Comparison of SMR and SCP training employing a newly developed discrete-trial based biofeedback system
Background Operant conditioning of one’s slow cortical potential (SCP) or sensorimotor rhythm (SMR) can be used to control epilepsy or to manipulate external devices, as applied in BCI (Brain-Computer Interface). To be practical, a BCI-system should use as less channels as possible. For this purpose, a wireless biofeedback system was developed that allows feedback of a single EEG-channel in discrete trials. The commonly accepted view that both the SCP and SMR are a reflection of central arousal suggests a functional relationship between SCP and SMR networks. Methods A training was performed that aimed to teach 19 participants to control their SCP (n=9) or SMR (n=10) over vertex. Participants received 20 neurofeedback sessions, each comprising of 96 trials in which they had to decrease cortical arousal (SCP positivity/SMR enhancement) and 64 trials in which they had to increase cortical arousal (SCP negativity/SMR suppression). In a trial, participants were required to exceed an individual threshold level of the feedback parameter relative to a 500 ms pre-feedback baseline and hold this level for 2 seconds (SCP) or 0.5 seconds (SMR) in order to obtain reinforcement. Results Overall, 10 of the total of 19 participants achieved control over their EEG. In the SCP-trained group, 4 out of 9 participants were able to increase the differentiation between their SCP responses on positivity- required vs. negativity-required trials over the course of the experiment. Improvements in control over the SMR in suppression-required and enhancement-required trials were acquired by respectively 3 and 4 of the 10 SMR-trained participants. These SMR-trained responders did not show differentiation between their SMR responses in enhancement-required vs. suppression-required trials. Interestingly, the SMR responders did show a differentiation in their SCP response while trained on SMR. Conclusions It can be concluded from this experiment that, with the proposed method, a number of the participants are able to acquire control over their SCP or SMR. For SMR, however, bidirectional control is very difficult to achieve with the present training procedure. Furthermore, SCP positivity and SMR enhancement are easier to learn compared to their counterparts. The observed SCP differentiation while training SMR and absence of equivalent SMR changes while training SCP suggest that SMR training modulates the central arousal system, whereas SCP training invokes local effects.