Figure 6.

Trigeminal ganglion activity is phase locked to the tactile stimulus contact and does not appear during the anticipatory firing period. A, Example of trigeminal ganglion PSTHs during active aperture discrimination. The panels show PSTHs (10 ms bins), with respect to the aperture bar beam break (time = 0), of trigeminal ganglion single unit and multiunits recorded during the tactile discrimination task. Between the door (blue) and the beam break (red), there is an overall reduction or absence of activity in the TG neurons, indicating that no whisker movements or contacts are present during this period. B, Each row in the panel represents the activity of a single unit or multiunit, normalized to its maximum firing rate, during a session. Each of the different colors represents a variation in the firing rate, with red indicating excitation, and deep blue indicating inhibition. Time 0 corresponds to the discrimination bar beam break. Units were ordered by the maximum firing rate in 0 to 0.25 s. A total of 736 units and multiunits recorded from five rats in 28 sessions are presented. The periods of increased activity reflect whisker contacts with the door, discrimination bars and center nose poke. A marked decrease in TG firing rate is observed in the period −0.25 to 0 s between the door and the discrimination bars. C, The activity levels presented for TG, VPM, and S1 were recorded simultaneously (n = 3 rats). Between the door and the discrimination bars (from −250 to 0 ms), both VPM and S1 presented a significant group of cells with increased activity. In the trigeminal ganglion, this activity was almost absent (for details, see Results). Comparison of the fraction of significant increased responses (red lines in right column) showed that both VPM and S1 presented anticipatory increases in activity that did not match the TG increase. However, immediately after the beam break, all three regions presented a simultaneous peak of increased activity. D, Each column demonstrates PSTHs of neurons recorded from the same session in three different animals. While the TG presented a marked reduction of activity in the 250 ms before the BB, sustained or phasic increases in the VPM and S1 could still be observed. The presence of S1 and VPM modulations in the absence of TG activity indicate that the origin of anticipatory activity cannot be due to the activation of primary whisker afferents from the TG.