Fig. 3: Inner hair cells display both independent and coordinated spontaneous calcium activity in vivo.

a Still images from a timelapse recording from a P8 GCaMP6f^fl/flMyo15-Cre^+/-mouse, displaying the propagation of spontaneous Ca²⁺ activity across multiple nearby IHCs. Each image represents an average of 30 frames from the original recording. b Fluorescence traces highlighting Ca²⁺ activity in a 20-minute recording from 19 IHCs from a P4 mouse. Traces represent Ca²⁺ activity from adjacent IHCs, some of which occurred simultaneously in several cells (arrowheads). These coordinated events appeared alongside less prominent uncorrelated, single-cell transients (arrows). c, Percentage of events with Ca²⁺ transients in “single” or “multiple” ( > 2 IHCs) events. Note that 2-cell events (15%) were excluded to minimise any misrepresentation of random coincidental events. Each datapoint represents an individual IHC (P3-P10, 740 active IHCs out of 776, 28 mice). Average data are shown as mean ± SD. d Number of IHCs involved in coordinated activity as a function of age. Each data point represents a multicellular event (i.e. Ca²⁺ transients occurring simultaneously in >2 IHCs). Number of events from left to right: 86, 157, 295, 200, 105, 347, 47, 23 from the P3-P10 IHCs in Fig. 2a (31 mice). Data are shown as mean ± SD. At all ages tested, coordinated Ca²⁺ events were observed in up to about 20 cells simultaneously; this value could be slightly underestimated because in a few recordings the longitudinal spread of the Ca²⁺ transients exited the field of view. e Correlation matrix computed from the Ca²⁺ traces in panel b. Coordinated activity resulted in a high degree of correlation between nearby IHCs. f Average correlation coefficient (solid line: average Pearson correlation coefficient; shaded area: standard deviation) as a function of the distance between IHCs.