Have you heard of PMS?
That’s an interesting case, first of all because it is periodic, that is, if a woman claims to have been temporarily insane because of PMS, then he blood hormone and neurotransmitter levels can be measured the following month. Eventually, this may become the legal standard, for this little used excuse.
To be adjudged temporarily insane, by a clinical standard, hormones and neurochemicals have to be severely off the norm, so much so that little subjectivity would be involved.
In the case of PMS, it is known to specifically affect the brain chemical serotonin.
http://en.wikipedia.org/wiki/Serotonin
Most serotonin is used in the gut, but that part in the CNS has various functions, including the regulation of mood, appetite, sleep, muscle contraction, and some cognitive functions including memory and learning.
If your serotonin levels are way off, you know it.
However, this is very different from “The Twinkie Defense”, in which *subjectively* courts have determined temporary insanity, which I agree is nonsense, except perhaps under such severe emotional stress that anyone would be expected to lose their sense, such as seeing a family member at extreme risk.