Within-session response rate in rats decreases as a function of amount eaten

In past studies, within-session changes of rat feeding behavior were always treated as functions of time. This study aimed to describe the within-session decreases of operant response as a function of cumulative amount of food intake. Rats (n = 8) were trained to obtain food pellets by lever-press responses. Session lengths were 45 min. The following results were observed: 1) Response rates during a CRF schedule were well described as a linear function of cumulative amount of food pellets eaten; 2) The linear equation was also accurate in describing the response rates during a semi-VI schedule; and 3) Even if schedules of reinforcement were changed within a single session, response rates in each reinforcement schedule were well described as linear functions of cumulative food intake. Thus, response rates decreased proportionally to the increase in cumulative amount of food intake.