Figure 4. Passive stimulations and neural response properties.

A, upper schematic diagram: pattern of multiwhisker ramp-and-hold passive stimuli delivered to anaesthetized rats. Large black dots represent stimulation of a particular whisker. Upward arrows show stimulation onsets. Lower schematic diagram: stimulation pattern of the awake, restrained rats. B, left, schematic diagram of the moving aperture stimulus. Aperture is accelerated across the facial whiskers (with variable onsets and velocities) by the pneumatic solenoid and also simultaneously deflected laterally in varying amounts by the DC servo in order to accurately replicate the range of whisker deflection dynamics that occurred during active discrimination. Right, video frame captures showing an example of the aperture moving caudally across the whiskers of an awake restrained rat while simultaneously deflecting laterally 5 mm (to the right) over a 200 ms interval. C, representative single-unit responses showing long-duration, tonic activation during active discrimination. Upper portion of each panel is a raster plot where each line represents a consecutive trial in a recording session and each dot is a unit spike; lower portion of each panel shows summed activity for all trials in 5 ms bins. The 0 time-point represents the moment that rats disrupted the aperture photobeam (Fig. 1). D, representative single-unit responses evoked by passive ramp-and-hold stimulation of 16 whiskers in lightly anaesthetized rats (upper panel) and by passive stimulation of 8 whiskers in awake, restrained rats (lower). The 0 time-point represents stimulus onset. E, representative single-unit responses evoked by moving aperture stimulation of awake, restrained rats (0 time-point represents onset of aperture movement). F, mean (+ s.e.m.) excitatory response duration and magnitude evoked during the active discrimination and by the different passive stimuli delivered to anaesthetized or awake restrained rats. From Krupa et al. (2004). Reproduced with permission.