Wearable functional near infrared spectroscopy (fNIRS) and transcranial direct current stimulation (tDCS): expanding vistas for neurocognitive augmentation

Abstract

Contemporary studies with transcranial direct current stimulation (tDCS) provide a growing base of evidence for enhancing cognition through the non-invasive delivery of weak electric currents to the brain. The main effect of tDCS is to modulate cortical excitability depending on the polarity of the applied current. However, the underlying mechanism of neuromodulation is not well understood. A new generation of functional near infrared spectroscopy (fNIRS) systems is described that are miniaturized, portable, and include wearable sensors. These developments provide an opportunity to couple fNIRS with tDCS, consistent with a neuroergonomics approach for joint neuroimaging and neurostimulation investigations of cognition in complex tasks and in naturalistic conditions. The effects of tDCS on complex task performance and the use of fNIRS for monitoring cognitive workload during task performance are described. Also explained is how fNIRS + tDCS can be used simultaneously for assessing spatial working memory. Mobile optical brain imaging is a promising neuroimaging tool that has the potential to complement tDCS for realistic applications in natural settings.

Using Fiberless, Wearable fNIRS to Monitor Brain Activity in Real-world Cognitive Tasks

“…Given the need to bring functional imaging instruments outside the lab and given recent technological improvements, portable and wearable electroencephalography (EEG) and functional near infrared spectroscopy (fNIRS) systems have been developed [6][7][8][9][10][11] . One of the major advantages of fNIRS over EEG is its higher spatial resolution.…”

Functional Near Infrared Spectroscopy: Enabling routine functional brain imaging

“…(c) Battery operated and wireless unit allows untethered outdoor measurement during mobility studies. Modified with permission from [49]. (d) Hyperscanning fNIRS experiment simultaneously measuring brain activity in two people while they play a computer-based cooperation game side by side.…”

“…Measurements of the prefrontal cortex are particularly easy because of reduced interference from hair, but studies are and should measure from more brain regions. Recent reviews have addressed the application to emotional processing [46], mobility and aging [47], clinical psychology [48], psychiatry [7], integration with neuromodulation [49], and brain computer interfaces [50]. fNIRS complements fMRI because it permits rapid studies of larger numbers of subjects and more frequent longitudinal measurements of particular relevance for learning and treatment studies.…”

tDCS for Memory Enhancement: Analysis of the Speculative Aspects of Ethical Issues

“…Depending on whether the neural tissue being stimulated is below the anodal (negative current) or cathodal (positive current) electrode(s), neuronal excitability will be respectively increased or decreased (Coffman et al, 2014). tDCS promotes neuronal activity by increasing the concentration of excitatory neurotransmitters (e.g., glutamate) and growth factors (e.g., brain-derived neurotrophic factor, BDNF) in the synaptic cleft or by acting on the membrane potential (Levasseur-Moreau et al, 2013; Coffman et al, 2014; McKendrick et al, 2015). However, the mechanisms of action of tDCS likely involve different synaptic and non-synaptic effects on neurons and non-neuronal (e.g., glial) cells and tissues within the brain (Brunoni et al, 2011).…”