Within-session changes in licking as a function of sucrose concentration in common marmosets

Common marmosets (Callithrix jacchus) were allowed to lick sucrose solutions freely in 30-min sessions. We examined how the rate of licking changed in the course of a session and how the pattern of changes was affected by different concentrations (1%, 5%, and 25%) of solutions. The results showed that licking rates decreased monotonically regardless of the concentrations and that the decreasing patterns could be reasonably explained by exponential functions. The rates of decrease were slowest for the 5% solution and fastest for the 1% solution. The linear relation between the number of licks in a short interval and the cumulative number of licks before that interval, which was suggested by Aoyama (1996), did not always hold. The cumulative records of licking for individual sessions revealed that a break-and-run pattern of licking sometimes dominated after a licking rate slowed down, and that this pattern could disturb the linear relation.