Infrared light excites cells by changing their electrical capacitance

Optical stimulation has enabled important advances in the study of brain function and other biological processes, and holds promise for medical applications ranging from hearing restoration to cardiac pace making. In particular, pulsed laser stimulation using infrared wavelengths >1.5 μm has therapeutic potential based on its ability to directly stimulate nerves and muscles without any genetic or chemical pre-treatment. However, the mechanism of infrared stimulation has been a mystery, hindering its path to the clinic. Here we show that infrared light excites cells through a novel, highly general electrostatic mechanism. Infrared pulses are absorbed by water, producing a rapid local increase in temperature. This heating reversibly alters the electrical capacitance of the plasma membrane, depolarizing the target cell. This mechanism is fully reversible and requires only the most basic properties of cell membranes. Our findings underscore the generality of pulsed infrared stimulation and its medical potential

Perioperative HDR Brachytherapy for Reirradiation in Head and Neck Recurrences: Single-institution Experience and Systematic Review

Aim: The aim of our study was to evaluate the outcomes of patients reirradiated with high-dose-rate (HDR) intensity-modulated brachytherapy (IMBT) for recurrent head and neck cancer and to perform a systematic review of the literature. Materials and methods: Patients treated with prior radiation doses > 65 Gy were considered. After resection of macroscopic disease, catheters were fixed to the tumor bed. The total dose was 30 Gy in 12 fractions of 2.5 Gy twice daily for 5 days a week. A systematic literature search was conducted through several electronic databases including Medline/PubMed, Scopus, Embase and the Cochrane library. Results: Seventeen patients were included; median overall survival was 19 months with a median local control interval of 15 months. Median follow-up was 36 months. Seven papers were considered for the review. Conclusions: IMBT could play an important role in the retreatment of recurrent head and neck cancer

Radiant energy required for infrared neural stimulation

Infrared neural stimulation (INS) has been proposed as an alternative method to electrical stimulation because of its spatial selective stimulation. Independent of the mechanism for INS, to translate the method into a device it is important to determine the energy for stimulation required at the target structure. Custom-designed, flat and angle polished fibers, were used to deliver the photons. By rotating the angle polished fibers, the orientation of the radiation beam in the cochlea could be changed. INS-evoked compound action potentials and single unit responses in the central nucleus of the inferior colliculus (ICC) were recorded. X-ray computed tomography was used to determine the orientation of the optical fiber. Maximum responses were observed when the radiation beam was directed towards the spiral ganglion neurons (SGNs), whereas little responses were seen when the beam was directed towards the basilar membrane. The radiant exposure required at the SGNs to evoke compound action potentials (CAPs) or ICC responses was on average 18.9 ± 12.2 or 10.3 ± 4.9 mJ/cm(2), respectively. For cochlear INS it has been debated whether the radiation directly stimulates the SGNs or evokes a photoacoustic effect. The results support the view that a direct interaction between neurons and radiation dominates the response to INS