Unconditioned stimulus (US) factors were investigated in a Pavlovian sexual conditioning paradigm with male Japanese quail (Coturnix coturnix japonica). Copulation with a female quail was more effective than exposure to a female without copulation, but the latter also produced conditioned responding (Experiment 1). The greater effectiveness of copulatory opportunity as a US was probably not due to nonassociative effects of copulation (Experiment 2). Visual cues of the female, as presented on a taxidermic model, were not effective unless the subjects had prior sexual experience that increased their response to the model (Experiments 3a and 3b). Successful conditioning with noncopulatory female exposure is significant because it allows for sexual learning to occur in a broader range of circumstances than does conditioning with copulation and because it permits conducting multiple trials per day because males do not become satiated as rapidly.

In birds as in other vertebrates, estrogens produced in the brain by aromatization of testosterone have widespread effects on behavior. Research conducted with male Japanese quail demonstrates that effects of brain estrogens on all aspects of sexual behavior, including appetitive and consummatory components as well as learned aspects, can be divided in two main classes based on their time-course. First, estrogens via binding to estrogen receptors regulate the transcription of a variety of genes involved primarily in neurotransmission. These neurochemical effects ultimately result in the activation of male copulatory behavior after a latency of a few days. Correlatively, testosterone and its aromatized metabolites increase the transcription of the aromatase mRNA resulting in an increased concentration and activity of the enzyme that actually precedes behavioral activation. Second, recent studies with quail demonstrate that brain aromatase activity (AA) can also be modulated within minutes by phosphorylation processes regulated by changes in intracellular calcium concentration such as those associated with glutamatergic neurotransmission. The rapid up or down-regulations of brain estrogen concentration presumably resulting from these changes in AA affect, by non-genomic mechanisms with relatively short latencies (frequency increases or decreases respectively within 10–15 min), the expression of male sexual behavior in quail and also in rodents. Brain estrogens thus affect behavior on different time-scales by genomic and non-genomic mechanisms similar to those of a hormone or a neurotransmitter.

Sexual reinforcers are not part of a regulatory system involved in the maintenance of critical metabolic processes, they differ for males and females, they differ as a function of species and mating system, and they show ontogenetic and seasonal changes related to endocrine conditions. Exposure to a member of the opposite sex without copulation can be sufficient for sexual reinforcement. However, copulatory access is a stronger reinforcer, and copulatory opportunity can serve to enhance the reinforcing efficacy of stimulus features of a sexual partner. Conversely, under certain conditions, noncopulatory exposure serves to decrease reinforcer efficacy. Many common learning phenomena such as acquisition, extinction, discrimination learning, second-order conditioning, and latent inhibition have been demonstrated in sexual conditioning. These observations extend the generality of findings obtained with more conventional reinforcers, but the mechanisms of these effects and their gender and species specificity remain to be explored.

Contents of learning that result from conditioned-unconditioned stimulus pairings in sexual approach conditioning were explored with male Japanese quail (Coturnix coturnix japonica). Sexual motivation of subjects conditioned to approach an arbitrary stimulus in a Pavlovian sexual conditioning paradigm was reduced by exposing them to a short photoperiod. Decreased sexual motivation resulted in a decline in sexually conditioned approach behavior (Experiments 1 and 2). Responding was restored when subjects were returned to a long photoperiod (Experiment 1) and when exogenous testosterone was administered (Experiment 2). Decreased sexual motivation did not affect food-conditioned approach behavior (Experiment 3). These results suggest that sexually conditioned approach behavior is mediated by a representation of the unconditioned stimulus, which is activated by the conditioned stimulus.

Three experiments were conducted to control for the effects of housing conditions during play deprivation on subsequent play rebound in periadolescent rats. To address play deprivation without the confound of social isolation, in Experiment 1, pairs of subjects were housed either in cages divided by wire mesh that allowed for olfactory, visual, auditory, and tactile interactions with a same-sex age-mate but prevented rough and tumble play or in standard cages. Running wheels were provided to similarly housed subjects in Experiment 2 to control for the ability to engage in physical activity. In Experiment 3, standard and brooder cages were used to control for the effects of housing area. Play-deprived subjects in all conditions showed a greatly increased number of play responses immediately following deprivation. The results from these experiments more clearly indicate that the absence of play is the crucial feature that brings about play rebound following deprivation.