Two adult male rhesus monkeys (Macaca mulatta, G and T) participated in this study. All surgical and animal care procedures were conducted in accordance with National Institutes of Health guidelines and were approved by the California Institute of Technology Animal Care and Use Committee. The monkeys were head fixed and trained to reach with the left arm to a touch-sensitive screen (Elo TouchSystems, Menlo

Park, CA) placed in front of an LCD monitor. Eye position was monitored with an infrared eye-tracking camera (ISCAN, Arrington Research). Figure 1A illustrates the behavioral paradigm. At the start of each trial, the animal was required to fixate his eyes on a small red square and to touch a small green square. After a 1 s fixation period, a second green square (the target) was illuminated. The monkey continued to hold the ocular and manual fixations for a variable delay period (1.2–1.5 s) until the initial manual fixation this website ATR inhibitor point was extinguished. This was the signal for the animal to reach to the target location while maintaining visual fixation. If the animal successfully acquired the target within 0.7 s and then held his hand on it for 0.25 s without moving his gaze, he was rewarded with a drop of juice. Behavioral tolerance windows had radii of 4 degrees (eye fixation) and 5 degrees (initial

hand position and target). In the center-out task, the initial ocular and manual fixation points were next to each other in the center of the screen and eight reach targets were spaced evenly around the fixation points at 20 degree eccentricity. In this task, the target was extinguished after 0.4 s and the animal made a reach to a remembered location 0.8–1.1 s later. In the reference frame task (Figure 1B), the initial hand position (H) was at −20, −10, 0, or 10 degrees along a horizontal line (screen-centered coordinates) and the gaze fixation positions (G) varied across the same four positions. The reach target (T) was also at one of four locations (−20, −10, 0, or 10 degrees) on a horizontal line either 16

degrees above or below the fixation positions, whichever would best activate the cell. The 4 gaze fixations, 4 hand fixations, until and 4 target positions combined to give a total of 64 different trial types. In this task, the target remained illuminated throughout the delay period to make the task easier for the monkeys to perform. Previous studies of area 5d show that cells here have little or no direct response to the onset of the visual cue (Cui and Andersen, 2011), so it is unlikely that recorded neural activity during the delay period is due to the ongoing visual stimulation. All reaches were made within the frontal plane formed by the touchscreen, which was at a distance of 30 cm (monkey G) or 26 cm (monkey T) from the eyes. In both animals, a recording chamber was implanted over the right posterior parietal cortex under isoflurane anesthesia.