Gurmeen Kaur, MBBS
Bundy DT, Souders L, Baranyai K, Leonard L, Schalk G, Coker R, et al. Contralesional Brain–Computer Interface Control of a Powered Exoskeleton for Motor Recovery in Chronic Stroke Survivors. Stroke. 2017
Brain computer interfaces (BCIs) are defined as systems which take biological signal from a person and predict some abstract aspect of the person’s cognitive state. The goal of the BCI technology is to give severely paralyzed people a way to communicate.
While BCIs can use several input-signals, including EEG, EMG, and fMRIs, the BCI technology developed for chronic stroke rehabilitation has been focused on demonstrating motor improvement with the use of EEG input. Recent studies have shown that BCI-controlled orthoses or functional electric stimulators can lead to improvements in motor function in chronic stroke survivors.
In this study, the authors recruited 10 subjects with chronic hemiparesis involving the upper extremity for a home-based BCI powered exoskeleton. Previous experimenters had used EEG signals derived from “perilesional” cortex, contralateral to the arm involvement—which means the area next to that affected by the stroke. The problem with use of perilesional cortex was that if the infarct size is large, with extensive cortical damage, the perilesional cortex was not able to produce sufficient EEG signal to power the exoskeleton. To overcome this, the authors used “contralesional” cortex, ipsilateral to the affected arm. This is the first study to look at the use of the unaffected hemicortex in chronic stroke recovery and aimed to see if plasticity could be triggered.
The exoskeleton is a sophisticated BCI system which is powered by commercial EEG amplifier and active electrodes. EEG output from the contralesional cortex was recorded when the patient moved the unaffected limb, attempted to imagine moving the affected limb and imagined moving both limbs together. This output was then translated into actual hand movement aided by the manual exoskeleton, which opened and closed the patient’s hand in a 3-finger pinch grip (1 degree of freedom). Spectral power changes were used to provide visual and proprioceptive feedback to the sensory cortex, to close the loop.
The primary outcome measure was the Action Research Arm Test (ARAT). Patients were instructed to use the BCI system on a minimum of 5 days per week. They were using the system both at rest and during active attempted movement of the affected limb. Since this was a home-based study, 2-week lab follow ups were done to assess changes over a total of 12 weeks.
The study concluded that patients had a statistically significant mean ARAT increase of 6.2 points. To understand the significance of this improvement, it is important to understand that 5.7 points has been estimated to represent the minimal clinically important difference in chronic stroke survivors. Six of the 10 patients enrolled had ARAT improvements of more than 5.7 points. There was a positive association between ARAT change and change in the EEG modulation per run of the BCI task at the location and frequency used for BCI control and in a site in the contralateral motor cortex (BCI control feature: Spearman r=0.48, P=0.16, contralateral motor cortex: Spearman r=0.62, P=0.06).
Meaningful clinical improvement with the use of a BCI powered rehabilitation program for stroke recovery, especially in a home-based setting, shows significant promise for building future BCI-driven rehab programs aimed at triggering cortical plasticity, and we will be witnessing a paradigm shift in poststroke motor recovery in the years to come!