A minimally invasive floating-wire interface for transcranial deep brain stimulation

Noninvasive neuromodulation technologies have advanced considerably. Yet, precise and focal activation of deep brain regions remains challenging due to the rapid attenuation of electric fields through the scalp, skull and brain tissue.

We present FLOATES (FLOAting Transcranial Electrical Stimulation), a novel approach that employs an untethered wire implanted in the brain which passively relays currents injected transcranially from the brain surface to deep brain regions, achieving focused stimulation deep within the brain.

We validated FLOATES through a combination of simulations, benchtop testing, and in vivo rodent studies. The benchtop experiments confirmed the ability to relay the field across the floating wire. Rodent studies demonstrated capability to stimulate deep brain regions in vivo.

Our simulation and benchtop testing results indicate that FLOATES can deliver significantly higher electric fields to subcortical regions compared to conventional transcranial stimulation approaches. Further in vivo results demonstrate stimulation of the deep subthalamic nucleus to evoke motor responses in limbs and demonstrate a significantly lower motor threshold compared to transcranial stimulation. Finite element simulations reveal that the efficiency of FLOATES depends on several key parameters including input field strength, wire length and diameter, exposed electrode area, electrode impedance, and tip geometry. Simulations using a human-sized head model suggest that strong enough electric fields for deep brain stimulation can be achieved with safe current levels injected through the scalp.

Together, these results establish a theoretical and experimental foundation for FLOATES as a minimally invasive and spatially precise brain stimulation platform for modulating deep neural circuits implicated in neuropsychiatric and movement disorders.