Figure 1.

Population data showing four statistically defined classes of cells (single-units) in superior colliculus according to the responses evoked by fictive whisking. The four classes of cells include: (1) cells that are responsive to whisking movement only, (2) cells that are responsive to movement and active touch (whisking on a surface) excites them further, (3) cells that are responsive to movement and active touch inhibits the movement response, and (4) cells that are only responsive to active touch. Responses are shown at four different whisking frequencies during whisking in air (Whisk) and whisking on surfaces of different roughness (g60, g220, g600). Bottom, The whisker movement (angle in degrees) measured with video tracking during fictive whisking (positive values indicate that the whiskers protracted). Train refers to five pulses delivered at 100 Hz.