After consenting to participate in the study, participants will fill out the medical screening questionnaire. Two days prior to their scheduled experimental trial, participants will be given an activity wrist monitor and instructed that their daily schedules should include a minimum of seven hours of sleep per night between the hours of 2300 and 0600. Also during this time participants will receive training on all four performance tasks to be utilized in the study. Participants will be trained to asymptote on the performance tasks to guard against learning effects during experimental testing. Therefore, more training may be administered if necessary.

Participants will also become familiarized with the subjective questionnaires. On the day of their experimental trial, participants will be required to awaken at 0600 and perform their daily activities as normal. They will be instructed to not consume any caffeine or central nervous system (CNS)-altering medications/substances on the experimental test day. Each participant will arrive at the test facility at 1530 hours. Upon arrival, their activity data will be analyzed to ensure that proper sleep cycles were maintained. Starting at 1600 hours, participants will complete one session of the vigilance task (30 minutes), one session of the working memory task (20 minutes), one session of the PVT task (10 minutes), one session of the Multi-attribute task battery (MATB) task (20 minutes), and fill out the Profiles of Mood States (POMS-B), Visual Analog Scale (VAS), and side–effects questionnaires. Afterwards, participants will be provided a break of approximately 90 minutes where they can talk, watch TV, walk, read, or play video games. The second session will begin at 1900 hours. Participants will be given active or sham tVNS depending on their experimental group. These procedures will be repeated every three hours with the final session occurring at 1600 the following day (36 hours continuous wakefulness).

RESULTS:
High levels of performance at all times is a requirement for success in both military and space exploration populations. Non-invasive vagal nerve stimulation has been shown to augment cognitive performance such as learning, memory retention, attention, and arousal. The results from this research will help determine the feasibility of tVNS to limit the effects of fatigue stress on NASA and military operators. While there is no substitute for adequate sleep, this may substantially reduce errors and attention lapses caused by increased fatigue when rest is not an option.