Availability and safety assessment of infrared neural stimulation at high repetition rate through an implantable optrode

An implantable optrode with micro-thermal detectors was designed to investigate the availability and safety of INS using high repetition rates. Optical auditory brainstem responses (oABRs) were recorded in normal-hearing guinea pigs, and the energy thresholds, pulse durations, and amplitudes evoked by the varied stimulus repetitions were analyzed. Stable oABRs could be evoked through INS even as the repetition rate of stimulation reached 19kHz. The energy threshold of oABRs was elevated, the amplitudes decreased as pulse durations increased and repetition rates were higher, and the latencies were delayed as the pulse durations increased. The temperature variation curves on the site of stimulation significantly increased as the pulse duration increased to 400 mu s. INS elevated the temperature around the stimulus site area via thermal accumulation during radiation, especially when higher repetition stimuli were used. Our results demonstrate that high repetition infrared stimulations can safely evoke stable and available oABRs in normal-hearing guinea pigs.