cerebellar components of the saccadic system. Signals from the SC reach the brainstem BG for horizontal saccades through a relatively direct pathway and also via a side loop through the oculomotor cerebellum (shaded), which consists of the OMV (lobules VIc and VII) and the CFN to which it projects. In addition to a mossy fiber (mf) input from the SC delivered via the nucleus reticularis tegmenti pontis (NRTP), the OMV receives climbing fiber (cf) signals exclusively from the inferior olive (IO), which has been proposed to relay an error signal. The mossy fiber input results in the high rate simple spike discharge (inset, gray), whereas the climbing fiber input produces the complex spike (black), which occurs much less frequently. The P-cell in the inset shows a burst of simple spikes for the 5° saccade shown in the top trace. MN, Horizontal motoneurons, EOM; extraocular muscles.