Pulsed 808-nm infrared laser stimulation of the auditory nerve in guinea pig cochlea.

Pulsed near-infrared radiation has been proposed as an alternative stimulus for auditory nerve stimulation and could be potentially used in the design of cochlear implant. Although the infrared with high absorption coefficient of water (i.e., wavelength ranged from 1.8 to 2.2 µm) has been widely investigated, the lymph in the cochlea absorbs most of the infrared energies, and only a small part can arrive at the target auditory nerves. The present study is aimed to test whether the short-wavelength near-infrared irradiation with lower absorption coefficients can penetrate the lymph fluid to stimulate the auditory nerves. An 808-nm near-infrared laser was chosen to stimulate the auditory nerve in the guinea pig cochlea. The infrared pulse was delivered by an optical fiber that was surgically inserted near the round window membrane and oriented toward the spiral ganglion cells in the basal turn of the cochlea. The 2-Hz infrared pulses were used to stimulate the cochlea before and after the deafness with different pulse durations (100-1,000 µs). Optically evoked compound action potentials (oCAPs) were recorded during the infrared radiation. We successfully recorded oCAPs from both normal hearing animals and deafened animals. The oCAP amplitude increased with the infrared radiation energy. The preliminary experiment suggests that the near-infrared with lower absorption coefficients can effectively pass through the lymph filled in the cochlea and stimulate the auditory nerve. Further studies will optimize the deafness animal model and determine the optimal stimulation parameters.

Irradiation of 850-nm laser light changes the neural activities in rat primary visual cortex.

Although infrared laser was proven to be an alternative approach for neural stimulation, there is very little known about the neural response to infrared laser irradiation in visual cortex. This study is to investigate the effect of near-infrared laser irradiation on neural activities at the cortex level. A 850-nm pigtailed diode laser was applied to stimulate the rat primary visual cortex while the horizontal black and white stripe pattern was used as standard visual stimulation to evoke visual-evoked potential (VEP). Both amplitude and latency of VEP P100 was measured with or without infrared pulse stimulation applied in rat primary visual cortex. Paired t test and one-way analysis of variance were used to evaluate the impact of infrared irradiation and its pulse width on the amplitudes and latencies of P100, respectively. The results from our preliminary study revealed that, the pulsed near-infrared laser depressed the VEP amplitude and shortened the latency of P100; with the increment of pulse width of infrared irradiation, further decline of VEP amplitude and much shortened latency of P100 were observed. The present work suggests that near-infrared laser irradiation can alter the neural activities in primary visual cortex transiently, and could provide a novel contactless artificial neural stimulus to brain cortex with high spatial selectivity.

Optical stimulation of visual cortex with pulsed 620-nm red light.

To explore the optical neural stimulation with visible light, 620-nm red light pulse emitted by LED was used to stimulate the left primary visual cortex of adult rat. The neural response in right primary visual cortex was recorded with a flexible microelectrode. By synchronized averaging the raw signal, optical evoked potentials (OEPs) were observed a negative wave and positive wave after optical stimuli. Furthermore, the amplitude and occurrence of the negative and positive wave were modulated by the strength and pulse width of the optical stimulus. The preliminary experiment suggested that, beyond the infrared laser, the pulse of visible light (e.g. red light) can modulate the neural activity in central nervous system.