Suppression of Visually and Memory-Guided Saccades Induced by Electrical Stimulation of the Monkey Frontal Eye Field. I. Suppression of Ipsilateral Saccades

Abstract

When a saccade occurs to an interesting object, visual fixation holds its image on the fovea and suppresses saccades to other objects. Electrical stimulation of the frontal eye field (FEF) has been reported to elicit saccades, and recently also to suppress saccades. This study was performed to characterize properties of the suppression of visually guided (Vsacs) and memory-guided saccades (Msacs) induced by electrical stimulation of the FEF in trained monkeys. For any given stimulation site, we determined the threshold for electrically evoked saccades (Esacs) at < or =50 microA and then examined suppressive effects of stimulation at the same site on Vsacs and Msacs. FEF stimulation suppressed the initiation of both Vsacs and Msacs during and about 50 ms after stimulation at stimulus intensities lower than those for eliciting Esacs, but did not affect the vector of these saccades. Suppression occurred for ipsiversive but not contraversive saccades, and more strongly for saccades with larger amplitudes and those with initial eye positions shifted more in the saccadic direction. The most effective stimulation timing for suppression was about 50 ms before saccade onset, which suggests that suppression occurred in the efferent pathway for generating Vsacs at the premotor rather than the motoneuronal level, most probably in the superior colliculus and/or the paramedian pontine reticular formation. Suppression sites of ipsilateral saccades were distributed over the classical FEF where saccade-related movement neurons were observed. The results suggest that the FEF may play roles in not only generating contraversive saccades but also maintaining visual fixation by suppressing ipsiversive saccades.

Suppression of Visually and Memory-Guided Saccades Induced by Electrical Stimulation of the Monkey Frontal Eye Field. II. Suppression of Bilateral Saccades

“…Stimulation of the most rostral part of the SC suppressed saccades in bilateral directions, with predominant suppression of ipsilateral saccades (Munoz and Wurtz 1993b;Paré and Guitton 1994), and suppressed both Vsacs and Msacs (Munoz and Wurtz 1993b). Burman and Bruce (1997) reported that stimulation of the FEF mainly suppressed contraversive saccades and effectively suppressed Msacs but not Vsacs, whereas our previous study showed that FEF stimulation suppressed the initiation of ipsiversive saccades of both Vsacs and Msacs at low thresholds (Izawa et al 2004). Although the preceding discrepancies have not yet been resolved, these suppressive effects of FEF stimulation on the generation of saccades may contribute to maintaining fixation on a target of interest by preventing saccades to other targets in the visual field.…”

“…Experiments were performed in two male Japanese monkeys (Macaca fuscata) that were also used in the preceding article (Izawa et al 2004). Monkeys were prepared for the experiments using the same procedures and the same series of fixation, visually guided, and memory-guided saccade tasks described in the preceding article (Izawa et al 2004).…”

“…Monkeys were prepared for the experiments using the same procedures and the same series of fixation, visually guided, and memory-guided saccade tasks described in the preceding article (Izawa et al 2004).…”

“…As reported in the previous article (Izawa et al 2004), we systematically examined the effects of stimulation of the FEF and its vicinity in the prearcuate gyrus at a track interval of 500 m and at depth intervals of 200 or 400 m. At individual stimulation sites, we first determined thresholds for eliciting Esacs by microstimulation and identified a site as being within the classical FEF when stimulation elicited Esacs at Յ50 A . In this experiment, we examined the effects of stimulation at the same sites on Vsacs and Msacs at Յ80 A even though electrical stimulation did not evoke Esacs.…”

“…To understand the nature of FEF suppression, we systematically examined the suppressive effects of electrical stimulation of the FEF on saccades in monkeys and reported the unilateral suppression of ipsiversive saccades on FEF stimulation in the previous report (Izawa et al 2004). Such suppression sites for ipsiversive saccades were distributed widely in the FEF where electrical stimulation could induce saccades at Յ50 A.…”