Abstract
In the early 1960s intrinsically generated widespread neuronal discharges were discovered to be the basis for the earliest motor behavior throughout the animal kingdom. The pattern generating system is in fact programmed into the developing nervous system, in a regionally specific manner, already at the early neural plate stage. Such rhythmically modulated phasic bursts were next discovered to be a general feature of developing neural networks and, largely on the basis of experimental interventions in cultured neural tissues, to contribute significantly to their morpho-physiological maturation. In particular, the level of spontaneous synchronized bursting is homeostatically regulated, and has the effect of constraining the development of excessive network excitability. After birth or hatching, this “slow-wave” activity pattern becomes sporadically suppressed in favor of sensory oriented “waking” behaviors better adapted to dealing with environmental contingencies. It nevertheless reappears periodically as “sleep” at several species-specific points in the diurnal/nocturnal cycle. Although this “default” behavior pattern evolves with development, its essential features are preserved throughout the life cycle, and are based upon a few simple mechanisms which can be both experimentally demonstrated and simulated by computer modeling. In contrast, a late onto- and phylogenetic aspect of sleep, viz., the intermittent “paradoxical” activation of the forebrain so as to mimic waking activity, is much less well understood as regards its contribution to brain development. Some recent findings dealing with this question by means of cholinergically induced “aroused” firing patterns in developing neocortical cell cultures, followed by quantitative electrophysiological assays of immediate and longterm sequelae, will be discussed in connection with their putative implications for sleep ontogeny.
Highlights
Even after more than a half-century of concerted research efforts, a number of stubborn semantic conundrums are still associated with the concept of “sleep”
An especially long-standing blind spot has been the general reluctance to appreciate the singular contributions made along the way by in vitro cell culture experiments in establishing a sound theoretical basis for understanding the essential features of sleep phenomenology
Subsequent investigations revealed that “type IV” motility comprises a broad class of behaviors—
Summary
Even after more than a half-century of concerted research efforts, a number of stubborn semantic conundrums are still associated with the concept of “sleep”. Despite an impressive degree of normal morpho-physiological maturation even in the total absence of bioelectric activity [29], a number of central effects have since been revealed using quantitative methods, perhaps the most important of which being a homeostatic up-regulation of net excitatory drive within spinal cord cultures following prolonged suppression of spontaneous spike discharges [30,31,32].
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