Figure 1. Behavioral protocol, performance, and recording site. a, After grasping a lever and holding fixation for 500 ms, a sample stimulus of varying contrast was flashed for 500 ms in 50% of the trials (top branch), and no stimulus was shown in the remaining 50% (bottom branch). After a delay of 2000 ms, one of four target stimuli was shown and, depending on whether or not a sample stimulus was presented, either instructed the monkey to release the bar or to withhold a response. b, Instructed response rules (left column) with respect to stimulus condition (middle and right column) by the respective rule cues. c, Psychometric detection curves for Monkey Q (top, 70 sessions) and Monkey Z (bottom, 59 sessions) subdivided in control (Cntl), Bic, and MK trials. d, Lateral view of a macaque monkey brain. Circled area represents the area of extracellular recording and iontophoresis targeting GABA(A) and NMDA receptors at the principal sulcus.