Nice theory, but it has a flaw : effects on the body of the wizards do affect their mind, eating chocolate helps to counter the Dementor effect, alcohol seems to have the normal effect, and (at least in canon) the wizard teens are affected by hormones like normal teens. So it would require the magic to scan that, and affect the mind in a similar way than a normal chemical effect on the brain would work, but yet still preserve the "resistant to damage" property ? Well, starts to be quite un-occamian.