The caudal fastigial nucleus and the steering of saccades toward a moving visual target
Résumé
The caudal fastigial nuclei (cFN) are the output nuclei by which the medio-posterior cerebellum influences the production of visual saccades. We investigated in two head-restrained monkeys their contribution to the generation of interceptive saccades toward a target moving centrifugally by analyzing the consequences of a unilateral inactivation (10 injection sessions). We describe here the effects on saccades made toward a centrifugal target that moved along the horizontal meridian with a constant (10, 20, or 40°/s), increasing (from 0 to 40°/s over 600 ms), or decreasing (from 40 to 0°/s over 600 ms) speed. After muscimol injection, the monkeys were unable to foveate the current location of the moving target. The horizontal amplitude of interceptive saccades was reduced during contralesional target motions and hypermetric during ipsilesional ones. For both contralesional and ipsilesional saccades, the magnitude of dysmetria increased with target speed. However, the use of accelerating and decelerating targets revealed that the dependence of dysmetria upon target velocity was not due to the current velocity but to the required amplitude of saccade. We discuss these results in the framework of two hypotheses, the so-called “dual drive” and “bilateral” hypotheses.