
Positive feedback systems 161
If the feedback can be blocked in such a system, and if the feedba ck-blocked
system is known (or correctly intuited bas ed on biological insight) to be mono-
tone, then if the experimentally determined steady- state stimulus-response
curve of the feedback-blocked system is sigmoidal, the full feedback system is
guaranteed to be bistable fo r some ra nge of feedback strengths. Conversely, if
the open-loop system exhibits a linear resp onse, a Michaelian response, or any
response that lacks an inflection point, the feedback system is guaranteed to
be monostable des pite its feedback. Thus, some degree of “cooperativity”