I have a theory.

I believe mercury can act like an excitotoxin when it enters a nerve cell, causing them to fire without proper signaling.

Mercury, in its elemental state, cannot pass through cells walls, but when combined with certain things, can easily pass through cell walls.

One of the things that enables mercury to pass through cell walls is caffeine. For this reason, I am not surprised to find that many people control their tinnitus (ringing in the ears) by stopping all intake of caffeine. IMPORTANT: If you take in even a small amount of caffeine, it will allow the tinnitus to continue. You must stop ALL caffeine and, in most cases I've been familiar with, the tinnitus has stopped or decreased 80% to 90%.

Hope this helps someone.