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Jitendra Sharma, Valentin Dragoi, Earl K. MIller, Mriganka Sur; Modulation of responses in mokey V1 by an eye position task. Journal of Vision 2002;2(7):161. doi: 10.1167/2.7.161.
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The integration of retinal and extra-retinal, including oculomotor inputs to the brain is essential for localization of stimuli in space, dynamic stabilization of receptive fields, and for selective attention to a particular object or location to enhance perceptual sensitivity. Neurons in primary visual cortex (V1) are modulated by direction of gaze. It remains unknown whether V1 response can change if retinal inputs and gaze are held constant, depending on task demand. Such a change would define top-down influences reflecting internal state of the animal.
We examined responses to oriented gratings in awake monkey V1 while the animal engaged in performing a fixation task. The fixation spot appeared at three different locations in horizontal plane. The animal was rewarded for maintaining fixation for a period of 1–1.5 sec. with a drop of juice. Single neuron responses to sinusoidal gratings (eight orientations, 2 directions, presented in 10×10 deg. window covering neurons' receptive field) were recorded. Two task conditions were used. In one (randomized trials), trials were presented in a pseudo-random fashion in any of the 3 gaze directions, while in the other (grouped trials) the fixation spot appeared in same gaze direction for 10–15 trials. Our results show that in randomized trials 20% neurons were significantly modulated by the change in gaze direction whereas when trials were grouped, as many as 68% neurons showed gain modulation.
Our data clearly shows task dependent changes in gaze modulation, reflecting top-down influences, such as focal verses distributed attention.
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