Infrared neural stimulation and inhibition using an implantable silicon photonic microdevice

Brain is one of the most temperature sensitive organs. Besides the fundamental role of temperature in cellular metabolism, thermal response of neuronal populations is also significant during the evolution of various neurodegenerative diseases. For such critical environmental factor, thorough mapping of cellular response to variations in temperature is desired in the living brain. So far, limited efforts have been made to create complex devices that are able to modulate temperature, and concurrently record multiple features of the stimulated region. In our work, the in vivo application of a multimodal photonic neural probe is demonstrated. Optical, thermal, and electrophysiological functions are monolithically integrated in a single device. The system facilitates spatial and temporal control of temperature distribution at high precision in the deep brain tissue through an embedded infrared waveguide, while it provides recording of the artefact-free electrical response of individual cells at multiple locations along the probe shaft. Spatial distribution of the optically induced temperature changes is evaluated through in vitro measurements and a validated multi-physical model. The operation of the multimodal microdevice is demonstrated in the rat neocortex and in the hippocampus to increase or suppress firing rate of stimulated neurons in a reversible manner using continuous wave infrared light (λ = 1550 nm). Our approach is envisioned to be a promising candidate as an advanced experimental toolset to reveal thermally evoked responses in the deep neural tissue. Researchers in Hungary have developed a probe that can activate or inhibit neurons using infrared light while simultaneously measuring their cellular activity. A team led by Zoltan Fekete of Pazmany Peter Catholic University built and tested the device, which combines an optical waveguide to deliver the infrared light with wiring and measurement sites to record neural potential. The infrared beam heats a region of ~0.02 mm². The change in temperature can stimulate or inhibit neuronal firing, and the probe measures these changes in their behavior. The team tested the probe in the neocortex and hippocampus of rats and measured reversible changes in neural activity in both regions. The new photonic probe will enable researchers to investigate the effect of temperature fluctuations on neurophysiology and brain activity, including its role in neurodegenerative disease or brain injuries.