Wiley et al., 2004). A second major species difference was the lower baseline response rate in mice than in rats, which occurred regardless of whether the response for mice was a lever press (Vann et al., 2009; Wiley et al., 2011) or a nose poke. Because training dose affects substitution in drug discrimination and because drug-induced suppression of response rates may interfere with choice behavior, these factors may serve as alternative explanations for differences that may otherwise appear to be due to species.
