Dorsolateral Prefrontal Cortex Prevents Short-latency Saccade and Vergence: a TMS Study

Abstract

This study explores whether vergence eye movements along the median plane can be triggered with short latencies, and the role of the dorsolateral prefrontal cortex (DLPFC) in controlling such movements. We used a gap paradigm and applied transcranial magnetic stimulation (TMS) in 10 humans making saccades or vergence. TMS over the motor cortex had no effect on any eye movement parameter. TMS over DLPFC influenced eye movement initiation but not their metrics. TMS over the right DLPFC accelerated the triggering of saccades bilaterally but did not influence divergence. TMS over the left DLPFC speeded up the triggering of ipsilateral saccades and exacerbated the anticipatory mode of triggering of divergence. For convergence, TMS effects were mild: rightward TMS increased the proportion of short latencies but failed to shorten the group mean latency; leftward TMS influenced triggering in some individuals only. For saccades and convergence under TMS, some subjects showed an emerging population of short latencies in their latency distribution. Horizontal saccadic intrusions (80% of trials) and vertical saccades (recorded in one subject) intruding on vergence were unlikely to assist vergence triggering. We conclude that the prefrontal mechanisms underlying voluntary eye movement control are similar for saccades and vergence although some specificities exist.

Dissociation of the rostral and dorsolateral prefrontal cortex during sequence learning in saccades: a TMS investigation

“…However, further to a number of previous studies which have found stimulation of TMS at the time of target onset causes this reduction in inhibiting reflexive saccades (Coubard and Kapoula, 2005), we have also found that stimulation during a delay between sequences of reflexive saccades can also cause this effect. This is highly possible in our task given the tasks were blocked according to task i.e.…”

Saccades during symmetrical vergence

“…1b) were 161±24 ms for convergence and 160±12 ms for divergence [13]. We now present the characteristics of saccades accompanying vergence.…”

“…Further details concerning TMS methodology and coil positioning can be found in our prior report [13]. The present study specifically details TMS effects on the rate, latency, duration, amplitude and peak velocity of saccades during symmetrical vergence.…”

“…In our prior report [13], we introduced TMS effects on the proportion and latency of saccades during vergence (also reported below). The present section reports new analysis investigating further the influence of TMS on duration and dynamics of saccade during vergence.…”

“…The present data of the first experiment were extracted from a TMS study in which we explored the effects of TMS over the dorsolateral prefrontal cortex (DLPFC) on pure saccade and symmetrical vergence latency in the horizontal plane [13]. For the first time, we showed that prefrontal TMS could elicit short-latency vergence, particularly convergence.…”