whereas home-cage procedures do not allow for easy assessment of this behavior. The fact that motor activity and food intake are rarely measured in operant experiments indicates that specificity of drug effects cannot always be determined, although the presence of an alternate reinforcer can give a crude indication of response perseveration, indiscriminate responding or the absence of responding. Due to possible limited resources (e.g., time, equipment, etc.) operant studies on pharmacological treatments have often been acute, rather than chronic, in nature. Acute rather than chronic treatment is a drawback of many pharmacological studies in general (e.g., Leeman et al., 2010). Finally, as noted in the next section, very few studies have been conducted in multiple rat lines which limit interpretation of the findings, especially as they relate to generalizability across multiple populations.
