How the frontal eye field can impose a saccade goal on superior colliculus neurons

Abstract

Saccades were electrically evoked from the frontal eye field (FEF) of two trained monkeys while saccade-cells were recorded from the intermediate layers of the superior colliculus (SC). We found that FEF microstimulation, eliciting saccades of a given vector, excited SC saccade-cells encoding the same vector and inhibited all others. Such a mechanism can prevent competing commands from arising simultaneously in different structures.

Our eyes deviate away from a location where a distractor is expected to appear

“…Responses in the FEF are responsive to task demands which are shown for example by different responses to targets and distractors (Bichot and Schall 2002). In visual search, the FEF have been shown to select one population of activity as the target and inhibit the distractor location (Schlag-Rey et al 1992).…”

Colliding saccades evoked by frontal eye field stimulation: artifact or evidence for an oculomotor compensatory mechanism underlying double-step saccades?

“…In this case, where the transformation occurs within FEF, we would expect to see the results of this transformation in FEF output target sites including SC. This is not the case, however, as FEF stimulation in the collision paradigm has been shown to produce activity in SC that corresponds to the site of FEF stimulation with no compensation, indicating that in these circumstances the compensation takes place downstream in a structure that receives FEF input (Schlag-Rey et al 1992). On the other hand, if the behavioral compensation were due only to the proposed subcortical mechanism, then how could one explain the observations of compensation in cortical oculomotor structures?…”

“…There is evidence that the transformation does not occur in FEF itself, but downstream from FEF. Schlag-Rey et al (1992) recorded from SC saccade-related cells during stimulation in FEF that produced colliding saccades. Activity recorded in the SC cells corresponded to an encoding of the fixed vector as stimulated in FEF, and not to the evoked movement.…”

“…Thus the system attempts to compensate for the eye movement that occurred between the target presentation and the corresponding saccade by subtracting that movement. Note that in cases where the signals issuing from SC and from FEF/C differ due to this shift, we assume that the cortical command will dominate, based on the observation that in colliding saccades evoked by FEF stimulation, the saccade coded by SC did not correspond to the saccade produced (Schlag-Rey et al 1992). We can consider that it is indeed a total override, rather than a summation, since a summation would never allow saccade reversals, which are easily obtained in FEF collisions (Dassonville et al 1992b).…”

The control of saccade trajectories: Direction of curvature depends on prior knowledge of target location and saccade latency

“…Instead, a different, nonlocal kind of inhibition is required, based on a top-down projection from other structures. For example, the frontal eye fields (FEFs) are known to exert an inhibitory influence on the colliculus (Schlag-Rey, Schlag, & Dassonville, 1992) and could further inhibit distractor-related activity below baseline, resulting in the deviation of saccades away from distractors.…”