D360 amplifier

Using Ag/AgCl surface electrodes via D360 amplifiers (Digitimer, UK), motor evoked potentials (MEP's, filtered between 3 and 3000 Hz) were recorded over three muscles involved in a finger extension (Darling and Cole, 1990 (link)) (Figure 1C), the FDI, thumb opponent (THU) and extensor digitorum (EXT) muscles. Signals were sampled at 10 kHz and stored via the CED1401. MEP amplitude and the level of background EMG (Thompson et al., 1991 (link)) (area/time from −80 to −10 ms relative to the TMS-pulse) were calculated with customized MatLab programmes (The Mathworks, USA). This procedure was repeated in Experiments 3 and 4.

MEPs, EMG activity and SP evoked by stimulation were recorded with surface electrodes placed in the belly-tendon position with Digitimer Ltd. D360 amplifiers (gain 250, bandpass 3–3000 Hz). The first dorsal interosseous was the target muscle whose activity was recorded and sent to a CED Ltd. 1401mkII unit 1 (sampling at 10 kHz and storing signals); we also recorded activity from the extensor indicis. Finger movements were monitored using an electrogoniometer (S100) and finger force using a dynamometer (P200), both connected to a K800 amplifier (Biometrics Ltd.) and sent to CED1401mkII unit 1 for sampling (10 kHz) and storage. In parallel, the force signal was sent to another CED1401mkII (unit 2) run with Sequencer. Sequencer (sampling at 100 kHz) ran an algorithm (previously described in detail and validated^{8 (link)}) to trigger TMS at MVC peak plateaus and percutaneous nerve stimulation in the resting muscle; the transistor-transistor logic (TTL) triggers from CED1401mkII unit 2 to the stimulators were also sent to CED1401mkII unit 1 as TTL markers to facilitate offline data processing.

Each subject was evaluated in a comfortable prone position. Surface electromyography (EMG) was recorded from the right soleus muscle by using adhesive electrodes (Ambu Blue Sensor SnapTab). The active electrode was located over the muscle belly and the reference electrode was located over the Achilles tendon (ground was attached over the proximal portion of the peroneal bone). The EMG was amplified (gain x1000) and band-pass filtered (1Hz to 3 kHz) by Digitimer D360 amplifiers (Digitimer Ltd., Welwyn Garden City, Herts, UK). Signals were recorded at a sampling rate of 10 kHz and stored on the computer for later analysis by Signal software (Cambridge Electronic Design Ltd., Cambridge, UK) through a power 1401 data acquisition interface (Cambridge Electronic Design Ltd., Cambridge, UK). All assessments were performed with the muscle at rest. The EMG background was continuously monitored and traces showing EMG activity were discarded online or offline. To obtain the H reflex, we used a constant current stimulator (DS7A, Digitimer, Welwyn, UK) to apply stimuli of 1 ms pulse width to the tibial nerve. For tibial nerve stimulation, the active electrode was placed in the popliteal fossa (cathodal current) and reference electrode was attached on the skin over the patella through adhesive electrodes (Ambu Blue Sensor SnapTab).