The findings they speak of are not surprising at all…
The Temporomandibular joint (TMJ) is blessed with many mechanoreceptors and receives innervation from Cranial Nerve V (trigeminal nerve) and the upper cervical spine. There is physiological overlap through the trigeminocervical nucleus (in the upper midbrain or mesencephalon, the principal sensory nucleus) which receives the same innervation from the trigeminal nerve distribution and the upper 4 cervical neuromeres(nerve levels) (so double input into same pathway). Nicoli Bogduk published abody of research on this, along with Susan Lord and Leslie Barnsley.
The upper 4 cervical nerve root levels also directly input into the flocculonodular lobe of the cerebellum (which coordinates alot of motor activity, especially of axial extensor muscles). This preloads the motor neuronal pool (just like contracting your muscle slightly, or clenching to get a better response from a reflex exam). By optimizing input (through a bite guard), you optimize mechanoreception, which optimizes cerebellar activity, which in turn pre loads the motor neuronal pool. You would get SIMILAR ( and better tasting!) results with having them clench or bite down on gum, though not as good due to possible imperfect mechanics.
We have not seen all of the research but we are sure it is legit. It’s like an orthotic for the mouth. Keep in mind changing bite mechanics closer to symmetrical occlusion will be helpful ( ie. Orthodontics, invisalign etc).