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Transcranial magnetic stimulation (TMS) administration currently necessitates trained operators and equipment to hold the coil in place over specific brain targets [1], limiting its application in ambulatory, hospital or home settings. We have developed custom, individually-tailored TMS helmets that allow one to administer TMS in diverse settings where trained TMS operators are unavailable or the experiment or treatment involves movement such as ambulatory, extreme environments, or potentially at home. Here we overview how we constructed helmets that fix a TMS coil into position over a participant's motor hotspot (Fig. 1a and b) and describe its stepwise fabrication with video accompaniment (Supplemental Video). We also present withinand between-visit reliability resting motor thresholds (rMT) while wearing the helmets.

We are just beginning to understand how spaceflight may impact brain function. As NASA proceeds with plans to send astronauts to the Moon and commercial space travel interest increases, it is critical to understand how the human brain and peripheral nervous system respond to zero gravity. Here, we developed and refined head-worn transcranial magnetic stimulation (TMS) systems capable of reliably and quickly determining the amount of electromagnetism each individual needs to detect electromyographic (EMG) threshold levels in the thumb (called the resting motor threshold (rMT)). We then collected rMTs in 10 healthy adult participants in the laboratory at baseline, and subsequently at three time points onboard an airplane: (T1) pre-flight at Earth gravity, (T2) during zero gravity periods induced by parabolic flight and (T3) post-flight at Earth gravity. Overall, the subjects required 12.6% less electromagnetism applied to the brain to cause thumb muscle activation during weightlessness compared to Earth gravity, suggesting neurophysiological changes occur during brief periods of zero gravity. We discuss several candidate explanations for this finding, including upward shift of the brain within the skull, acute increases in cortical excitability, changes in intracranial pressure, and diffuse spinal or neuromuscular system effects. All of these possible explanations warrant further study. In summary, we documented neurophysiological changes during brief episodes of zero gravity and thus highlighting the need for further studies of human brain function in altered gravity conditions to optimally prepare for prolonged microgravity exposure during spaceflight.