For the purpose of the

experiment, the manufacturer modified the device to automatically cycle between “on” blocks of 22 sec (specifically 10 sec on, then 2 sec off, then 10 sec on, due to constraints of the device) and “off” blocks of 22 sec. The device was connected via copper wires to adhesive nonferromagnetic electrodes (1.5-cm diameter contact area) that were placed on the participants’ right and left earlobes. Pre-MRI sensory threshold CES testing Participants received individualized subsensory current intensities to minimize the possibility that the current could be felt Inhibitors,research,lifescience,medical consciously in the scanner. This was done in order to avoid activation patterns associated with perception of stimulation, and also conforms to the way the device is used clinically. Testing was done using a forced-choice test outside of the scanner, to ensure that the participants could not guess if the device Inhibitors,research,lifescience,medical was on or off, at greater than chance level (see Supporting Information for details). CES safety testing in the MR environment Prior to the experiment, we tested the use of CES in the MRI scanner to ensure safety in terms of current, voltage, and temperature, and to verify that it did not produce any artifacts or field inhomogeneities in the MR image (see Supporting Information for details). SCH 900776 molecular weight Behavioral measurements To assess for any changes in

anxiety related to CES stimulation, Inhibitors,research,lifescience,medical participants completed the state portion of the State-Trait Anxiety Inventory (STAI) (Spielberger et al. 1983) before and after the fMRI scan. fMRI Participants were positioned in Inhibitors,research,lifescience,medical the scanner and the electrodes were applied to their earlobes. These were connected via long copper wires to the CES device, which the investigator operated in the scanner control room. Participants were instructed to: “keep your eyes closed for the duration of the scan Inhibitors,research,lifescience,medical but try not to fall asleep. You do not have to think about anything in particular.” After the scan, they were informally questioned about whether they could feel the stimulation during the scan. The experiment consisted of a blocked design in which six “on” blocks

of 22 sec alternated with six “off” blocks of 22 sec. There was 37.5 sec of baseline prior to the “on” and “off” cycles, and 33.5 sec of baseline following it. The total duration of each experimental run was 5 min and 35 sec. Participants completed one run each of the 0.5- and 100-Hz pulse frequencies, the order of which was counterbalanced between participants. Although the investigator the in the control room knew when the CES was cycling between “on” and “off” during the scan, the participants did not have any contact with him during each experimental run, and therefore could not be influenced implicitly or explicitly by the investigator’s knowledge. In this way, a control condition was built into the experiment in which there were blocks when the CES was off, but the participants did not know when this was occurring.