production of these 50 KHz USVs was assessed during a 10-min period of social interaction with an age- and sex-matched conspecific, adolescents were found to produce significantly fewer positive calls than adults during this “consummatory” period, even though the adolescents engaged in significantly more social behavior during the test than adults (Willey et al., 2009). These results are highly replicable and are not due to a competition between production of 50 KHz USVs and expression of social behavior, given that social deprivation is positively correlated with both frequency of social behavior and 50 KHz USVs (Knutson et al., 1998; Willey et al., 2007). Thus, results of these USV experiments suggest a developmental dissociation between social behavior and 50 KHz USVs emitted in that context – a presumptive index of the hedonic value of social interactions.
