Functional connectivity of brain networks with three monochromatic wavelengths: a pilot study using resting-state functional magnetic resonance imaging

Abstract

Exposure to certain monochromatic wavelengths can affect non-visual brain regions. Growing research indicates that exposure to light can have a positive impact on health-related problems such as spring asthenia, circadian rhythm disruption, and even bipolar disorders and Alzheimer’s. However, the extent and location of changes in brain areas caused by exposure to monochromatic light remain largely unknown. This pilot study (N = 7) using resting-state functional magnetic resonance shows light-dependent functional connectivity patterns on brain networks. We demonstrated that 1 min of blue, green, or red light exposure modifies the functional connectivity (FC) of a broad range of visual and non-visual brain regions. Largely, we observed: (i) a global decrease in FC in all the networks but the salience network after blue light exposure, (ii) a global increase in FC after green light exposure, particularly noticeable in the left hemisphere, and (iii) a decrease in FC on attentional networks coupled with a FC increase in the default mode network after red light exposure. Each one of the FC patterns appears to be best arranged to perform better on tasks associated with specific cognitive domains. Results can be relevant for future research on the impact of light stimulation on brain function and in a variety of health disciplines.

The Impact of the Wavelength and Its Transmittance on the Visual Evoked Potentials, at Baseline, and under the Effect of Six Monochromatic Filters Used for Visual Treatments

“…As represented by facts, in these four participants, violet-blue-green filters acted like inhibitors, causing depression of neuronal networks [33]. A global decrease in functional connectivity in most networks was found after a minute of green and blue light exposure through a fMRI study [28], which leads us to the same conclusion, namely, that these ranges of wavelengths can modify brain networks which are arranged to perform better on tasks associated with specific cognitive demands. An increment on the LAT DIFF LT-RT was observed in 58.3% of the cases, against 37.5% that presented a decrease in its value.…”

“…However, what we know from quantitative electroencephalography studies, is that light stimulation and phototherapy which employs a combination of two or more of these wavelengths (mu-alpha, omega-neurasthenic, alphaomega etc), can modulate the alpha-wave, interhemispheric connections, anteroposterior gradient, and brain coherence [26,27]. Likewise, a pilot study on healthy participants showed that functional connectivity patterns on brain networks measured with fMRI, are light-dependent [28]. Therefore, we expect to see the effect of these monochromatic filters on the visual pathway, which connects the eyes to the cortex and modulates neural activity.…”

“…There are no VEP studies in the literature that report the effect on the neural activity of monochromatic filters designed to treat SA patients, to propose posteriorly successful treatments based on scientific evidence. What we know from quantitative electroencephalography studies, however, is that light stimulation and phototherapy which employs combination of two or more of these wavelengths can modulate the Alpha-wave, interhemispheric connections, anteroposterior gradient, and brain coherence [26,27], and functional connectivity patterns on brain networks measured with fMRI, are light-dependent [28]. Therefore, we expect to see the effect of these monochromatic filters on the visual pathway, which connects the eye to the cortex and modulates neural activity.…”

Temporal and spectral analyses of EEG microstate reveals neural effects of transcranial photobiomodulation on the resting brain

“…Previous studies on the functional significance of EEG microstates ( Britz et al, 2010 ; Milz et al, 2016 ; Seitzman et al, 2017 ) have suggested that microstate A is associated with the auditory network, while microstate D is related to the dorsal attention network (DAN). A recent study using resting-state fMRI ( Argilés et al, 2022 ) also reported an alteration in the functional connectivity of the DAN after red light exposure. Moreover, several papers have reported significant enhancement of attention and memory induced by tPBM ( Barrett and Gonzalez-Lima, 2013 ; Hwang et al, 2016 ; Vargas et al, 2017 ; Jahan et al, 2019 ).…”

Efficacy of optometric phototherapy: a systematic review

“…However, other studies such as Ibrahimi et al 1 have currently reported that the use of this light therapy may produce changes in the metrics of cortical activity in patients with strabismus and amblyopia. Argilés et al 24 have also reported that the use of Syntonic therapy can modify the functional connectivity of a broad range of visual and non-visual brain regions. Accordingly, even though some clinicians use phototherapy as a visual therapy for several visual conditions, there seems to be a lack of evidence about the efficacy of this technique.…”