Effects of Trigeminal Nerve Stimulation on the ANS and Proprioception: High Frequency TNS Reduces Proprioceptive End-point Error

Previously accomplished research examined sensory integration between upper limb proprioception and tactile sensation. The active proprioceptive-tactile relationship points towards an opportunity to examine neuromodulation effects on sensory integration with respect to proprioceptive error magnitude and direction. Efforts to improve focus and attention during upper limb proprioceptive tasks results in a decrease of proprioceptive error magnitudes and greater endpoint accuracy. Increased focus and attention can also be correlated to neurophysiological activity in the Locus Coeruleus (LC) during a variety of mental tasks. Through non-invasive trigeminal nerve stimulation, it may be possible to affect the activity of the LC and induce improvements in arousal and attention that would assist in proprioceptive estimation. The trigeminal nerve projects to the LC through the mesencephalic nucleus of the trigeminal complex, providing a pathway similar to the effects seen from vagus nerve stimulation. In this experiment, the effect of trigeminal nerve stimulation (TNS) on proprioceptive ability is evaluated by the proprioceptive estimation error magnitude and direction, while LC activation via autonomic pathways is indirectly measured using pupil diameter, pupil recovery time, and pupil velocity. TNS decreases proprioceptive error magnitude in 59% of subjects, while having no measurable impact on proprioceptive strategy. Autonomic nervous system changes were observed in 88% of subjects, with mostly parasympathetic activation and a mixed sympathetic effect.