The neural regulation of circulation explored in the frequency domain.

The neural regulation of circulation has mainly been explored on the basis of the phasic reflex changes that it undergoes when a disturbance is imposed upon the system. This approach brought to the artificial fragmentation of the whole regulatory network into a legion of presumed simple reflexes and to the subsequent attempt to reconstitute a unitary vision from a collage of fragments. Although we have surely enriched our knowledge along this path, the danger of overlooking some obvious shortcomings became also quite clear. For instance, when reconsidering the words of Sherrington [29] "a simple reflex is probably a purely abstract conception, because all parts of the nervous system are connected together ... and it is a system certainly never absolutely at rest", we cannot help realizing that this caution has surprisingly disappeared from a field, the neural control of circulation, which has to be envisaged as a "closed-loop system" [27]. Instead, to make an example, we usually interpret the baroreflexes as if they were simple reflexes initiated only by a restricted although bilateral reflexogenic area, while it has been demonstrated not only that multiple reflexes of the same sign [27] but also