Central inputs mask multiple adult neural networks within a single embryonic network

It is usually assumed that, after construction of basic network architectur e in embryos(1), immature networks undergo progressive maturation to acquir e their adult properties(2-4), We examine this assumption in the context of the lobster stomatogastric nervous system. In the lobster, the neuronal po pulation(5) that will form this system is at first organized into a single embryonic network that generates a single rhythmic pattern(6). The system t hen splits into different functional adult networks(6) controlled by centra l descending systems(7,8); these adult networks produce multiple motor prog rammes, distinctively different from the single output of the embryonic net work. We show here that the single embryonic network can produce multiple a dult-like programmes. This occurs after the embryonic network is silenced b y removal of central inputs, then pharmacologically stimulated to restore r hythmicity, Furthermore, restoration of the flow of descending information reversed the adult-like pattern to an embryonic pattern. This indicates tha t the embryonic network possesses the ability to express adult-like network characteristics, but descending information prevents it from doing so. Fun ctional adult networks may therefore not necessarily be derived from progre ssive ontogenetic changes in networks themselves, but may result from matur ation of descending systems that unmask preexisting adult networks in an em bryonic system.