Reversible inactivation of macaque frontal eye field

Abstract

The macaque frontal eye field (FEF) is involved in the generation of saccadic eye movements and fixations. To better understand the role of the FEF, we reversibly inactivated a portion of it while a monkey made saccades and fixations in response to visual stimuli. Lidocaine was infused into a FEF and neural inactivation was monitored with a nearby microelectrode. We used two saccadic tasks. In the delay task, a target was presented and then extinguished, but the monkey was not allowed to make a saccade to its location until a cue to move was given. In the step task, the monkey was allowed to look at a target as soon as it appeared. During FEF inactivation, monkeys were severely impaired at making saccades to locations of extinguished contralateral targets in the delay task. They were similarly impaired at making saccades to locations of contralateral targets in the step task if the target was flashed for ≤100 ms, such that it was gone before the saccade was initiated. Deficits included increases in saccadic latency, increases in saccadic error, and increases in the frequency of trials in which a saccade was not made. We varied the initial fixation location and found that the impairment specifically affected contraversive saccades rather than affecting all saccades made into head-centered contralateral space. Monkeys were impaired only slightly at making saccades to contralateral targets in the step task if the target duration was 1000 ms, such that the target was present during the saccade: latency increased, but increases in saccadic error were mild and increases in the frequency of trials in which a saccade was not made were insignificant. During FEF inactivation there usually was a direct correlation between the latency and the error of saccades made in response to contralateral targets. In the delay task, FEF inactivation increased the frequency of making premature saccades to ipsilateral targets. FEF inactivation had inconsistent and mild effects on saccadic peak velocity. FEF inactivation caused impairments in the ability to fixate lights steadily in contralateral space. FEF inactivation always caused an ipsiversive deviation of the eyes in darkness. In summary, our results suggest that the FEF plays major roles in (1) generating contraversive saccades to locations of extinguished or flashed targets, (2) maintaining contralateral fixations, and (3) suppressing inappropriate ipsiversive saccades.

Reversible inactivation of macaque dorsomedial frontal cortex: effects on saccades and fixations

“…We previously have described the infusion methods (Sommer and Tehovnik 1997) and quantified the time course and spread of cortical inactivation subsequent to lidocaine infusion (Tehovnik and Sommer 1997a). In summary, a 30-gauge needle was attached to a stainless-steel cannula that was connected to a 100-µl Hamilton syringe using PE 50 tubing.…”

“…We used the two monkeys (Macaca mulatta) that had been used in our FEF inactivation study (Sommer and Tehovnik 1997). For monkey I, we alternated between inactivating the DMFC and the FEF.…”

“…For monkey L, we performed the DMFC inactivation experiments after the FEF experiments. Surgical details were described previously (Sommer and Tehovnik 1997). A monkey was implanted with a scleral search coil for recording eye position (Robinson 1963;Judge et al 1980), a stainless steel post for restraining the head, and chambers for accessing the brain.…”

“…Our second goal was to directly compare the functions of the DMFC with those of the FEF. We therefore inactivated the DMFC using the same methods and the same monkeys as in our previous study of FEF inactivation (Sommer and Tehovnik 1997).…”

“…We used the same behavioral tasks as in our FEF study (Sommer and Tehovnik 1997), which showed that FEF inactivation causes severe impairments in some of these tasks, e.g., it disrupts single contraversive saccades made to briefly flashed targets. In the present study, however, we found that DMFC inactivation had little effect on behavior in these tasks.…”