The direction changes employed for the head-fixed detection task differ from the amplitude deviants used throughout the rest of the study. We therefore also examined the impact of weak L6 CT drive on the neural representation of direction deviations in separate recordings. In L6 CT (GCaMP6s imaging, N = 83 sensory responsive neurons), encoding of stimulus direction was disrupted by weak optogenetic drive (P<0.05, baseline direction and direction changes). Similarly, L2/3 and L4 neurons (N=92 units and MUA recordings) became more sharply tuned to preferred directions during optogenetic activation (P=0.038 left tailed, change in spike count for preferred over non-preferred), rather than increasing firing rates for deviants (P=0.003 right tailed decrease). These findings parallel the effects observed using amplitude deviants. (a) Stimulus design for electrophysiological study of directional deviants, same as for head-fixed behavioral stimulus detection task (9 sessions). Baseline direction was randomly chosen (see Methods). Spike rate increase to preferred deviant direction (N=92 units and MUAs) relative to baseline. Preferred direction was determined by the tuning to baseline stimuli. L6 activation increased the relative response to the preferred versus non-preferred direction (rank sum, p=0.038 left tailed increase in spike count increase for preferred). Spike rates were increased for directional deviants (relative to baseline, directions are balanced). L6 drive removes this change encoding (p=0.003 right tailed decrease in additional spikes). (b) Direction encoding in L6 CT cells assessed using simultaneous 2-photon imaging and optogenetics, (83 cell bodies, GCaMP6s, see main text and methods). Top: L6 CT cells preferentially responded do either trains of upwards, followed by downwards deflections or vice-versa (P<0.0001 rank-sum, 8 deflections, 10Hz, see Methods). For each trial, all other trials of that L6 CT cell body in the same session were analyzed to determine the preferred stimulus and the held out trial was counted either as preferred or non-preferred for the analysis.Bottom: Same analysis, but whole trains of vibrissa deflections were made up of upwards or downwards deflections. L6 CT significantly encoded direction (P=0.0016). Weak L6 drive disrupted the encoding of deflection direction in L6 CT cells, in both cases (reduction of differences across preferred and non-preferred between control and laser conditions P<0.0001 via non-paired bootstrap across trials in both cases, P<0.0001 paired by cell via bootstrap).