We imaged GCaMP6s-expressing neurons through a chronic imaging window6,31 over several weeks in V1 (Supplementary Fig. 6c)18. Sensory responses and orientation tuning of neurons were largely stable (Supplementary Fig. 6c, e). Responses of a small fraction of neurons were lost over time, which was balanced by other neurons that started responding. The orientation preference of the neurons responding in all imaging sessions (∼56% of cells that responded in the first session) was remarkably stable (Supplementary Fig. 6d). Over months of expression a small fraction of highly expressing neurons acquired nuclear fluorescence; these neurons eventually also developed aberrant responses11 (Supplementary Fig. 7). These experiments indicate that expression of GCaMP6s over 1-2 months does not obviously perturb the function of cortical circuits.
