BT - a sound designer friend, Brian Tibbetts, thinks this could explain synesthesia:

"but imagine some freaky experiments/research where they manipulated this protein and subsequent ion flooding with non sonic related methodology..

like through drug therapy. like squirting a fluid into the ear, vibrational/magnetic/EM manipulation, or even, like, a scent, a piece of food, a drink or something..

*This would cause people to hear things when there was no actual source of physical sound. And what would they hear? Could it be tweaked? How far?? ;)

Perhaps research in this vein will help explain the bizarre phenomenon of synesthesia where people’s neurological sensory processing systems are strangely wired.. causing them to, for instance, see sounds, hear colors, etc. Wild!"