The glutamate that causes brain damage is always free. The glutamate in MSG is always free. When free glutamate is taken into the mouth, it triggers glutamate receptors in the mouth and on the tongue, causing them to fire.
If there’s a moderate amount of free glutamate involved, a glutamate receptor will be activated once and will transmit its chemical message to the next glutamate receptor in line until the goal receptor has been triggered.
When multiple glutamate-containing ingredients are taken into the mouth, the nerves that are triggered fire repeatedly until the glutamate receptors at which the firing glutamate neurotransmitters are aimed, become overstimulated and die. And the nerve cells that are obliterated in this way, are not replaced with neurons (nerve cells). And the functions those obliterated cells would have regulated had they not been destroyed — like controlling appetite and satiety involved in obesity and controlling reproductive function for example — will never be replaced. Think obesity epidemic and infertility crisis.