We recorded extracellular neuronal activity from three hemispheres in three male macaque monkeys (Macaca mulatta), whilst applying ACh, scopolamine or mecamylamine iontophoretically on selected trials. Animals were implanted with a custom made head-holding device and recording chambers made of Tecapeek GF for compatibility in functional magnetic resonance imaging settings. Surgical procedures were performed under aseptic conditions and general anaesthesia. Experiments and surgeries were performed in accordance with the European Communities Council Directive 1986 (86/609/EEC), the National Institutes of Health (Guidelines for Care and Use of Animals for Experimental Procedures), the Society for Neurosciences Policies on the Use of Animals and Humans in Neuroscience Research, and the UK Animals Scientific Procedures Act.
The monkey’s task was to detect a small change in luminance at a cued (attended) location, while ignoring a change that occurred at a non-cued location and fixating a central fixation spot throughout the trial. After a fixation-only period, two identical stimuli were presented (test stimuli): one centred on the receptive field and the other at the same eccentricity in the opposite hemi-field. After 500–800 ms (randomized in 1 ms steps) a patch appeared at the centre of one of the bars. If presented in the cued location the monkey had to release the touch bar within 500 ms to receive a juice reward. If presented in the un-cued location the monkey had to continue to hold the touch bar and maintain fixation until target appearance. This occurred 1,000–1,300 ms (randomized in 1 ms steps) after the distracter appeared. Thus, we recorded activity when animals attended to the receptive field of the neuron under study and when they attended away from it. We then compared activity levels for these attentional conditions with and without drug application.
For all further information about the paradigm, the neuronal recordings, iontophoresis and data analysis, see Supplementary Methods.