Remote targeted electrical stimulation

The ability to generate electric fields in deep tissues remotely, without surgically implanting electrodes, could transform diagnoses and treatments of nervous system disorders. Here, we show that focal electrostimulation effects can be elicited remotely by combining two noninvasive forms of energies--magnetic and focused ultrasonic fields. The approach, based in the Lorentz equation and referred to as Lstim, electrically stimulates specified tissue targets with the precision of deep brain or spinal cord stimulation, but does not require electrode implantation. Lstim potentiated the responses of human nerves, enhancing the neuromodulatory effects of ultrasound by 74% on average. The effects showed a double dissociation--a significant and substantial increase in nociceptive responses, yet a significant reduction in tactile responses. In line with the Lorentz equation, Lstim was only observed when nerves were oriented perpendicularly to the magnetic and ultrasonic fields. A sham condition showed no effects. Both the ultrasonic and the induced electric fields were well below the respective safety indices, and no detrimental effects were detected. Lstim uniquely integrates noninvasiveness, sharp focus, and the efficacy of electrical stimulation. The approach has the potential to provide a noninvasive tool to dissect brain function in humans and to diagnose the neural circuits involved in nervous system disorders. Moreover, this effect should be taken into account when ultrasound is applied inside MRI.