Drug application procedures

The opening diameter of the pipettes varied between 1–4 μm and their resistance varied between 10–150 MΩ, with most recordings (> 90%) at 20–80 MΩ⁴², while recording electrode resistance was 0.5–2 MΩ. Hold currents for scopolamine and mecamylamine were usually − 10 nA, in rare occasions (when the pipette resistance was 10–20 MΩ) it was − 40 nA. Pipette electrode combinations were inserted into V1 through the dura on a daily basis without the use of guide tubes. The integrity of the electrode and the pipettes were checked under the microscope before and after the recording sessions, in addition to measurements of the pipette impedance made before and after the recording at each recording site. The details regarding drug concentration, pH and application current were: scopolamine (0.1 M, pH 4.5, median current strength: 40 nA, 25 percentile: 30 nA, 75 percentile: 50 nA), and mecamylamine (0.1 M, pH 4.5, median current strength: 10 nA, 25 percentile: 5 nA, 75 percentile: 10 nA).

Drug application was continuous during blocks of ‘drug applied’. The duration of each block could vary depending on the number of repetitions for each condition that we aimed for, and depending on the number of eye fixation errors that the monkey made. On average drug application for each block was ~ 7–12 min. For the data analysis we removed the first 2 trials of each condition from the data set, as drug effects and recovery usually occur with a slight delay of ~ 30 s. We regularly compensated for the change in current during the ejection condition by increasing the hold current of one of the two pipettes, thereby keeping the overall current identical between the ‘hold’ and ‘eject’ conditions.