Neuroplastic effects of transcranial near-infrared stimulation (tNIRS) on the motor cortex

Abstract

Near-infrared light stimulation of the brain has been claimed to improve deficits caused by traumatic brain injury and stroke. Here, we exploit the effect of transcranial near-infrared stimulation (tNIRS) as a tool to modulate cortical excitability in the healthy human brain. tNIRS was applied at a wavelength of 810 nm for 10 min over the hand area of the primary motor cortex (M1). Both single-pulse and paired-pulse measures of transcranial magnetic stimulation (TMS) were used to assess levels of cortical excitability in the corticospinal pathway and intracortical circuits. The serial reaction time task (SRTT) was used to investigate the possible effect of tNIRS on implicit learning. By evaluating the mean amplitude of single-pulse TMS elicited motor-evoked-potentials (MEPs) a significant decrease of the amplitude was observed up to 30 min post-stimulation, compared to baseline. Furthermore, the short interval cortical inhibition (SICI) was increased and facilitation (ICF) decreased significantly after tNIRS. The results from the SRTT experiment show that there was no net effect of stimulation on the performance of the participants. Results of a study questionnaire demonstrated that tNIRS did not induce serious side effects apart from light headache and fatigue. Nevertheless, 66% were able to detect the difference between active and sham stimulation conditions. In this study we provide further evidence that tNIRS is suitable as a tool for influencing cortical excitability and activity in the healthy human brain.

Computational modeling of the photon transport, tissue heating, and cytochrome C oxidase absorption during transcranial near-infrared stimulation

“…The physics was applied to each domain at steady state with the initial condition being zero. The source term was taken from the published literature[1] where the power density was 500mW/cm 2 at the scalp surface as presented by Chaieb and colleagues[1]. The head model was assumed to be surrounded by air at room temperature(25°C).…”

“…Near-infrared (NIR) light has been reported to be able to penetrate the extra-cranial layers like scalp, skull, cerebrospinal fluid and reach the superficial layers of the cerebral cortex due to the optical window. It has been hypothesized that interaction of NIR light with cytochrome c oxidase (CCO) can potentiate the CCO in the mitochondria, a component of the electron transport chain and key complex in energy production[1]. CCO is the primary chromophore in the mitochondria besides the calcium-ion channel (possibly mediated by opsin light absorption).…”

“…Since there is an increased absorption of longer wavelengths by water in the tissue, we postulate that NIR light interaction with neural tissue may have effects of photobiomodulation as well as photothermal neurostimulation which needs consideration for rational dosing of tNIRS due to the biphasic dose response. Although it has been reported that tNIRS is a modulator of cortical excitability in healthy human brain[1] which forms the basis of this paper, however, the exact mechanisms of the neuromodulation has been elusive. In this paper, we apply computational modeling to dissociate photothermal effects from photobiomodulation during tNIRS with 810nm while comparing that with the red spectrum (630nm and 700nm) used for LLLT[16] to investigate the mechanisms underlying neuromodulation [1].…”

“…Although it has been reported that tNIRS is a modulator of cortical excitability in healthy human brain[1] which forms the basis of this paper, however, the exact mechanisms of the neuromodulation has been elusive. In this paper, we apply computational modeling to dissociate photothermal effects from photobiomodulation during tNIRS with 810nm while comparing that with the red spectrum (630nm and 700nm) used for LLLT[16] to investigate the mechanisms underlying neuromodulation [1]. Here, the primary aim is to better understand the extent of optically induced tissue heating (primarily due to water and fat absorption) during tNIRS based on the experimental results by Chaieb et al [1].…”

Photobiomodulation with Near Infrared Light Helmet in a Pilot, Placebo Controlled Clinical Trial in Dementia Patients Testing Memory and Cognition

“…They used tNIRS at wavelength of 810 nm for 10 min over the hand area of the primary cortex and transcranial magnetic stim at 2.2 Tesla to assess levels of magnetic evoked motor-evoked- potentials of the dorsal interosseous in human brains in 55 healthy volunteers. They concluded that tNIRS is suitable as a tool for influencing cortical excitability and activity [14]. …”