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Behrad Noudoost, Tirin Moore; Effects of frontal eye field inactivation on visual responses of area V4 neurons. Journal of Vision 2008;8(6):392. doi: https://doi.org/10.1167/8.6.392.
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Recent work has shown that electrical microstimulation of the frontal eye field (FEF) alters the visually-driven responses of neurons within visual cortex. Although these observations suggest that FEF neurons exert a top-down influence on visual cortical representations, it has not yet been demonstrated. We investigated the effects of reversible FEF inactivation on the visual responses of area V4 neurons in alert monkeys. Using a custom-designed recording/microstimulation/microinfusion cannula, we delivered small volumes (100 - 800 nL) of drugs to select sites within the FEF. At different FEF sites, we first determined the location to which saccades could be evoked by microstimulation (current [[lt]]50 uA). As in previous microstimulation studies, we then located FEF sites at which the evoked saccade shifted the monkey's gaze to a location within the receptive field (RF) of a V4 neuron being recording from simultaneously. Next, we infused GABA agonists (muscimol or GABA) into the FEF site and the measured the behavioral effects of the inactivation using a memory-guided saccade task. In most cases, within ∼45 minutes, the monkey showed a spatially-selective deficit on the task, and at the location of the V4 RF. We then studied the visual responses of V4 neurons to stimuli presented within the FEF scotoma using both passive fixation and saccade tasks. In the saccade task, the monkey made visually-guided saccades to RF stimuli or to targets presented at non-RF locations after a delay. We could therefore measure the effects of FEF inactivation both on the visual guidance of saccades to RF stimuli and on the pre-saccadic visual activity of V4 neurons. Thus far, we have found that inactivation of the FEF not only increases the scatter of visually-guided saccades to visual targets in the scotoma, but that it alters the visually-selective responses of V4 neurons with RFs at the same location.
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