Robotic TMS mapping of motor cortex in the developing brain

The human motor cortex can be mapped safely and painlessly with transcranial magnetic stimulation (TMS) to explore neurophysiology in health and disease. Human error likely contributes to heterogeneity of such TMS measures. Here, we aimed to use recently pioneered robotic TMS technology to develop an efficient, reproducible protocol to characterize cortical motor maps in a pediatric population.

Magnetic resonance imaging was performed on 12 typically developing children and brain reconstructions were paired with the robotic TMS system. The system automatically aligned the TMS coil to target sites in 3 dimensions with near-perfect coil orientation and real-time head motion correction. Motor maps of 4 forelimb muscles were derived bilaterally by delivering single-pulse TMS at predefined, uniformly spaced trajectories across a 10 × 10 grid (7 mm spacing) customized to the participant's MRI.

Procedures were well tolerated with no adverse events. Two male, eight-year-old participants had high resting motor thresholds that precluded mapping. The mean hotspot coordinate and centre of gravity coordinate were determined in each hemisphere for four forelimb muscles bilaterally. Average mapping time was 14.25 min per hemisphere.

Traditional manual TMS methods of motor mapping are time intensive, technically challenging, prone to human error, and arduous for use in pediatrics. This novel TMS robot approach facilitates improved efficiency, tolerability, and precision in derived, high-fidelity motor maps.

Robotic TMS opens new avenues to explore motor map neurophysiology and its influence on developmental plasticity and therapeutic neuromodulation. Our findings provide evidence that TMS robotic motor mapping is feasible in young participants.