Age-differences in odor preference following an odor-illness pairing

Abstract

An ambient maple odor was paired with illness in rats ranging in age from weaning to old age. The animals then were tested for an aversion to a maple-odored solution. The results indicated no aversion to the odored solution at any age level and, hence, support previous research indicating that odor is a weak cue for illness. However, both young-adult and old-age rats made ill after drinking water in the absence of odor preferred the maple-odored solution to plain water. This finding suggests that, whereas odor may be a weak cue for illness in adult rats, it may be an effective safety signal. In contrast, weanling rats made ill in the presence of the odor preferred the odored solution. This paradoxical preference was explained in terms of olfactory imprinting and the effect punishment has on imprinted responses.When rats are exposed to a novel odor , even for a brief period of time , their subsequent preference for that odor increases. There appears to be little variation in this effect in rats ranging from infancy to adulthood (Caza & Spear , 1984). However, if the novel odor is paired with an illness-inducing agent , then there are striking differences in odor preferences for rats of different age groups . When illness follows odor in adult rats , there is very little change in preference for the odor. Odor appears to be a weak signal for illness for these animals (Garcia & Koelling , 1967;Hankins, Garcia, & Rusiniak , 1973). In infant rats , on the other hand, odor is such an effective cue for illness that even second-order odor aversions are easily established (Cheatle & Rudy, 1978. Unlike adults, infant rats are highly dependent upon olfaction for a variety of behaviors (e.g., sucking , homing, etc.), and, hence , differences in the effectiveness of odor as a signal for illness may reflect the fact that olfactory cues are more salient for infant rats than for adults. The salience of olfactory cues should decrease for the rat as its reliance on olfactory input diminishes with the development of other sensory systems . Because a variety of the rat's sensory systems (e.g., visual , auditory, etc.) become functional well before the postweaning period (Alberts, 1984), it would seem that there should be little or no difference in the effectiveness of odor as a cue for illness in rats from weaning to old age , assuming of course that the olfactory system remains functional. Recently , however, Misanin, Peterson , Valliere, Blatt, and Hinderliter (1985) reported differences in the effect odor has on conditioned taste averPlease address correspondence to: J. R. Misanin, Psychology Department, Susquehanna University, Selinsgrove, PA 17870. sion in weanling, young-adult , and old-age rats . Odor had a strong potentiating effect on the aversion to taste in young adults , had a weaker potentiating effect in weanlings, and had no effect in old-age rats. It is possible, then, that the effects of age in processing odor cues persist well into the postweanling period. Thus, the purpose of the present experiment was to determ...