Functional Distinction Between Visuomovement and Movement Neurons in Macaque Frontal Eye Field During Saccade Countermanding

Abstract

In the previous studies on the neural control of saccade initiation using the countermanding paradigm, movement and visuomovement neurons in the frontal eye field were grouped as movement-related neurons. The activity of both types of neurons was modulated when a saccade was inhibited in response to a stop signal, and this modulation occurred early enough to contribute to the control of the saccade initiation. We now report a functional difference between these two classes of neurons when saccades are produced. Movement neurons exhibited a progressive accumulation of discharge rate following target presentation that triggered a saccade when it reached a threshold. When saccades were inhibited with lower probability in response to a stop signal appearing at longer delays, this accumulating activity was interrupted at levels progressively closer to the threshold. In contrast, visuomovement neurons exhibited a maintained elevated discharge rate following target presentation that was followed by a further enhancement immediately before the saccade initiation. When saccades were inhibited in response to a stop signal, the late enhancement was absent and the maintained activity decayed regardless of stop-signal delay. These results demonstrate that the activity of movement neurons realizes the progressive commitment to the saccade initiation modeled by the activation of the go unit in computational models of countermanding performance. The lack of correspondence of the activity of visuomovement neurons with any elements of these models indicates that visuomovement neurons perform a function other than the saccade preparation such as a corollary discharge to update visual processing.

Separate evaluation of target facilitation and distractor suppression in the activity of macaque lateral intraparietal neurons during visual search

“…We identified the time point at which a single LIP neuron discriminated the target from distractors in terms of its activity (target discrimination time), using a modified version of the analytical method described in previous studies (e.g., Murthy et al 2009;Ray et al 2009). Using receiver operating characteristic (ROC) analysis, we first computed the area under the curve (AUC) between the distributions of the trial-based spike density functions derived from the target-and distractor-related activities.…”

Understanding How the Brain Changes Its Mind: Microstimulation in the Macaque Frontal Eye Field Reveals How Saccade Plans Are Changed

“…Compensation functions (see Fig. 1C) were fit by a cumulative Weibull function as follows Ray et al, 2009):…”

Response Inhibition

“…Activity of these fixation neurons turns back on at 200 ms after the onset of the stop signal. Recording from the FEF of monkeys showed reduction of movement-related activities prior to the end of the stop signal reaction time (SSRT) (Ray et al, 2009). Together, these findings are indicative of an interactive process in the control of saccade initiation (Schall & Godlove, 2012).…”