Katherine M. Armstrong, Tirin Moore; Effects of frontal eye field microstimulation on the discriminability of visual responses in area V4. Journal of Vision 2006;6(6):748. doi: 10.1167/6.6.748.
The source of the perceptual and neurophysiological enhancements observed during selective attention is largely unknown. Recent work has implicated the frontal eye field (FEF), an oculomotor area in the frontal lobe, in the modulation of visual responses in extrastriate cortex. Subthreshold FEF microstimulation enhances responses of retinotopically overlapping V4 neurons in passively viewing monkeys. This effect depends on the stimulus presented to the receptive field (RF): more enhancement is observed for effective than for ineffective stimuli, consistent with the effect of voluntary attention on visual responses. In this study, we examined whether the graded enhancement following microstimulation actually improves the ability of V4 neurons to discriminate different RF stimuli. We used signal detection theory to quantify how well V4 responses could distinguish between two oriented-bar stimuli. Receiver-operator-characteristic (ROC) curves, computed for each neuron's responses, provided a measure by which to examine the impact of FEF stimulation on stimulus discriminability. Several hundred milliseconds after visual stimulus onset, response adaptation had markedly reduced the discriminability of V4 responses to different RF stimuli. However, we found that microstimulation at this point in the trial could transiently increase the area of ROC curves, and thus improve the ability of V4 neurons to discriminate visual stimuli. This suggests that oculomotor signals can improve the stimulus discriminability of neural responses in visual cortex that encode impending saccade targets, or covertly attended stimuli.
NIH EY014924, Pew, the Sloan Foundation, and a HHMI predoctoral fellowship to KMA.