Figure 2.

Rats exhibit individual differences in preference for the uncertain reward, and this determines the response to amphetamine and eticlopride. a, Wager-sensitive rats shifted their preference as the bet size increased, whereas the choice pattern of wager-insensitive rats did not change. b, The degree of wager sensitivity shown by each rat, as indicated by the gradient (m) of the line obtained by plotting choice of the uncertain lever against bet size. c, d, Amphetamine increased choice of the uncertain option in wager-sensitive (c) but not wager-insensitive rats (d). e, f, In contrast, eticlopride had no effect in wager-sensitive rats (e), but decreased uncertain choice in wager-insensitive animals (f). Data shown are mean ± SEM.