5 sec window prior to the start of the next trial, for a total of 3.5 sec per trial. Each condition was randomized and performed in six blocks of 120 trials with each block lasting approximately 5 min. The order of the conditions was counterbalanced across each block and all subjects performed the same six blocks in sequential order. Stimuli Visual stimuli consisted of a centrally presented horizontal bar (6 cm
wide), which raised to varying heights on a computer monitor positioned 50 cm in front of the AC220 purchase subject and represented different visual amplitudes. Vibrotactile Inhibitors,research,lifescience,medical stimuli consisted of discrete vibrations delivered by a custom made vibrotactile device applied to the volar surface of the left index finger. Vibrotactile stimulation was controlled Inhibitors,research,lifescience,medical by converting digitally generated waveforms to an analog signal (DAQCard 6024E; National Instruments, Austin, TX) and then amplifying the signal (Bryston 2BLP, Peterborough, Ontario, Canada) using a custom program written in LabVIEW (version 8.5; National Instruments). Varying the amplitude of the driving voltage to the vibrotactile Inhibitors,research,lifescience,medical device produced proportional changes in vibration of the device on the finger. The amplitude of each discrete vibration was constant within a trial
and varied randomly between trials. The average stimulus amplitude across all trials including a tactile stimulus did not differ between the experimental conditions. The frequency of the vibration was held constant at 25 Hz. Participants received 70 db whitenoise (Stim2; Neuroscan, Compumedics USA, Charlotte, NC) throughout the training session and the experiment to prevent auditory perception of the vibrotactile Inhibitors,research,lifescience,medical stimulus. Data acquisition and recording parameters EEG
data were recorded from 64 electrode sites (64-channel Quick-Cap, Neuroscan, Compumedics USA) in accordance with the international 10–20 system for electrode placement, and referenced to the linked mastoids (impedance <5 kOhms). EEG data were amplified (20,000×), filtered (DC-200 Hz), Inhibitors,research,lifescience,medical and digitized at 500 Hz (Neuroscan 4.3, Compumedics USA) before being saved for subsequent analysis. Individual traces were visually inspected for artifacts (i.e., blinks, eye movements, or muscle contractions) and any contaminated epochs were eliminated before averaging. On Idoxuridine average a minimum of at least 80 trials per condition were analyzed for each participant. Event-related potentials were averaged to the onset of each stimulus relative to a 100-msec pre-stimulus baseline. Somatosensory ERPs were measured from individual participant averages for each task condition. Mean ERP amplitudes and latencies were computed for each subject within specified time windows selected around the post stimulus latencies of early somatosensory ERP components: P50 (40–70 msec), P100 (90–125 msec).