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Internal or motivational factors and external or signal factors were assessed to determine their role in motor-food response during conditioning in cats and dogs. Under experimental water-salt dysbalance visceral signalling was shown to be an essential factor involved in a goal-directed response. In addition to dominant motivation, a conditioned food signal seems to be this factor. In search for neurophysiological correlates of food motivation, we studied responses of n. tractus solitaris in rats to adequate chemical stimulation of the tongue receptors and viscerochemoreceptors. 3 groups of neurons were distinguished: those responding to the stimulation of only one receptive zone (taste and viscerochemical neurons) and neurons responding to the stimulation of both receptive areas ("convergence" units). Under salt deprivation, threshold concentrations of salt for responses from n. solitaris decreased and the response from a convergence neuron to viscerochemical stimulation diminished following application of sodium chloride on the tongue receptor.

In experiments on unrestrained carps, a comparative study was made of the analysis of different concentrations of NaCl and HCl (starting with threshold ones) by means of instrumental conditioned reflexes, aimed at eliminating harmful chemical stuffs from water medium. Salt concentrations, in response to which the formation of a conditioned reflex is possible (3--9 mM) are by an order higher than those for the acid (0.3--0.85 mM). The intensity and duration of manifestation of the defensive conditioned reflex depend directly on the strength (concentration) of the chemical stimulus. Cessation of motor conditioned reaction providing for restoration of the optimal conditions of the surrounding takes place when initial concentration of the stimuli in experimental reservoir is reduced to values close to threshold ones, namely to about 2 mM for NaCl and to about 0.2 mM for HCl, i.e. to a minimal concentration compatible with normal vital activity. After extirpation of the forebrain, the fish lose the capacity for active elimination from the surroundings of both salt and acid components.