Sleep as an instinct: the last experimental research of Giuseppe Moruzzi

Abstract

This short paper summarises the last experimental research period (1970-1975) of Professor Giuseppe Moruzzi on the topic of the sleep as an instinctive behaviour. The main goal was “the study of the levels of reticular activation which are required for the onset of different type of instinctive behaviours”. By the earliest research line the sleepwaking cycle in acute and chronic thalamic pigeons and the effects of the reticular formation stimulation were studied. The electrical stimulation of the pontine reticular formation produced a range of effects according to the animal’s level of wake or sleep: the spontaneous pecking towards the grain, for example, was interrupted and the pigeon shifted toward other behavioural activities, but started again to peck at the end of stimulation. Moreover, repeated trains of stimulations at higher voltage were able to induce sleep. These results suggested the existence of ascending fibres from the caudal brainstem able to block the instinctive activities which were distinct from the fibres responsible of the awakening phenomena. In the very last experiments the level of general arousal (general drive) and its relationship with the motivated behaviour (specific drive) were studied by Professor Moruzzi. The experiments were aimed to establish a setting of strong motivation for selected “specific drive” such as bow-cooing behaviour – induced by testosterone administration – and pecking behaviour – induced by apomorphine administration –, in order to test the effect of “general drive” by modulating the intensity of the background illumination, being this latter considered a natural activator of general arousal. The results obtained supported the hypothesis that any kind of “specific drive” requires a given level of general activation “general drive” for its overt manifestation which, in turn, is the result of the balance between activating and de-activating reticular structures.