Similar to immature and mature animals, costimulation of the surround suppressed neuronal responses and increased their selectivity in dark-reared mice (Figures 6A and 6B; firing rate change RF + natural surround, –60.7% ± 7.9%, p < 0.001; RF + phase-randomized surround, –52.3% ± 10.3%, p < 0.001, n = 15; t test), Ribociclib indicating that the capacity of visual circuits for surround modulation was maintained and not disrupted by rearing animals devoid of visual experience. Importantly, however, we observed no significant

differences between the effects of the natural and phase-randomized surrounds on responses to stimuli in the RF (Figure 6B) in terms of firing rate (RF + natural versus RF + phase-randomized surround, p = 0.33, paired t test), response selectivity (p = 0.23, paired t test), or information transmitted per spike (p = 0.88, paired t test). Differences in the level of spike suppression were not related to differences in absolute firing rates in any age

group (Figure S6). CP-673451 order The indifference of dark-reared V1 neurons to the statistical properties of surround stimuli was also reflected at the level of subthreshold membrane potential dynamics (note that the cellular sensitivity for spiking to membrane potential changes was comparable to the other age groups; Figure S5; Azouz and Gray 2003). The median Vm in dark-reared mice was not significantly altered by costimulation of RF and surround (Figures 6C and 6D, n = 19; p = 0.33; Friedman’s test). Similar to normally reared, mature mice, there was a strong dependence of ΔVm (Figure 6E) on the level of Vm depolarization during stimulation of the RF Rutecarpine alone (Figures 6G and 6H). However, the distribution of ΔVm was not different between natural and phase-randomized surround stimulation conditions (Figure 6F, p = 0.21, Wilcoxon rank sum test), and ΔVm at most depolarized Vm during RF stimulation was not significantly different

when costimulating the surround with natural and phase-randomized stimuli (Figures 6G and 6H) in dark-reared V1, similar to the observations in immature V1 (Figures 3F–3J). Accordingly, while the likelihood of spiking during large-amplitude depolarizing events (which were unaltered in frequency of occurrence across conditions; Figure 6J; p = 0.82, Kruskal-Wallis test) was reduced, it was not significantly different between the two surround conditions (Figure 6I; p = 0.18, Kruskal-Wallis test across all conditions). These findings are consistent with a similar level of firing rate suppression by phase-randomized and natural surround stimuli (Figure 6B) in these visually inexperienced but mature animals. Thus, the emergence of neuronal sensitivity for image features extending beyond the RF boundaries requires visual experience after eye opening. Our findings provide evidence for a progressive developmental refinement of visual processing to the global statistics of the natural environment, as hypothesized previously (Olshausen and Field, 1996, Berkes et al.