Task-Related Hemodynamic Changes Induced by High-Definition Transcranial Direct Current Stimulation in Chronic Stroke Patients: An Uncontrolled Pilot fNIRS Study

Abstract

High-definition transcranial direct current stimulation (HD-tDCS) has recently been proposed as a tDCS approach that can be used on a specific cortical region without causing undesirable stimulation effects. In this uncontrolled pilot study, the cortical hemodynamic changes caused by HD-tDCS applied over the ipsilesional motor cortical area were investigated in 26 stroke patients. HD-tDCS using one anodal and four cathodal electrodes at 1 mA was administered for 20 min to C3 or C4 in four daily sessions. Cortical activation was measured as changes in oxyhemoglobin (oxyHb) concentration, as found using a functional near-infrared spectroscopy (fNIRS) system during the finger tapping task (FTT) with the affected hand before and after HD-tDCS. Motor-evoked potential and upper extremity functions were also measured before (T0) and after the intervention (T1). A group statistical parametric mapping analysis showed that the oxyHb concentration increased during the FTT in both the affected and unaffected hemispheres before HD-tDCS. After HD-tDCS, the oxyHb concentration increased only in the affected hemisphere. In a time series analysis, the mean and integral oxyHb concentration during the FTT showed a noticeable decrease in the channel closest to the hand motor hotspot (hMHS) in the affected hemisphere after HD-tDCS compared with before HD-tDCS, in accordance with an improvement in the function of the affected upper extremity. These results suggest that HD-tDCS might be helpful to rebalance interhemispheric cortical activity and to reduce the hemodynamic burden on the affected hemisphere during hand motor tasks. Noticeable changes in the area adjacent to the affected hMHS may imply that personalized HD-tDCS electrode placement is needed to match each patient's individual hMHS location.

Keywords: functional near-infrared spectroscopy; high-definition transcranial direct stimulation; oxyhemoglobin concentration; stroke; upper extremity function.

Figure 1

Study design. (A) Experimental paradigm. (B) fNIRS measurement during the FTT. A star appeared on the black screen for 600 ms, and then an empty black screen appeared for 400 ms after the star disappeared. Each subject pushed the corresponding buttons using fingers on the affected side. (C) Arrangement of fNIRS optodes and HD-tDCS electrodes. fNIRS, functional near-infrared spectroscopy; FTT, finger tapping task; HD-tDCS, high-definition transcranial direct current stimulation; Nz, nasion; Iz, inion; LPA, left pre-auricular; RPA, right pre-auricular.

Figure 2

Average cortical activation maps, as analyzed using the NIRS-SPM software during the FTT with the affected hand before and after HD-tDCS intervention. The white dotted areas indicate the MThe green dotted areas indicate the SMA. The purple dotted areas indicate the PMC. The orange dotted areas indicate the SAt T0, the cortical oxyHb concentration increased during the FTT in both the affected and unaffected hemispheres. At T1, the overall cortical activation was decreased and most of the activation was shifted to the affected hemisphere. FTT, finger tapping task; T0, before the intervention; T1, after the intervention; M1, primary motor cortex; SMA, supplementary motor area; PMC, premotor cortex; S1, primary somatosensory cortex; oxyHb, oxyhemoglobin.

Figure 3

(A) Location of the fNIRS channels. The red rhombi represent the individual hMHS locations. The anode electrode was placed on the ipsilesional hemisphere of each participant (C3 or C4). When the anode was on C3, the cathodes were placed on C1, C5, FC3, and CPWhen the anode was on C4, the cathodes were placed on C2, C6, FC4, and CPIn this figure, all patients were assumed to have the right-sided lesions, so the location of the fNIRS channels, optodes, HD-tDCS electrodes, and individual hMHS locations are expressed in the right hemisphere. (B) Results of time series oxyHb concentration changes in the affected motor area in each fNIRS channel during the FTT. The red dotted and solid lines represent the oxyHb concentration at T0 and T1, respectively. The blue dotted and solid lines represent the deoxyHb concentration at T0 and T1, respectively. The colored background represents the standard error. In channel 32, the oxyHb concentration was significantly decreased at T1 compared with T0. hMHS, hand motor hotspot; oxyHb, oxyhemoglobin; deoxyHb, deoxyhemoglobin; T0, before intervention; T1, after intervention; FTT, finger tapping task.