Anne Martin, Rudiger von der Heydt; Direct Current Polarization of macaque area V4 reversibly affects saccadic reaction times in a visual discrimination task. Journal of Vision 2010;10(7):1314. doi: 10.1167/10.7.1314.
Purpose: Macaque area V4 is important for object identification. Lesions of area V4 affect an animal's ability to select an odd target in an array. Transcortical direct current stimulation (tDCS) is a reversible method that allows bi-directional polarization of cortex. Application of surface anodal current tends to be stimulating, increasing spontaneous firing rates, while surface cathodal current tends to suppress activity. Here we used tDCS to explore the function of area V4. Methods: A monkey was trained to perform a visual discrimination task where he had to select, with a saccade, a distinct target disc from several distracters arranged in a circular array around a fixation spot. At display onset, current pulses of 6mA with Gaussian profiles (sigma=150ms) were applied to the dura using Ag/AgCl electrodes (1mm diameter x 3mm long rod). Trials with surface positive, negative, and zero current were mixed randomly within a block. Results: The results show that application of tDCS above the dura of macaque area V4 affects the saccadic response times reversibly, on the timescale of a single trial. Response times were shorter with cathodal (surface negative) current, and were increased for anodal current. Conclusions: Thus performance in a visual discrimination task can be modulated using direct current polarization of area V4. The trial-by-trial modulation will be a useful tool for studying the function of visual cortical areas.
NIH grant EY02966 and NIH training grant EY07143.