Role of the cerebellar floccular lobe and vermis in vertical smooth pursuit eye movement

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To understand how the floccular lobe is involved in vertical smooth pursuit and vestibulo-ocular reflex (VOR), we examined simple-spike activity of 58 vertical Purkinje (P-) cells. Vertical gaze velocity (VG) P-cells constituted only a minority of vertical P-cells (19%). Other P-cells that responded during pitch VOR suppression were classified as eye and head velocity (V E/H) P-cells (48%), regardless of the synergy of their response direction during pursuit and VOR suppression. Vertical P-cells that did not respond during pitch VOR suppression but responded during rotation in vertical planes other than pitch were classified as off-pitch V E/H P-cells (33%). The mean eye-velocity and eye-position sensitivities of the 3 types of vertical P-cells were similar. Maximal vestibular activation directions (MADs) were examined during VOR suppression by applying vertical whole body rotation with the monkeys oriented in different vertical planes. The MADs for VGP- and V E/H P-cells with eye and … More vestibular sensitivity in the same direction were distributed near the pitch plane, suggesting convergence of bilateral anterior canal inputs. In contrast, MADs of off-pitch V E/ HP-cells and V E/H P-cells with oppositely directed eye and vestibular sensitivity were shifted towards the roll plane, suggesting convergence of anterior and posterior canal inputs of the same side. Unlike horizontal GP-cells, the modulation of many V G and V E/H P-cells when the target was fixed in space (pitch VOR x1) was not well predicted by the linear addition of their modulations during vertical pursuit and pitch VOR suppression. These results indicate that the populations of vertical and horizontal eye-movement P-cells in the floccular lobe have markedly different discharge properties. Recordings in the cerebellar vermis using identical paradigms revealed many G P-cells with oblique preferred directions. These results suggest that these two structures are involved in different kinds of processing of vestibular-oculomotor interactions. Less