Effects of Increasing Neuromuscular Electrical Stimulation Current Intensity on Cortical Sensorimotor Network Activation: A Time Domain fNIRS Study

Abstract

Neuroimaging studies have shown neuromuscular electrical stimulation (NMES)-evoked movements activate regions of the cortical sensorimotor network, including the primary sensorimotor cortex (SMC), premotor cortex (PMC), supplementary motor area (SMA), and secondary somatosensory area (S2), as well as regions of the prefrontal cortex (PFC) known to be involved in pain processing. The aim of this study, on nine healthy subjects, was to compare the cortical network activation profile and pain ratings during NMES of the right forearm wrist extensor muscles at increasing current intensities up to and slightly over the individual maximal tolerated intensity (MTI), and with reference to voluntary (VOL) wrist extension movements. By exploiting the capability of the multi-channel time domain functional near-infrared spectroscopy technique to relate depth information to the photon time-of-flight, the cortical and superficial oxygenated (O2Hb) and deoxygenated (HHb) hemoglobin concentrations were estimated. The O2Hb and HHb maps obtained using the General Linear Model (NIRS-SPM) analysis method, showed that the VOL and NMES-evoked movements significantly increased activation (i.e., increase in O2Hb and corresponding decrease in HHb) in the cortical layer of the contralateral sensorimotor network (SMC, PMC/SMA, and S2). However, the level and area of contralateral sensorimotor network (including PFC) activation was significantly greater for NMES than VOL. Furthermore, there was greater bilateral sensorimotor network activation with the high NMES current intensities which corresponded with increased pain ratings. In conclusion, our findings suggest that greater bilateral sensorimotor network activation profile with high NMES current intensities could be in part attributable to increased attentional/pain processing and to increased bilateral sensorimotor integration in these cortical regions.

Focal Hemodynamic Responses in the Stimulated Hemisphere During High-Definition Transcranial Direct Current Stimulation

“…In our previous pilot study using a two channel time‐resolved fNIRS device and modeling methods to disentangle scalp from cerebral hemodynamic changes , we showed that during anodal HD‐tDCS a greater portion of the fNIRS O 2 Hb signals were derived from the scalp level skin blood flow changes in close proximity to the anode of the 4 × 1 electrode montage with a smaller proportion from the intracranial (cerebral) layer. In the present study, our findings of the grater spatial distribution of O 2 Hb int values within than outside the boundary of the 4 × 1 electrodes ( L in > L out ROI) were representing a direct tissue effect of the scalp‐applied HD‐tDCS electric field stimulating scalp afferents and skin blood flow changes with a smaller proportion from the intracranial (cerebral) layer neurovascular coupling.…”

Different mechanosensory stimulations of the lower back elicit specific changes in hemodynamics and oxygenation in cortical sensorimotor areas—AfNIRSstudy

“…This is in line with the current evidence from literature (Tachtsidis & Scholkmann, ). Interestingly, scalp blood flow changes (especially in the [O 2 Hb] signal) have been also observed during stimulations of sensorimotor areas due to nonpainful and painful electrical muscle stimulations (Muthalib et al., ). It could be shown that these task‐related scalp blood flow changes took place and that correcting for them is necessary.…”

Effects of combined treatment with blood flow restriction and low‐intensity electrical stimulation on diabetes mellitus‐associated muscle atrophy in rats

“…These observations suggest that ES could be an effective therapeutic intervention for diabetes‐associated muscle atrophy, as well as for disuse‐ and inflammation‐induced muscle atrophy. However, ES causes severe pain and discomfort, but the levels of pain and discomfort depend on current intensity . Therefore, because high‐intensity ES induces severe pain while attempting to induce strong muscle contraction, it is necessary to develop new therapeutic treatments using ES to prevent muscle atrophy in order to avoid severe pain and discomfort.…”

“…In addition, low‐intensity resistance exercise during Bfr could reduce the risk of the progression of microvascular complications without increasing blood pressure . Low‐intensity ES can be used instead of low‐intensity resistance exercise and, if the current intensity is maintained at a low level, severe pain and discomfort can be avoided . Therefore, the combination of Bfr and low‐intensity ES may be an effective therapeutic treatment to prevent diabetes‐associated muscle atrophy by inhibiting the decrease in protein synthesis, even at low intensity ES.…”