Cerebral hemodynamic effects of transcranial infrared laser stimulation measured with functional near-infrared spectroscopy

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Abstract

Transcranial infrared laser stimulation (TILS) is a novel, safe, non-invasive treatment that increases brain energy metabolism by increasing blood flow, blood oxygen content, and the enzymatic activity of cytochrome oxidase via photonic energy absorption. Our group has previously shown that TILS can result in improvements in cognitive performance in healthy adults, in terms of sustained attention (as measured by the psychomotor vigilance test, or PVT) and visuospatial short-term memory (as measured by the delayed match-to-sample task, or DMS). To explore the brain metabolic mechanisms by which this enhancement in performance occurs, functional near-infrared spectroscopy (fNIRS) was used to measure changes in oxygenated and deoxygenated hemoglobin as a result of both TILS and behavioral testing with PVT and DMS tasks. fNIRS is a safe, non-invasive way of indirectly monitoring brain activity, by transmitting two wavelengths transcranially and measuring the amount of light that reaches nearby detectors. The two wavelengths correspond to the absorption spectrum of oxygenated and deoxygenated hemoglobin, respectively. Hemodynamic responses in healthy participants were assessed with fNIRS at baseline, and during the PVT and DMS tasks. TILS was administered next, and fNIRS was used again immediately after TILS, and again during PVT and DMS. Data collection and analysis is ongoing. This experimental design will allow the decomposition of brain metabolic effects into those due to functional activation from PVT/DMS tasks, those due to TILS, and any interactions between the two. This approach may be used to monitor the successful effects of laser stimulation on cerebral oxygenation.

Authors

• Emma Holmes, University of Texas at Austin

• Douglas W. Barrett, The University of Texas at Austin

• F. Gonzalez-Lima, The University of Texas at Austin