Figure 1.

Task paradigm and recording penetrations. A, Sketch of the handle (left) and photographs of a monkey performing a precision grip (middle) and a power grip (right). In the drawing, the red dotted line indicates a light barrier for detecting power grips, and the red oval indicates a touch sensor in a groove for sensing precision grips (a second sensor is located on the opposite side of the handle). The handle was presented in five different orientations. B, Delayed grasping task. Trials were divided into four epochs: fixation, cue, planning, and movement. Monkeys initiated trials by placing both hands on rest sensors and fixating a red LED in the dark. After a variable delay (fixation, 700–1100 ms), the handle was illuminated for 600 ms (cue), revealing its orientation. At the same time, a second colored LED (“context cue”) was illuminated, which instructed the animal about the required grip type (power or precision). After a variable delay (planning, 700–1100 ms), the dimming of the fixation light served as the go signal to initiate movement execution. All trial conditions were randomly interleaved. C, Cue separation task. Modified task from B, with the cues for grip type and orientation presented consecutively and with each cue followed by a separate planning period. In one version of this task (OT task), the orientation information preceded the grip type information, while in the other version the cue sequence was reversed (TO task). D, Coronal MRI section (monkey J) with the recording chamber on the right hemisphere filled with contrast medium. The red line indicates the position of the oblique section in E. E, F, Maps of recording electrode penetrations (yellow dots) in monkeys J and L, respectively. The yellow ruler indicates the median (long tick mark) and quartiles of the recording distribution along the intraparietal sulcus (IPS). CS, Central sulcus.