Single-session tDCS over the dominant hemisphere affects contralateral spectral EEG power, but does not enhance neurofeedback-guided event-related desynchronization of the non-dominant hemisphere's sensorimotor rhythm

Abstract

Background and objectiveTranscranial direct current stimulation (tDCS) and neurofeedback-guided motor imagery (MI) have attracted considerable interest in neurorehabilitation, given their ability to influence neuroplasticity. As tDCS has been shown to modulate event-related desynchronization (ERD), the neural signature of motor imagery detected for neurofeedback, a combination of the techniques was recently proposed. One limitation of this approach is that the area targeted for stimulation is the same from which the signal for neurofeedback is acquired. As tDCS may interfere with proximal electroencephalographic (EEG) electrodes, in this study our aim was to test whether contralateral tDCS could have interhemispheric effects on the spectral power of the unstimulated hemisphere, possibly mediated by transcallosal connection, and whether such effects could be used to enhance ERD magnitudes. A contralateral stimulation approach would indeed facilitate co-registration, as the stimulation electrode would be far from the recording sites.MethodsTwenty right-handed healthy volunteers (aged 21 to 32) participated in the study: ten assigned to cathodal, ten to anodal versus sham stimulation. We applied stimulation over the dominant (left) hemisphere, and assessed ERD and spectral power over the non-dominant (right) hemisphere. The effect of tDCS was evaluated over time. Spectral power was assessed in theta, alpha and beta bands, under both rest and MI conditions, while ERD was evaluated in alpha and beta bands.ResultsTwo main findings emerged: (1) contralateral alpha-ERD was reduced after anodal (p = 0.0147), but not enhanced after cathodal tDCS; (2) both stimulations had remote effects on the spectral power of the contralateral hemisphere, particularly in theta and alpha (significant differences in the topographical t-value maps).ConclusionThe absence of contralateral cathodal ERD enhancement suggests that the protocol is not applicable in the context of MI training. Nevertheless, ERD results of anodal and spectral power results of both stimulations complement recent findings on the distant tDCS effects between functionally related areas.

The Tolerability and Efficacy of 4 mA Transcranial Direct Current Stimulation on Leg Muscle Fatigability

“…Additionally, the increased fatigability of the left (non-dominant) flexors in the 4 mA condition, which was over the dominant (left) M1, is also a novel finding. This suggests that tDCS of the dominant hemisphere may influence the non-dominant hemisphere, which has also been proposed elsewhere [40,51,52]. For example, the results of Mondini et al [51] indicated effects of tDCS on spectral EEG power on the side contralateral to stimulation and Park et al [52] found that stimulation of the left dorsolateral prefrontal cortex had diffuse effects on right hemisphere areas.…”

“…This suggests that tDCS of the dominant hemisphere may influence the non-dominant hemisphere, which has also been proposed elsewhere [40,51,52]. For example, the results of Mondini et al [51] indicated effects of tDCS on spectral EEG power on the side contralateral to stimulation and Park et al [52] found that stimulation of the left dorsolateral prefrontal cortex had diffuse effects on right hemisphere areas. The present finding also supports the idea of tDCS affecting interhemispheric cooperation of the primary motor cortices during motor performance [53] and may also help explain the promising findings of bilateral tDCS montages [23,54].…”

Different Effects of Transcranial Direct Current Stimulation on Leg Muscle Glucose Uptake Asymmetry in Two Women with Multiple Sclerosis

“…One reason might be that the relatively large tDCS electrode covered more areas than the M1 representation of the more-affected leg. Furthermore, it is also very likely that tDCS effects on the left hemisphere may influence the right hemisphere, consistent with previous studies [ 78 , 79 , 80 , 81 ]. For example, the results of Mondini et al [ 78 ] indicated effects of tDCS on spectral EEG power on the side contralateral to stimulation, and Park et al [ 79 ] found that stimulation of the left dorsolateral prefrontal cortex had diffuse effects on right hemisphere areas.…”

“…Furthermore, it is also very likely that tDCS effects on the left hemisphere may influence the right hemisphere, consistent with previous studies [ 78 , 79 , 80 , 81 ]. For example, the results of Mondini et al [ 78 ] indicated effects of tDCS on spectral EEG power on the side contralateral to stimulation, and Park et al [ 79 ] found that stimulation of the left dorsolateral prefrontal cortex had diffuse effects on right hemisphere areas. The present finding also supports the idea of tDCS affecting interhemispheric cooperation of the primary motor cortices during motor performance [ 79 ] and may also help explain the promising findings of this case study.…”

Differences in high-definition transcranial direct current stimulation over the motor hotspot versus the premotor cortex on motor network excitability

“…Despite large variability in the baseline MSE measurements, HD-tDCS over premotor cortex, as hypothesized, led to significant and more reliable changes in MSE than HD-tDCS over the motor hotspot. Given that HD-tDCS over premotor cortex led to more reliable changes in cortical excitability, it is likely this was also captured in the MSE changes found in both hemispheres (i..e., an enhancement of the excitability in the stimulated hemisphere associated with a decrease of the excitability in the contralateral hemisphere 53,54 ). In line with previous studies 33 , MSE and functional connectivity seemed to be complementary metrics: MSE may be more sensitive and able to capture local changes in the motor network whereas traditional rs-fMRI functional connectivity would capture more robust changes between distant brain areas.…”