Infrared Laser Pulses Excite Action Potentials in Primary Cortex Neurons In Vitro.

Infrared neural modulation (INM) has been well studied in the peripheral nervous system (PNS) for potential clinical applications. However, limited research has been conducted on the central nervous systems (CNS). In this study, we aimed at investigating the feasibility of using pulsed infrared (IR) laser with a wavelength of 1940 nm to excite network activity of cultivated rat cortex neurons.We cultured rat cortex neurons, forming neural networks with spontaneous neural activity, on glass multi-electrode arrays (MEAs). Laser at a power of 600 mW and a pulse rate of 10 Hz were used to stimulate the neural networks using the optics of an inverted microscope. Pulse durations were varied from 200 µs to 1 ms. The spike rate was calculated to evaluate the change of the neural network activity during the IR stimuli and the corresponding frequency components of neural response were calculated to examine whether recorded spikes were evoked by the IR pulse or not. A temperature model was adapted from a previous study to estimate the temperature rise during laser pulsing.We observed that the IR irradiation with a pulse duration of 800 µs and 1 ms could excite neuronal action potentials. The temperature rose 18.5 and 23.9 °C, for pulse durations of 800 µs and 1 ms, respectively. Thus, in addition to previously shown inhibition of IR irradiation with a wavelength of 1550 nm, we demonstrate an optical method that can modulate neural network activity in vitro. The preliminary results from this paper also suggested that MEA recording technology coupled with a laser and microscope systems can be exploited as a new approach for future studies to understand mechanisms and characterize laser parameters of INM for CNS neurons.

Optical stimulation of primary motor cortex with 980nm infrared neural stimulation.

To explore the penetration depth with short-wavelength infrared light, 980 nm pulse infrared light was used to stimulate the primary motor cortex of rat. The heating model was created to simulate the temperature distribution for 1875 nm and 980 nm infrared neural stimulation. Post-stimulus time histogram was used to observe the neural response induced by Infrared neural stimulation on primary motor cortex. The model predicted the penetration depth of 980 nm was deep into 1.2 mm. Cortical neural located between 500 µm to 1000 µm were successfully activated by 980 nm INS. The preliminary results suggested that, 980 nm pulse INS could serve as a candidate for deep tissue stimulation.