Does feedback based on FES-evoked nociceptive withdrawal reflex condition event-related desynchronization? An exploratory study with brain-computer interfaces.

Introduction. Event-related desynchronization (ERD) is used in brain-computer interfaces (BCI) to detect the user's motor intention (MI) and convert it into a command for an actuator to provide sensory feedback or mobility, for example by means of functional electrical stimulation (FES). Recent studies have proposed to evoke the nociceptive withdrawal reflex (NWR) using FES, in order to evoke synergistic movements of the lower limb and to facilitate the gait rehabilitation of stroke patients. The use of NWR to provide sensorimotor feedback in ERD-based BCI is novel; thererfore, the conditioning effect that nociceptive stimuli might have on MI is still unknown. Objetive. To assess the ERD produced during the MI after FES-evoked NWR, in order to evaluate if nociceptive stimuli condition subsequent ERDs. Methods. Data from 528 electroencephalography trials of 8 healthy volunteers were recorded and analyzed. Volunteers used an ERD-based BCI, which provided two types of feedback: intrisic by the FES-evoked NWR and extrinsic by virtual reality. The electromyogram of the tibialis anterior muscle was also recorded. The main outcome variables were the normalized root mean square of the evoked electromyogram (RMS norm ), the average electroencephalogram amplitude at the ERD frequency during MI (AMI) and the percentage decrease of AMI relative to rest (ERD%) at the first MI subsequent to the activation of the BCI. Results. No evidence of changes of the RMS norm on both the AMI (p = 0.663) and the ERD% (p = 0.252) of the subsequent MI was detected. A main effect of the type of feedback was found in the subsequent AMI (p < 0.001), with intrinsic feedback resulting in a larger AMI. Conclusions. No evidence of ERD conditioning was observed using BCI feedback based on FES-evoked NWR . Significance. FES-evoked NWR could constitute a potential feedback modality in an ERD-based BCI to facilitate motor recovery of stroke people.