Analysis of Sniffing of the Albino Rat 1)

Abstract Sniffing behavior of albino rats was photographed on movie film at 30, 32, or 64 frames per sec. The ontogenetic development of sniffing was studied and the component movements were described. The effects of olfactory, somatic, visual, and auditory stimuli, and of certain drugs, nerve sections, and cerebral ablations upon sniffing were examined. The following results were obtained: "Sniffing" by rats consists of an integrated and precisely timed movement sequence in which four distinct synergistic muscle groups participate to produce: (a) bursts of polypnea, (b) recurrent protraction and retraction of mystacial vibrissae, (c) repetitive retraction and protraction of the tip of the snout, and (d) a rapid series of discrete head movements and fixations. These four component movements occur at rates between 5-11/sec. in bursts of varying duration (1-10 sec.). Some of these movements may occur independently of the others, but when they all occur together, which is more common, they blend at the same rate and in a fixed temporal pattern with respect to one another. The sniffing bursts are brought into play when the animal is aroused to explore by olfactory, visual, auditory, or tactile stimulation. Sniffing actions are not dependent on olfactory or tactile vibrissae input for their initiation or synchronous patterning despite the fact that the main adaptive values of these actions would seem to be those of olfactory and somatic sensory perception. In normal rats, olfactory input affects sniffing activities by regulating the degree of their persistence; the duration being affected by the character of the olfactory stimuli encountered. Thus, aversive stimuli are contacted only briefly, whereas, preferred stimuli elicit prolonged bursts of sniffing. Each of the four component movements of the sniffing sequence emerge at different times during ontogeny. This suggests that separate neural centers driving them also mature at different times. As each type of movement appears, it swings into synchrony with those actions already present. Interruption of olfactory input does not alter the normal rate of sniffing. Interruption of somatic sensory input from vibrissae may reduce the overall sniffing rate slightly. Bilateral ablation of neocortex drastically interferes with the sniffing sequences. In the decorticate rat these actions were elicited only with difficulty; the sharpness of the individual movements was blurred, and their magnitude and rate were diminished. The possibility that these effects are not directly related to cortical control of sniffing patterns is suggested. The various lines of evidence indicate that sniffing is a fixed and stable response pattern that is relatively independent of age and of long or short term experiential factors.