Experientia 38 (1982), Birkh/iuser Verlag, CH-4010 Basel/Switzerland 1405 Regulation of physiological functions during sleep in mammals by P. L. Parmeggiani Institute of Human Physiology, University of Bologna, Piazza di Porta San Donato 2, 1-40127 Bologna (Italy) One of the last articles by W. R. Hess is entitled 'Sleep as a Phenomenon of the Integral Organism '8. It seems worth quoting from this article the following passage, which characterizes well the attitude toward ex- perimental research of a successful pioneer in many fields of physiology. 'Once individual experiments have been concluded, it is essential that the data are interrelated and woven into a theoretical fabric. In this process of general theoretical integration I have repeatedly gained new insight particularly in respect to the organization of the diencephalon. Coordination of the findings is also necessary, if the true significance of the data is to be ascertained; this is especially true in biology.., scepti- cism toward a synthetizing approach to biology means neither more nor less than giving up hope ever to understand the integration of life functions - the alpha and omega of the unity of the individual organism.' Hess's words apply particularly to studies on the somatic and vegetative (autonomic) phenomenology of sleep. In fact, behavioral events are the result of a functional organization that can often be directly envisaged by the observer. Moreover, sleep phenome- nology is instrumental in the process of decoding into operational propositions the related patterns of elec- trical and chemical activity of neural structures. There is no doubt that an effort to achieve a theoretical integration of such propositions ought to be carried out under the guidance of the unifying concept of regulation. Following this line of thinking, this article in honor of W.R. Hess approaches from a theoretical point of view the problem of physiological regulations during sleep in mammals. L Changes in regulation during sleep The study of the homeostatic regulation 4 of physiolog- ical functions is a basic line of research whose devel- opment has revealed, however, that also non-homeo- static operations do occur. In particular, voluntary and instinctive activities during wakefulness (W) may impose a load on or interfere with homeostatic control mechanisms at central and/or effector levels, so as to overwhelm their regulatory power. Deviations of fun- damental biological variables from control ranges are, nevertheless, limited, since homeostatic mechanisms during W are capable of re-establishing a functional equilibrium. In contrast, the study of the somatic and vegetative phenomenology of sleep has shown a basic functional dichotomy. In fact, homeostatic regulation appears to be a discontinuous process, being present during synchronized sleep (SS) and absent during desynchronized sleep (DS). The experimental evidence for a dichotomy in the functional organization of SS and DS stages concerns, in particular, temperature 6,15,17, cardiovascularl3 and breathing 16'21,26 regulations. Available findings sug- gest that such a dichotomy depends basically on a change in the functional relationships between diencephalic (mainly hypothalamic) and rhombence- phalic structures. In other words, during DS, brain stem reflex and control mechanisms are released from hypothalamic regulatory influences which are active during W and SS 14' 16-18 Therefore, during DS, many biological variables are less precisely regulated and free to drift out of the normal range of homeostatic regulation. This does not always happen because of the short duration of DS episodes. At any rate, DS can be considered as a poikilostatic condition. From the regulatory point of view, the central fact is that external and internal stimuli calling for specific regulations during W and SS are less effective or even ineffective during DS. Yet, the loss of specificity of stimuli during DS is not associated to a loss of their non-specific arousing influences. The arousing effect, however, requires much higher stimulus intensities as compared to those which normally elicit the specific regulatory response. Moreover, such stereotyped behavioral responses to different stimuli clearly represent a regression in terms of the phylogenesis of regulatory mechanisms. The suspension of homeostatic regulation during DS is more evident in those functions which, like thermo- regulation, depend on control mechanisms located prevalently in the hypothalamus. In functions charac- terized by widely distributed control mechanisms, like respiration and circulation, this functional condition may be partially masked by the persistence of periph- eral autoregulation or single reflex regulation. Never- theless, also striking changes in reflex activity do occur during DS 13'21'26. Such changes are different in the different functions, depending on the degree of their normal subordination to higher levels of integra- tion. In other words, the functional condition of DS reveals phylogenetically determined levels of func- tional autonomy, as a result of the temporary regres- sion from the normal degree of diencephalization. Thus, differences in DS phenomenology among spe- cies are accounted for by inborn patterns of morpho- functional organization and autonomy of brain stem and spinal operative levels.
