A short-term poikilothermic period occurs just after paradoxical sleep onset in humans: characterization changes in sweating effector activity.

We examined the changes in sudorific effector activity in five healthy young (21-23 y) subjects just before, during and just after successive paradoxical sleep (PS) phases. Local sweat rates were evaluated minute by minute over the chest (mcs). Previous observations, showing that mcs levels dropped before paradoxical sleep onset was electrophysiologically scored, were confirmed. At the end of this period of mcs depression, which in the present study coincided with paradoxical sleep onset, we show for the first time a short period (3-7 min) (period I) during which sweat production completely disappeared. A second period then followed (period II), at the very beginning of which mcs was re-elicited and thereafter increased in close correlation with paradoxical sleep duration. During period II, the remaining inhibiting influences (maximal during period I) and their releases could be specified by the successive valleys (indicating mcs inhibition) and peaks (indicating release of the mcs inhibition) drawn by the minute by minute mcs changes. These inhibitions became weaker as paradoxical sleep advanced. Given the strategic position of period I (at paradoxical sleep onset) and the total mcs abolition therein observed, it may be assumed that this poikilothermic state is the re-emergence of the 'ancestral' mode of body temperature regulation. From a thermophysiological point of view, period II may be considered as more 'modern' and directly related to the extension of paradoxical sleep in humans. This extension could be underlain by the unique development of our cognitive and/or learning functions.