Over development, spontaneous activity (SA) in primary visual cortex (V1) becomes increasingly similar to stimulus evoked activity (EA) (Berkes et al, Science 2011). This increasing similarity has been taken to reflect a progressive adaptation of the animal’s internal models to the statistics of the environment (Berkes et al, 2011). An alternative interpretation (Okun et al, Soc Neurosci Abstr 2011) suggests these effects can be obtained with a simple model that only matches the mean firing rate on each electrode and the distribution of population rates, but not detailed patterns of pairwise correlations between neurons. Hence, the increased similarity between SA and EA in adult animals could be simply a reflection of changes in these network properties, without necessarily implying the learning of a model of the environment (Okun et al, 2011). To test this hypothesis directly, we created surrogate data by fitting maximum entropy models to the original data recorded in ferret V1 (Berkes et al, 2011) matching the mean firing rates of all individual channels and the distribution of population rates, as suggested by Okun et al. We then compared these surrogate data to the original. In line with the analysis of Okun et al (2011), we found that similar results to those described by Berkes et al (2011) could be obtained if the true response distributions were only constrained by single neuron firing rates and population rate distributions. However, in contrast to the prediction of Okun et al (2011), the true response distributions were found to become increasingly dissimilar from their surrogate versions, and this difference was important in matching SA and EA. In a parallel submission (Fiser et al) we also report that in lid sutured animals the specificity of the match between SA and EA to natural scenes is disrupted, suggesting a direct role of visual experience in its development. Overall, our results support the view that learning is indeed one of the factors driving the increase in similarity between spontaneous and evoked activity in primary visual cortex.

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