Waveguard cap

EEG data were obtained in 2 separate laboratories for stroke participants and healthy adults, respectively. Acquisition and analyses were identical, except for minor differences that were corrected during data preprocessing to ensure that all data were identical prior to analysis. For all participants, 3 minutes of resting EEG was acquired using an ASA-lab EEG system with 64 channel Waveguard cap (ANT Neuro, Enschede, Netherlands). Signals were sampled at 2048 Hz, amplified 20×, online filtered (stroke participants: 1-45 Hz; healthy adults: DC-553 Hz), and online referenced to CPz (stroke participants) or common average (healthy adults). Signal impedance was kept to <5 kΩ using EEG conductive gel. Participants were seated comfortably in a quiet room during data recording. Prior to recording data, participants were asked to relax, keep their eyes open and look straight ahead at a fixation point positioned at eye level, and refrain from speaking or moving and not to actively engage in any cognitive or mental tasks.

A Micromed System Plus (Micromed, Mogliano, Italy) with Ag/AgCl electrodes were used to record EEG at 60 standard locations according to the international 10-10 system using a 64 channel WaveGuard cap (ANT Neuro, Netherlands). Cz was used for referencing during online acquisition, and AFz was used as the ground. Vertical and horizontal electrooculogram (EOG), respiration (RESP), electrocardiogram (ECG) and pulse oximetry (PO) were recorded using bipolar channels. O1, O2, PO7, and PO8 were omitted from the EEG montage to make recording channels available for physiological data. For ECG, one electrode was placed below the right mid-clavicle and the other was placed on a lower left rib, producing a high-amplitude R-wave to facilitate automatic peak detection. EEG, EOG, RESP, ECG, and PO were digitized online using a sampling rate of 1024 Hz and online high-pass filter of 0.008 Hz. Electrode impedances for the EEG channels were stabilized below 5 kΩ before recordings commenced. RESP and PO data were not considered for the present report.

Neural activity and kinematic measures were simultaneously recorded during the whole experiment. Electroencephalographic activity was recorded (EEG; µV) using a high-density 64-channel Waveguard cap (ANT Neuro, Enschede, Netherlands). EEG electrodes were arranged according to the International 10-20 System (Jasper, 1958) . Data were amplified with a TMSi Refa Ext amplifier (ANT Neuro, Enschede, Netherlands), digitized at 1024 Hz, and band-pass filtered from 0.1 to 500 Hz. Impedance was kept below 5 kΩ. During recordings, the Fz electrode was used as a reference. Kinematic measures were obtained from the automatic recordings of the robotic device and included end-effector position and velocity (along the x and y axes) and exerted forces (along x, y and z axes). Kinematic data were sampled at 200 Hz and stored for off-line analysis. The two signals were synchronized by a TTL pulse signal emitted by the robotic device in correspondence of each visual cue and transmitted to the EEG recording system via a BNC cable.

All stimuli were presented using a gamma corrected ViewPixx 3D display (VPixx technologies, Canada) driven by a Mac Pro. Binocular separation with minimal crosstalk was achieved by synchronizing the refresh rate of the display with the toggling of a pair of Nvidia stereo shutter goggles using an infra-red signal. Monitor refresh rate was set to 120Hz, meaning that each eye was updated at 60Hz (every 16.67 msec). Display resolution was set to 1920 X 1080 pixels. A single pixel subtended 0.027° of visual angle (1.63 arc min) when viewed from 57 cm. The mean luminance of the display viewed through the shutter goggles was 26 cd/m 2 . EEG signals were recorded from 64 electrodes distributed across the scalp according to the 10/20 EEG system (Chatrian et al., 1985) (link) in a WaveGuard cap (ANT Neuro, Netherlands). We monitored eye blinks with an electrooculogram, which consisted of bipolar electrodes placed above the eyebrow and atop of the cheek on the left side of the participant's face. Stimulus-contingent triggers were sent from the ViewPixx display to the amplifier using a parallel cable. Signals were amplified and digitized using a PC with the ASAlab software (ANT Neuro, Netherlands). All EEG data were imported into MATLAB (Mathworks, MA, USA) and analysed offline.