Considerations on the Individualization of Motor Imagery Neurofeedback Training

Motor imagery (MI), the mental rehearsal of a movement task, is known to activate similar brain areas to the ones related to actual motor execution. Based on this, MI has been used in many brain-computer interface (BCI) applications, ranging from motor rehabilitation to the actual control of external hardware and other devices. Although great improvement has been made in the field, MI-BCIs still face several issues that limit their applicability to the clinical environment. The aim of this work was to improve on the understanding of one of these issues - namely, the inter and intra-subject variability regarding the electroencephalography (EEG) signals produced by MI tasks. EEG data from 10 healthy subjects who underwent 12 hands-MI sessions, without any feedback, were collected. Differently than most current studies in the field, we screened our analysis into small frequency intervals, from 526 Hz, at 4 Hz steps. We then computed how often a given (electrode, frequency interval) pair was optimal for BCI classification, across all sessions, attempting to identify features that would maximize reproducibility. Although similar electrodes are most recurrent across all subjects, each participant displayed their own particularities. Also, these individual patterns did not necessarily reflect the traditional locations over the primary sensorimotor cortex of most EEG-MI studies. Furthermore, our classification results suggested that identifying the best spectral intervals, and not just electrodes, is crucial for improving results. Given the reduced number of existing training protocols supporting individualization, we emphasize that considering subjects' particularities is essential.