Preliminary study of steerable pulsed transcranial electrical stimulation (TES) of motor cortex in humans

Electrical stimulation of neurons in the brain is used routinely in neuroscience and has numerous clinical applications. In contrast to invasive neural stimulation using invasive probes inserted in the brain, transcranial electrical stimulation (TES) is a safe and non-surgical neuromodulation modality. TES is generally performed using individually positioned large electrodes, which limits its precision and control. In this paper, we utilize high density surface electrode arrays to precisely control the location of TES in the human motor cortex. Current pulses of 100 µs duration and 50 to 150 mA amplitude were injected across electrodes chosen from within an array of 64 electrodes (7 mm pitch) placed above the motor cortex while recording high resolution electromyogrpahic (EMG) activity in the contralateral arm and hand muscles. Motor evoked potential (MEP) amplitude quantifies the changes in activity across the different muscles as a function of the stimulation electrode position. A map of motor responses to TES for six muscle groups in the arm is presented, showing that moving the injected electric field by sub-cm distances changes the activation profile of arm and hand muscles. This work demonstrates the potential of TES to elicit precisely controlled motor activity.Clinical relevance-Precision TES could replace invasive stimulation in some clinical applications, as well as improve the precision of intraoperative monitoring of muscle function.