Change in electrical potential was measured before and after application and a dose-response curve was constructed with R2 value of 99.92%.

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"The absence of a dose-response curve was disappointing, " says Jeffrey Cummings of UCLA. Moreover, he noted that the drug only very modestly reduced levels of a nasty protein called tau in the spinal fluid.

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Calabrese says that many poisons follow, instead, a U-shaped curve: The death rate goes down as the dose climbs from zero to a certain small amount, what you could call the optimal exposure.

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