The stimulus changes were small changes in the grating pattern, with the stripes

undergoing a gentle bend (Figure 1E). During the bend, the outer ends of the grating stripes lagged increasingly behind the center of the stripes, until the lag reached 0.1° at 75 ms after the start of the bend. Over the course of another 75 ms, the stripes straightened again. We used this shape-change detection task, because previous studies on gamma-band activity in monkey area V4 had found larger attention effects for a shape-tracking task (Taylor et al., 2005) than a color-change detection task (Fries et al., 2001, 2008). On 10% of the trials, only one of the two stimuli was presented, randomly at one or the other position and tinted yellow or blue. In these trials, the fixation point always assumed the color of this one grating, the change time was determined according to the same hazard rate, VX-770 chemical structure and if the monkey released within 0.15–0.5 s thereafter, a reward was given. Several sessions (either Cabozantinib purchase separate or after attention-task sessions) were devoted to the mapping of receptive fields, using 60 patches of moving grating, as illustrated in Figure S1C. Receptive field positions

were stable across recording sessions (Figure S1D). Neuronal recordings were made from two left hemispheres in two monkeys through a micromachined 252-channel electrocorticogram-electrode array implanted subdurally (Rubehn et al., 2009). Briefly, a 6.5 × 4 cm craniotomy over the left hemisphere in each monkey was performed under aseptic conditions with isoflurane anesthesia. The dura was opened and the ECoG was placed directly Astemizole onto the brain under visual control. Several high-resolution photos were taken before and after placement of the ECoG for later coregistration of ECoG signals with brain regions. After ECoG implantation, both the bone and the dural flap were placed back and secured in place. After a recovery period of approximately 3 weeks, we started with neuronal recordings. Signals obtained

from the 252 electrode grid were amplified 20 times by eight Plexon headstage amplifiers, then low-pass filtered at 8 kHz and digitized at 32 kHz by a Neuralynx Digital Lynx system. LFP signals were obtained by low-pass filtering at 200 Hz and downsampling to 1 kHz. Powerline artifacts were removed by digital notch filtering. The actual spectral data analysis included spectral smoothing that rendered the original notch invisible. All analyses were done in MATLAB (MathWorks) and using FieldTrip (Oostenveld et al., 2011) (http://fieldtrip.fcdonders.nl). For the analysis of the data recorded during the attention task, we used the time period from 0.3 s after cue onset (the change in the fixation point color) until the first change in one of the stimuli. For each trial, this period was cut into nonoverlapping 0.5 s data epochs, discarding remaining time at the end of the period that was less than 0.5 s long.