For spine images (Fig. 4-5), circular ROIs were placed over individual dendritic spines to measure spine fluorescence and compute ΔF/F0_spine. To minimize contamination from back-propagating action potentials (BAPs), we either recorded from ‘silent cells’ (∼ 40 % of cells) showing few or no APs in response to a standard set of grating stimuli (Fig. 4), or used stimuli with reduced stimulus contrast (Fig. 5).
