A Novel Prototype for Minimally-Invasive Transnasal Deep Brain Stimulation

Introduction: The brain’s reward circuitry is implicated in several neuropsychiatric conditions including depression, suicidal ideation, PTSD, and substance use disorder. Deep-brain stimulation of structures implicated in the reward circuitry has been increasingly studied as a potential treatment, , but this surgery involves cranial incisions and brain penetration, and carries the potential risk of intracranial hemorrhage. We developed a new technique utilizing a novel prototype inserted via a minimally-invasive transnasal approach, enabling electrical stimulation through the skull-base bones to reach targets in the deep brain.

Methods: A standalone, implantable stimulation device was created with flexible disc electrodes attached to a circuit, implemented on a flexible printed circuit-board, capable of generating voltage pulses of up to 40 V. After endoscopic insertion within the sphenoid sinus in human cadavers, we measured the electric fields generated through the skull-base into the deep brain by the device. For field recording, stereo-electroencephalography (SEEG) electrodes were inserted into the brain to create an electrode grid throughout the basal forebrain and deep frontal structures. Electrode positioning was confirmed by post-experiment computer tomography. Stimulation was performed using the novel battery-operated sphenoid implant, inserted transnasally into the bilateral sphenoid sinus with electrodes contacting the planum sphenoidale, after a minimally-invasive minor expansion of the sphenoid ostium through a sphenoidotomy. Additional testing was performed using an external power source as opposed to a self-contained battery system.

Results: Fields of > 15 V/m were measured in the basal forebrain, orbitofrontal cortex, and other diencephalic structures, demonstrating sufficient amplitude to activate neurons. Both battery-operated and external power stimulation demonstrated similar peak field shapes, with >15 V/m electrical fields in deep regions above the sphenoid sinus.

Conclusion : To our knowledge, this is the first demonstration of an implant for successful, minimally-invasive stimulation of deep brain structures through the skull base. The experiment demonstrates feasibility of transnasal electrode-placement, and that transnasal electrical stimulation can elicit electric fields with physiologically useful amplitudes in the deep brain, potentially opening up new avenues of research or device development for neuropsychiatric conditions.