The Funkenstein test has been analyzed by Gellhorn,1 who showed how to use it to test the excitability of the hypothalamus. According to Gellhorn's neurophysiological analysis of the Funkenstein methacholine (Mecholyl) test, the methacholine-induced fall of blood pressure is signaled to the hypothalamus; the hypothalamus reflexly signals for a sympathetic discharge, and the sympathetic discharge raises the blood pressure back to its basal level. The amount of sympathetic discharge depends upon the strength of the reflex signal from the hypothalamus, and the strength of the reflex signal depends upon the degree of hypothalamic excitability. The measurement of blood pressure changes following methacholine, therefore, amounts to a measure of hypothalamic excitability.
A visual analog of the Funkenstein test was examined by validating the visual test against the blood pressure test of hypothalamic excitability. The visual test was developed from the finding of the Soviet psychologist,