The caudal fastigial nucleus and the steering of saccades toward a moving visual target

Abstract

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. NEW & NOTEWORTHY Unilateral inactivation of the caudal fastigial nucleus impairs the accuracy of saccades toward a moving target. Like saccades toward a static target, interceptive saccades are hypometric when directed toward the contralesional side and hypermetric when they are ipsilesional. The dysmetria depends on target velocity, but the use of accelerating or decelerating targets reveals that velocity is not the crucial parameter. We extend the bilateral fastigial control of saccades and fixation to the production of interceptive saccades.

Dynamic combination of position and motion information when tracking moving targets

“…Another crucial area might be the caudal fastigial nuclei (CFN). Lesions to the CFN impair saccades and pursuit made to moving targets (Bourrelly et al, 2018a(Bourrelly et al, , 2018b. Thus, the impaired motion processing in MT for isoluminant peripheral targets could be the origin for our behavioral results.…”

“…Similarly, the window of integration of information for the initial interceptive saccade might be earlier than for the following pursuit eye movement. Along these lines, we hypothesize that Bourrelly et al (2018a) observed common lesion effects due to a shared signal, but did not find trial-by-trial correlations because the crucial intervals for the relevant signals for saccade and pursuit execution differ. Thus, we propose that the pathways for saccades and pursuit share a continuous target motion signal (or imbalance), but sequential eye movements can differ due to the temporal dynamics of their readout.…”

Neurophysiology of visually guided eye movements: critical review and alternative viewpoint

“…Contrary to the claim that "in [their] programming [...], target motion is used to predict the future target position so as to assure a spatial lead of the gaze at the saccade end, instead of attempting a precise capture of the target" (Klam et al 2001; see also Berthoz 2012), most behavioral studies show that the saccades are such that they do not direct gaze toward a location where the target will be in the future. They direct gaze either toward its current location or toward a location lagging behind (Barmack 1970;Bourrelly et al 2016Bourrelly et al , 2018aFleuriet et al, 2011;Fuchs 1967aFuchs , 1967bKeller and Johnsen 1990;Robinson 1965). The saccades do not orient the foveae toward a location where gaze would wait for the target (like the traveler waits for a bus) to enter within the foveal field and initiate the pursuit.…”

Spatial and temporal adaptation of predictive saccades based on motion inference

“…When directing eyes immediately to a moving object, the brain must adjust motor outputs by computing the future target location at the time of saccade termination. Previous studies suggest a role for the brainstem, the cerebellum and the frontal cortex in this behavior [54][55][56][57][58] . Unlike such an immediate adjustment of interceptive saccades, our behavioral paradigm required temporal storage of target information as well as the adjustment of movement timing, which may recruit additional neuronal processes.…”