Feasibility of combining functional near-infrared spectroscopy with electroencephalography to identify chronic stroke responders to cerebellar transcranial direct current stimulation—a computational modeling and portable neuroimaging methodological study

Functional near-infrared spectroscopy (fNIRS) of posterolateral cerebellum and prefrontal cortex for fNIRS-driven cerebellar tES

“…This is relevant since contra-lesional ctDCS showed promise for improving standing balance performance in prior works [3], [4]. We also found a good general linear model (GLM) fit between the first principal component of the mean lobular ctDCS electric field strength with the latent variables of oxy-hemoglobin concentrations (HbO) from fNIRS and log10-transformed electroencephalogram (EEG) bandpower at the prefrontal cortex (PFC) and the sensorimotor cortex in the responders [2]. Here, a recent work found that the frontoparietal network is disproportionately expanded in the cerebellum compared to cortex [5].…”

“…In principal accordance, we conducted feasibility testing of fNIRS in young and healthy subjects to drive (phase amplitude coupling) cerebellar transcranial alternating current stimulation (ctACS) at 4Hz using infra-slow (0.01-0.10 Hz) PFC HbO activity. Here, fNIRS-driven 4Hz ctACS is expected to facilitate cerebellar brain inhibition [6] better than ctDCS that we measured using fNIRS [2].…”

“…We found [2] a linear relationship between electric field distribution and the HbO response using GLM analysis of variance (ANOVA) for the ctDCS montages where the montage for the dentate nuclei targeted Crus I/II more than the ctDCS montage targeting lower limb representations. In this study, we optimized the ctDCS/ctACS electrode montage for non-motor representation, i.e., right lobules VI-CrusI/II-VIIb, using EEG locations -Fig.…”

“…In this study, fNIRS was conducted using NIRSPORT 2 (NIRx, USA) where our optode montage consisted of 12 long-separation (~3.5cm) sources, 3 longseparation detectors, and 3 short-separation (<1cm) detectors that covered PFC, and CER. This long-separation optode montage was selected to match our low-channel count montage (Octamon+, Artinis Medical Systems, Netherlands) used in stroke study where fNIRS sources were positioned at AF7, AF3, AF8, AF4, CP4, FC4, CP3, and FC3, and the two detectors were placed at the Cz and FPz with a source-detector distance of around 35mm [2]. For CER, fNIRS sources were positioned at the PO7, PO9, PO8, and PO10, and the detector was placed at Iz based on fNIRS Optodes' Location Decider (fOLD) [18].…”

“…Furthermore, cerebellum supplied by the cerebellar arteries is spared along with the cerebello-cerebral connectivity to the medial part of the frontal lobe when deep territory of the MCA is not involved. Such stroke survivors have been found to be mostly responsive to cerebellar transcranial direct current stimulation (ctDCS) for standing balance rehabilitation [1] where functional near-infrared spectroscopy (fNIRS) can be used to identify responders [2]. This is relevant since contra-lesional ctDCS showed promise for improving standing balance performance in prior works [3], [4].…”