Figure 3. Chronos-mediated spiking provides a superior basis for pulse rate detection in the midbrain.

(a) Firing rates from individual trials within a 2 s period surrounding the onset of photostimulation in a Chronos⁺ mouse is plotted in 0.1 s bins. (b) The distribution of single trial firing rates from each bin falling within the spontaneous (−1 to 0 s) and evoked (0 to 1 s) periods, derived from the results in panel A. (c) For all three forms of stimulation, rates from both periods are then converted into z-scores and the absolute values used as rectified z-scores, where more positive values represent deviations in firing rate that could support a neural code for detection. (d) the separation between the spontaneous and evoked z-score distributions is expressed with the d’ metric to quantify the utility of a rate code for detecting sound or photostimulation.