Behavioral task, muscle activity data, and recording sites. A: temporal sequence of the behavioral task in which monkeys were required to press a button with their left (top) or right hand (bottom). B: examples of electromyographic (EMG) activity shown in the flexor carpi ulnaris (FCU) muscles of the left and right arms, respectively. Activities in the left-press trials (orange) and right-press trials (green) are aligned with the performance of the button press. EMG activity was smoothed with a boxcar average of 11 time bins (i.e., 11 ms), and the light blue dashed lines indicate the first of 10 consecutive bins (10 ms) that exhibited a significant difference between the left-press and right-press trials (Welch's t-test, α = 0.01). The tick marks on the horizontal axis are placed at 200-ms intervals. C, left and middle: top views of the surfaces of the left frontal cortices of the 2 monkeys. The orange circles indicate the sites of penetration where the caudal cingulate motor area (CMAc) neurons were recorded; the electrode was advanced vertically in the dorsoventral direction. The green circles indicate the sites of penetration where the supplementary motor area (SMA) neurons were recorded; the electrode was inclined at a 10° angle lateral to the vertical axis. Open squares indicate sites where intracortical microstimulation (ICMS) was used to evoke movement (44 cathodal pulses, 200-μs width at 333 Hz, ≤80 μA) or where neurons responded to somatosensory stimuli in the CMAc (red) or SMA (blue); the corresponding body parts are labeled. The light blue dashed lines and numbers indicate the distance (mm) anterior to the Horsley-Clarke interaural plane. Right, coronal magnetic resonance images taken +17, +20, and +23 mm anterior to the Horsley-Clarke interaural plane in monkey 2. The thick lines indicate sites where electrodes penetrated the CMAc (orange) and SMA (green). Scale bars, 10 mm. L, left hemisphere; R, right hemisphere. Schematic at bottom right shows where neurons were recorded in the CMAc (orange) and SMA (green).