UC Berkeley

1. Movements of either the contralateral or ipsilateral arm produce changes in neural activity insensorimotor cortex as well as subcortical structures. To better understand what information is encoded by the ipsilateral arm, and if this information could be used in more applied settings (i.e., deep brain stimulation), we conducted two experiments utilizing patients who have intracranial recordings for clinical purposes. In the first study we examined patients with intracranial grids implanted in either the left or the right hemisphere. Implementing a crossvalidated kinematic encoding model, we found stronger bilateral encoding in the left hemisphere, an effect that was present during preparation and was amplified during execution. Consistent with this asymmetry, we also observed better across-arm generalization in the left hemisphere. The more extensive bilateral encoding in the left hemisphere adds a new perspective to the pervasive neuropsychological finding that the left hemisphere plays a dominant role in praxis. In the second study we examined neural recordings from patients with a deep brain stimulation lead targeting the subthalamic nucleus as well as a cortical strip while they made repetitive hand movements. We fit the continuous EMG to the neural activity using a cross-validated encoding model and found that electrodes in the subthalamic region encode both hands equally well whereas in the sensorimotor cortex we found a strong contralateral bias. In addition, we found that electrodes in the subthalamic region generalize across arms better than the sensorimotor cortex and appear to be more sensitive to context (i.e., whether the other arm is engaged in the task or not). 2. Non-invasive brain stimulation (NIBS) can safely manipulate neural excitability in the human brain, providing neuroscientists with a powerful tool to advance our understanding of brain function and clinicians with novel interventions in the treatment of neurological and psychiatric disorders. We have developed a new NIBS system, kilohertz transcranial magnetic perturbation (kTMP), which can produce subthreshold modulations of neural activity with a cortical E-field of up to 7.6 V/m at 5 kHz. In two experiments we show that kTMP can modulate cortical excitability both with non-modulated waveforms at kilohertz frequencies and with amplitude modulated frequencies which are physiologically relevant for endogenous frequencies.