highly significantp < 0.001
A unit was defined as “opto-tagged” if the following two criteria were met: (1) Firing rate increased with laser pulse onset and this increase was highly significant (t-test p < 0.001), both within 10 ms of laser pulse onset and over the pulse duration (25ms), compared to the 25ms window before pulse onset; (2) spike shape was similar during laser-on and laser-off periods (correlation coefficient >0.9) ( Figure 1 D).