The neuron doctrine: a revision of functional concepts.

The functional tenets of the ineuiron doctrine were reviewed some time ago(l3), but there hlas been little attempt to correct obvious deficiencies or formulate new concepts that take iinto account the great amount of anatomical and physiological work of recent years. Among these sttudies, the findings of synapses betweeni (lendrites of nerve cells are of partictular interest (reviewe(d in 4). Tlle reports are by now sufficiently numerous and well-documented to indicate that dendrodendritic synapses are a widespread and important phenomenon in the vertebrate niervous systemn, especially the mammalian brain. However, the patterfns of connections andl the functions they mediate have been difficult to comprelhend within the context of the classical doctrine. It is timely tlherefore to reappraise the neuroin doctrine in the light of recent work. Discussion will be focuissedl on1 the mammalian olfactory bulb, where dendro(lendritic synapses were first identified(5) and wlhere the case for a revision of classical concepts can be set fortlh most clearly. Specific proposals will be made, that the neutroni can no longer be regarded as the basic functional unit of the nervotus system; ratlher, the nervotus system is organized on the basis of ftunctional uinits wlhose idlentity in many cases is independent of neuronal boundaries. It will be showni that these proposals are supported by increasing evidence from otlher work that goes beyond the confines of thle classical doctrine.