The optimal delivery of a Brain Computer Interface intervention for people with stroke.

Each participant will receive three different conditions, two interventions, and one control, on three different days, 7 days apart (in a randomised order). Participants will be blinded to this order. At the start of each session, electroencephalography (EEG) will be recorded using an EEG cap, while participants perform 50 repetitions of active ankle dorsiflexion of their affected leg, in time with a visual cue. The visual cue is a moving cursor on a computer screen which prompts the participant to prepare and then move their ankle. The EEG is then analysed and the peak negativity of the movement related cortical potential (MRCP) is determined. This timing is then used to inform the timing of one of the interventions. For the two interventions, the participant will complete 50 repetitions of cued active ankle dorsiflexion of the affected leg. During each repetition of ankle dorsiflexion, a single pulse of electrical stimulation (pulse width 1ms) will be delivered to the deep branch of the common peroneal nerve (via two surface electrodes placed approximately 2-5cm anterior and inferior to the head of the fibula). The intensity of the electrical stimulation will be set to the level required to produce a palpable twitch in the tibialis anterior tendon (device intensity range 0-100mA). For the first intervention, each pulse of electrical stimulation will be timed to arrive in the motor cortex at the point of peak negativity of the MRCP. This timing is set from the pre-recorded MRCP, and therefore is an 'off-line' version of a Brain Computer Interface (comprised of an EEG recording, a computer analysing the EEG and triggering the stimulator, and an electrical stimulation unit). For the second intervention, each pulse of electrical stimulation will be timed to arrive in the motor cortex at the time the visual cue is given (to move the affected leg). The intervention takes approximately 15 minutes, with additional time required for setting up the electrical stimulation. Sessions will be delivered by a trained research assistant. The parameters of intervention delivery and any clinical observations concerning the participants engagement and adherence to the intervention will be recorded on data collections sheets.