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In the mammalian primary visual cortex, most of the neurons respond selectively to a preferred orientation of visual stimuli and among these neurons a subpopulation displays additionally direction-selective responses. Previous studies in the ferret visual cortex indicated that the development of direction selectivity, but not that of orientation selectivity requires early visual experience (Li et al. 2006). Interestingly, a recent report demonstrated that in the mouse retina direction selectivity is established early in development and independently of visual experience (Elstrott et al., 2008). Thus, an important question concerns the role of visual experience for the development of direction selectivity in the mouse visual cortex.In the present study, we investigated the development of direction selectivity in the mouse primary visual cortex by using in vivo fast scanning two-photon imaging and the multi-cell bolus loading (MCBL) technique with fluorescent calcium indicator Oregon Green BAPTA-1. We imaged the responses of layer 2/3 neurons to oriented moving gratings with single-cell resolution at different developmental stages, starting around eye-opening (P11-P16) to adulthood (P60-P100).

Before eye-opening, only strong light flashes could elicit light-evoked responses in the visual cortex. The first direction-selective neurons were detected soon after eye-opening, but not before. Remarkably, in contrast to the results obtained in the ferret visual cortex, direction-selective but not orientation-selective neurons were predominant at this early stage in the mouse visual cortex. The proportion of direction- and orientation selective neurons gradually increased during development from approximately 10% at the first week after eye-opening to 50% in 2-month-old mice. The presence of direction-selective neurons around eye-opening suggested that this feature is established in the absence of visual experience. This hypothesis was supported by the observation that direction-selective neurons were also present in dark-reared mice. Taken together with results from other studies, our findings suggest that direction-selectivity is an intrinsic feature of the mouse visual system that is preserved over several levels of signal processing, from the retina to the primary visual cortex.