Figure 8

Interaction between electrical and optical stimuli reduces electrical thresholds. Example response images from a C57BL/6 neonatally AAV-injected mouse (A-D; up to 82% ChR2-H134R-EYFP transduced cells in the basal-mid turn region) or a ChR2-H134R-EYFP transgenic mouse (E–H) showing the spatial extent and rate of multi-unit activity across the recording array in response to RWM-applied 1 ms optical pulses (A, E), 100 µs/phase electrical pulses (B, F) or hybrid stimulation for which the electrical pulse was delayed by 1.75 ms relative to the optical pulse which was sub-threshold (63% of threshold optical power) (C, G). The dashed line/arrow between B and C shows the reduction in threshold afforded by the subthreshold optical stimulus applied prior to the electrical stimulation. (D, H) Difference plots to highlight activity that was greater or lower than the sum of the individual optical and electrical recordings in A-B or E–F. Response images were generated as per Fig. 4. The dotted lines on each spatial tuning curve compare the width of activation at an equivalent level above threshold (d’ = 1 above threshold). (I) Electrical thresholds for electrical stimulation alone (red) or when a subthreshold optical pulse was applied 1.75 ms prior to the electrical pulse (hybrid stimuli; purple) in the apex and RWM of the cochlea (n = 3 for injected mice and n = 1–3 for transgenic mice; a dashed line links data from the same mouse; individual mice are symbol-coded). Individual mice are symbol-coded. Basal turn data from ChR2-H134R-EYFP mice are a subset of the data presented in³⁵.