Fig. 3. Targeted photostimulation elicits a suppressive network response that scales with the strength of coincident sensory stimuli and the functional identity of neurons.

a Example STA traces to visual only trials across contrasts in one experiment. Neurons are sorted by their average response across all contrasts. Black line indicates visual stimulus presentation. b The neural responses across the whole population in the more engaged state are significantly larger than in the less engaged state (n = 28 sessions, 12 mice). The ratio of hits and misses within each contrast have been matched across states. The line and shading represents the mean ± SEM. Individual points across the two curves were tested with two-sided Wilcoxon sign rank test with multiple comparison (Bonferroni) correction for number of contrasts. The average pooled responses were compared with a two-sided Wilcoxon sign rank test. *** denotes P < 0.001 and ** P < 0.01. c Top: example experimental volume. ROIs are colored by the change in activity caused by photostimulation during spontaneous gray screen periods. Vertical red lines indicate the directly stimulated cells. Bottom: example types of responses seen when the visual stimulus is paired with photostimulation. d Target cell responses. Left: responses to visual only trials across contrasts. Middle: responses to paired visual and photostimulation. Right: the change in activity caused by photostimulation. Target cells are strongly activated by photostimulation. The level of activation is significantly higher in the engaged state. The ratio of hits and misses within each contrast have been matched across states. The line and shading represents the mean ± SEM (n = 28 sessions, 12 mice). Comparisons were made with a two-sided Wilcoxon sign rank test. *** denotes P < 0.001. e Background cell responses. Left: The responses of all background neurons to visual only trials. Middle: The response of background neurons to paired visual and photo-stimulation. Right: The change in activity of background cells caused by photostimulation. The background cells are suppressed on average, across all contrasts. No difference is seen in the level of suppression between behavioral states. The line and shading represents the mean ± SEM (n = 28 sessions, 12 mice). Comparisons were made with a two-sided Wilcoxon sign rank test. ** denotes P < 0.01. f Top: the 2D spatial profile of photostimulation influence. All neurons are aligned relative to their nearest target spot (at 0,0), collapsed across z-planes. Spatially binned (5 ×5 µm), and Gaussian filtered (SD = 10 µm) for display only. A central hotspot of activity corresponds to directly targeted neurons. Surrounding the targeted neurons the predominant effect of photostimulation is suppression of neighboring cells (n = 28 sessions, 12 mice). Bottom: the 1D spatial profile of photostimulation influence. No difference is seen between the two states. The line and shading represents the mean ± SEM (n = 28 sessions, 12 mice). g Presenting the average network responses across all sessions on two axes; visual stimulus contrast and similarity to the target cells (quantified as the Pearson’s correlation of a given cell’s contrast response curve to that of the average target neuron). The top row corresponds to the directly targeted neurons. Left: responses to visual stimuli of increasing contrast alone. Note cells positively correlated with the target cells respond positively to increasing contrast. Middle: The responses to paired visual and photo-stimulation. Right: The difference reveals the change in activity caused by photostimulation. Note that cells similar to the target cells are more strongly suppressed at higher contrasts (n = 28 sessions, 12 mice). h The change in activity of background cells. Background neurons most similar to the target neurons show the strongest levels of suppression mediated by the photostimulation (green line). The level of suppression recruited increases as the visual contrast increases. (2-way ANOVA grouped by state and contrast. Effect of contrast F(4) = 11.9, P < 0.001. Effect of similarity F(19) = 2.9, P < 0.001. Interaction of contrast and similarity F(76) = 2.5, P < 0.001, n = 28 sessions, 12 mice). Lines show the mean and shading shows the SEM. i The relationship between the slope of suppression recruited by increasing visual contrasts, versus the functional similarity to the photostimulated neurons. Neurons within a similarity group are pooled across experiments and the slope of suppression versus contrast is computed. Error bars indicate the standard error of the fit, obtained by resampling animals/sessions with replacement. Neurons most similar to the target neurons are increasingly suppressed as contrast increases, which corresponds to a negative slope. Filled individual points indicate individually significant fits with Bonferroni multiple comparison correction. The line of best fit indicates the relationship across functional similarity groups of all the background cells, shading represents the CI of the fit. The directly stimulated neurons are shown at the far right and are excluded from the fit (n = 28 sessions, 12 mice).