Aim: To investigate changes in neuromuscular function measured by high density electromyography (HD-EMG) before and after an associative brain computer interface (BCI) intervention within healthy participants and subacute stroke patients.
Method: Eleven healthy participants and four subacute stroke patients (three in the intervention group and one in the sham group) took part. For the healthy participants, the protocol consisted of two sessions: one intervention session and one sham session. For the stroke patients the BCI protocol consisted of 12 sessions, where HD-EMG was assessed in sessions 2 and 11.
During one session, a 64 channel HD-EMG matrix electrode placed on the extensor carpi radialis of the dominant/paretic arm was used to assess changes in neuromuscular function before and after the BCI session. In the initial HD-EMG measurements the maximal voluntary contraction (MVC) was found and used to calculate submaximal force levels. Three ramps of force contractions were performed at each submaximal force level: 20% and 50% MVC, respectively. The BCI session consisted of 30 ballistic extensions of the wrist in response to a visual cue combined with a peripheral electrical stimulation known as an associative BCI. After the BCI session the post HD-EMG measurements were performed.
Results: For the healthy participants no significant interaction or main effects were observed pre and post one BCI session for MVC, force CV, total number of motor units (MU), recruitment threshold (RT), or discharge rate (DR).
For the stroke patients they all had force improvements. The data for the DR varied. For the RT two from the intervention group and the one from the sham group overall seemed to increase between sessions. However, the data from the last stroke patient in the intervention group varied.
Conclusion: For healthy participants no significant changes were found suggesting that if neuromuscular changes contribute to the positive effects of an associative BCI intervention, they do not change significantly after only one session. All stroke patients got stronger and better at maintaining a steady force. The DR data for all stroke patients varied suggesting that the force improvements were not primarily due to improvements in DR. Independent of treatment three stroke patients had an increase in RT and improvements in MU firing behavior was observed. This pilot study is the first to assess changes in neuromuscular function in subacute stroke patients following four weeks of associative BCI intervention. However, more patients are needed to make more general conclusions.