Neural correlates of divided orienting in frontal eye field in a search-step task

Abstract

We developed a search-step paradigm that combines the classic double-step task with a visual search task to investigate the dynamics of visual selection and saccade preparation in the macaque frontal eye field (FEF). Monkeys were trained to shift gaze to an oddball target among a circular array of distractors. Infrequently, the target and one distractor would swap locations after some variable delay. This delay was adjusted on-line so that half of the search-step trials resulted in a compensated saccade (gaze shift to the final target location which was reinforced) and half were non-compensated (gaze shift to the original target location which was not reinforced). Visual neurons in FEF signal the location of the target whether or not gaze shifts to it (Murthy et al. 2001 J Neurophysiol 86:2634). The current report is based on a neuron-antineuron analysis of activity when the target stepped into or out of each neuron's response field. Two observations were made in compensated target-step trials. First, visual neurons commonly exhibited a transitory period of coactivation during which two separate locations in the visual field were represented simultaneously. Second, the movement neurons producing the compensated saccade commonly became active while the movement neurons producing the noncompensated saccade were still active. These observations are consistent with the hypothesis that when reacting to rapidly changing scenes attention can be allocated to separate locations and more than one saccade can be partially prepared.

Footnotes

 Supported by R01 EY08890, P30 EY08126 and the McKnight Endowment Fund for Neuroscience