Early Pavlovian studies on the effects of starvation. A contribution to the history of neurodietetics

This communication is based on the pioneering studies performed by I. P. Pavlov's associates, Yu. P. Frolov (in 1918) and I. S. Rozental' (in 1918/1919) at the Institute of Experimental Medicine, in Petrograd. The changes in the "independent variable"--the dogs' diet--were not planned but were the consequences of severe shortages of food for man and beast. The principal generalization concerns the order in which different forms of "complex nervous activity" were impaired: the order is opposite to the order in which they emerge in the process of ontogenesis. First to suffer was "internal inhibition," as documented by the failure of stimulus differentiation. This was followed by the decrease in the magnitude of well-established conditional responses (CRs). As a result of a more severe impairment of the excitatory processes, it became difficult or impossible to establish new CRs. In time, previously established CRs to artificial stimuli, visual and acoustic, disappeared totally. The CRs to natural conditional stimuli (CSs) were maintained fairly well but, eventually, they too decreased markedly. In the terminal phase of starvation, the unconditional salivary reflexes continued to function, although their magnitude was depressed.