Perceptual bias induced by optical stimulation in the macaque frontal eye field

We studied differences between optical and electrical micro-stimulation (MS) in the macaque frontal eye field (FEF) using single unit recordings, behavioral essay and fMRI. The frontal eye field serves as ideal test bed since it has been thoroughly characterized with electrical stimulation and because a behavioral effect (i.e. saccade) is easily induced by electrical MS. Three different constructs (AAV5-hSyn-eNpHR3.0, AAV5-hSyn-ChR2, AAV5-CAG-Arch) were injected to three FEF sites in two monkeys and robust firing rate modulations were observed upon light delivery. Although activity modulation was observed as far as 2mm away from the optical stimulation site, no significant voxel activation was found during combined fMRI and optical stimulation. High current electrical MS reliably induced saccades. Low current electrical MS combined with optical stimulation increased the probability of eliciting a saccade, suggesting optical stimulation may be similar to a low current electrical MS, known to induce an attentional bias. To test the possible effects of optical stimulation on attention monkeys were trained on a delayed memory saccade task. We observed significant changes in performance during optical stimulation trials, such as an increase in incorrect and missed trials, suggesting monkeys failed to perceive the instructed cue signal in the periphery.