Transcranial Brain Stimulation With Rapidly Spinning High-Field Permanent Magnets

Transcranial stimulation of the brain can be achieved by pulses of magnetic field delivered by a large electric coil. However, application of such pulses by rapidly moving small permanent magnets could offer several advantages in terms of ease of use, safety, multifocality, and portability. We have, therefore, developed a wearable brain stimulator consisting of small neodymium magnets that are spun at high speed by electric motors mounted on a cap. Here, we describe the operation of the stimulator and present initial evidence that its stimulation of the cerebral cortex produces physiological effects. We first physically tested the electromagnetic induction pattern produced by our stimulator compared with conventional transcranial magnetic stimulation. We then recorded the effects of stimulation of the primary motor cortical representation of the intrinsic muscles of the thumb including abductor pollicis brevis (APB). We studied these effects on spontaneously occurring electromyographic fasciculation potentials or spontaneous motor unit potentials (sMUPs) known to occur in healthy adult human subjects in resting APB, and compared them with the effects of sham stimulation. We found that while a single stimulus cannot elicit a motor-evoked potential, repetitive stimulation delivered by our stimulator modulates sMUP activity. This transcranial rotating permanent magnet stimulation could, therefore, produce neuromodulation at a single or multiple closely spaced cortical sites.