Activity of fixation neurons in the monkey frontal eye field during smooth pursuit eye movements

Abstract

We recorded the activity of fixation neurons in the frontal eye field (FEF) in trained monkeys and analyzed their activity during smooth pursuit eye movements. Fixation neurons were densely located in the area of the FEF in the caudal part of the arcuate gyrus facing the inferior arcuate sulcus where focal electrical stimulation suppressed the generation of saccades and smooth pursuit in bilateral directions at an intensity lower than the threshold for eliciting electrically evoked saccades. Whereas fixation neurons discharged tonically during fixation, they showed a variety of discharge patterns during smooth pursuit, ranging from a decrease in activity to an increase in activity. Of these, more than two-thirds were found to show a reduction in activity during smooth pursuit in the ipsilateral and bilateral directions. The reduction in activity of fixation neurons began at pursuit initiation and continued during pursuit maintenance. When catch-up saccades during the initiation of pursuit were eliminated by a step-ramp target routine, the reduced activity of fixation neurons remained. The reduction in activity during pursuit was not dependent on the activity during fixation without a target. Based on these results, we discuss the role of the FEF at maintaining fixation in relation to various other brain areas. We suggest that fixation neurons in the FEF contribute to the suppression of smooth pursuit. These results suggest that FEF fixation neurons are part of a more generalized visual fixation system through which suppressive control is exerted on smooth pursuit, as well as saccades.

Improvement of Pursuit Eye Movement Alterations after Short Visuo-Attentional Training in ADHD

“…Longer latencies have also been observed during prosaccades [5], as well as an increased number of errors during anti-saccade tasks and frequent intrusive saccades during smooth pursuit in subjects with ADHD when compared to controls [6]. More recently, our group [7] reported an increased number of intrusive saccades during a fixation task, supporting previous evidence of an alteration in cognitive inhibitory mechanisms and a potential dysfunction of the frontal eye field in subjects with ADHD [8]. Remember that all these tasks (saccades and fixations) involved inhibitory control mechanisms that are mediated by the frontal eye field [9].…”

Functional Categories of Visuomotor Neurons in Macaque Frontal Eye Field

“…This under-representation of movement-related neurons seems curious, for these are thought to be large pyramidal neurons in layer 5 (Fries, 1984; Segraves and Goldberg, 1987; Sommer and Wurtz, 2001), which should be easier to isolate. Similarly, fixation neurons are also layer 5 pyramidal cells (Izawa and Suzuki, 2014), but are instead found in the same proportion as in the study by Bruce and Goldberg (1985). Perhaps the linear electrode array failed to sample layer 5 neurons.…”

“…If these neurons do indeed inhibit presaccadic movement neurons, then this could be the origin of the brief reduction of discharge rate characteristic of the movement neuron consensus cluster 9 con . Greater diversity of this category may be found if tested with pursuit eye movements (Izawa and Suzuki, 2014).…”

Microsaccade production during saccade cancelation in a stop-signal task

“…Though monosynaptic connections from FEF to functionally defined OPNs have not yet been identified, fixation neurons in FEF and SC show similar physiological responses (Bizzi, 1968; Hanes et al, 1998; Paré and Hanes, 2003; Izawa et al, 2009; Izawa and Suzuki, 2014). Both movement and fixation neurons in FEF and SC modulate firing rates on canceled trials in the stop-signal task with timing sufficient to play a direct role in initiating and canceling movements (Hanes et al, 1998, Paré & Hanes, 2003, Schall & Godlove, 2012a).…”