Fig. 2.

Responses of 1 unit to passive joint manipulation. A, top: continuously recorded activity on 1 electrode filtered with a 4-pole Butterworth filter between 500 and 3,000 Hz to reveal spiking activity. Waveforms assigned to unit 1 on this channel are shown in red. Bottom, firing rate of the unit marked in red, calculated by convolving spike waveform with a hamming window 1 s long. Yellow rectangles mark the epochs during which the experimenter passively extended the wrist. Gray rectangles mark the epochs during which the joint was flexed back to its starting position. B: raster plot of the responses from the same unit. Each dot represents a detected action potential. Horizontal lines separate passive manipulation blocks. In each block a row represents 1 trial of the passive movement indicated on the vertical axis. All trials were aligned on the go cue delivered to the experimenter (thick vertical line). Yellow and gray regions represent movement epochs in the direction indicated on the vertical axis and back to starting position, respectively. Right-side manipulations: WF, wrist flexion; WE, wrist extension; WU, wrist ulnar deviation; WR, wrist radial deviation; WP, wrist pronation; WS, wrist supination; EF, elbow flexion; EE, elbow extension; SF, shoulder flexion; SE, shoulder extension; SD, shoulder adduction; SB, shoulder abduction; RK, right knee extension. Left-side manipulations (ipsilateral to array): LP, left wrist pronation; LK, left knee extension.