neurons originates from (presumably orientation-tuned) V1 neurons34. Neighboring spines were often tuned with different preferred orientations. The correlation between orientation tuning and distance between spines was weak (R=0.08; p>0.05). Overall, 27% of spines (62/228, 15 dendrites, 4 mice) were visually responsive, and most were orientation-tuned (Fig. 4f, g). Furthermore, close to 40% of spines were active at some time during the imaging session (Fig. 4f). Bleaching of GCaMP6 was negligible over 40 imaging trials (320 s of continuous imaging, Fig. 4h).
