Effects of 8-week sensory electrical stimulation combined with motor training on EEG-EMG coherence and motor function in individuals with stroke

Abstract

The peripheral sensory system is critical to regulating motor plasticity and motor recovery. Peripheral electrical stimulation (ES) can generate constant and adequate sensory input to influence the excitability of the motor cortex. The aim of this proof of concept study was to assess whether ES prior to each hand function training session for eight weeks can better improve neuromuscular control and hand function in chronic stroke individuals and change electroencephalography-electromyography (EEG-EMG) coherence, as compared to the control (sham ES). We recruited twelve subjects and randomly assigned them into ES and control groups. Both groups received 20-minute hand function training twice a week, and the ES group received 40-minute ES on the median nerve of the affected side before each training session. The control group received sham ES. EEG, EMG and Fugl-Meyer Assessment (FMA) were collected at four different time points. The corticomuscular coherence (CMC) in the ES group at fourth weeks was significantly higher (p = 0.004) as compared to the control group. The notable increment of FMA at eight weeks and follow-up was found only in the ES group. The eight-week rehabilitation program that implemented peripheral ES sessions prior to function training has a potential to improve neuromuscular control and hand function in chronic stroke individuals.

Figure 1

CONSORT flow chart. Fifteen stroke patients were screened for eligibility and three of them were excluded (for weak thumb flexion (manual muscle test = 0,0,1/5)). Twelve subjects were randomly allocated and all of them completed the intervention session and the follow-up assessment. The data collected from all subjects were analyzed.

Figure 2

CMC of C2 electrode from typical subjects. CMC values before intervention (Pre), at the fourth week (4 wk), after completing 8 weeks of intervention (8 wk), and 4 weeks follow-up (f/u) for one subject in the ES group (dark line) and one subject in the control group (dashed line) were shown. The C2 electrode was chosen here because both subjects had right hemisphere stroke and C2 is the closet the right primary motor cortex hand area. The red line represents the critical threshold (0.0859) calculated by the equations described in Methods section. At the fourth week, the subject in the ES group had more area in beta band above the critical threshold, indicating the motor cortex had greater and physiologically meaningful functional connectivity with corresponding muscles.

Figure 3

CMC values between the ES and control groups. The data were presented as mean and SE. The CMC value in ES group at 4-wk had a trend to be higher than baseline (p = 0.046), 8-wk (p = 0.028), and follow-up (p = 0.028) while no significance difference can be found in control group. Moreover, the CMC value at 4-wk in ES group was significantly higher (p = 0.004) than that in control group. CMC: corticomuscular coherence; ES: electrical stimulation; 4 wk: 4^th week; 8 wk: 8^th week; f/u: follow-up. *Significance between groups.

Figure 4

FMA-UE score between the ES and control groups. The data were presented as mean and SE. The FMA-UE scores in ES group at both 8-wk and follow-up had the trend to be higher compared to baseline (p = 0.042 and p = 0.042.) There was no significant change with time in control group. No statistically significance can be found between groups. FMA-UE: Fugl-Meyer Assessment for Upper Extremity; ES: electrical stimulation; 4 wk: 4^th week; 8 wk: 8^th week; f/u: follow-up.