I think this is the reasoning that confuses people. Cilantro is a chelator capable of crossing the blood brain barrier. ALA can do this as well. These chelators don't have specific actions that selectively removes mercury from the brain, it ALWAYS can go both ways. From how I understand it, they can pick up mercury anywhere in the body, and drop it anywhere in the body.

If you just take one big dose, They pick up a lot of mercury, you excrete a little bit of that mercury, and it drops the rest of the mercury all over the body, including the brain. This is called redistribution. All chelators we know of have this downfall, and redistribution is dangerous and can over the long term make you much sicker by concentrating mercury in sensitive areas in the body/brain.

This is why Andy Cutler developed a protocol to keep a steady dose of chelator in the bloodstream, by taking frequent doses of a chelator rather than one large dose. So you would continually excrete mercury but you would have much less redistribution, making it a much safer option.