(A) Relative spike rate versus lateral distance from the photostimulus center for various laser powers. Pyramidal neurons only. Blue light (437 nm) photostimulation in barrel cortex, n = 198; blue light photostimulation in motor cortex, n = 236; blue light photostimulation in ALM, n = 335; red light (635 nm) photostimulation in ALM, n = 236. Neurons were pooled across cortical depths. Mean ± s.e.m., bootstrap across neurons. (B) Photoinhibition strength versus spatial spread. Relative spike rate is the average across all pyramidal neurons near laser center (<0.4 mm, all cortical depths). Spatial spread is the distance at which photoinhibition strength is half of that at the laser center (‘radius, half-max’). Each circle represents data from one photostimulation power. Lines connect all circles of one method. VGAT-ChR2-EYFP, Emx1-IRES-Cre x Ai35D, Emx1-IRES-Cre x Camk2a-tTA x Ai79, data from Figure 5J replotted here for reference.