Pharmacological evidence for the implication of noradrenaline in effort
Fig 5
Clonidine affects choice and force production.
Behavior of the monkeys under the placebo (gray) and clonidine (brown) conditions. Lines and dots represent group-level means (across monkeys) and error-bars represent SEM (across sessions). A. Relationship between the percentage of high-required force choices and the difference in offered forces. The weight of the difference in required force increased under clonidine (clonidine = −2.55 ± 0.23, placebo = −1.65 ± 0.28, F(1,145) = 14.81, p = 1.78×10−4). B. Relationship between the percentage of high-reward choices and the difference in offered rewards. Under clonidine, the weight of the difference in reward sizes did not change (clonidine = 2.29 ± 0.21, placebo = 2.45 ± 0.30, F(1,145) = 0.47, p = 0.49). C-D. Relationship between exerted force relation and chosen force level (C) and chosen reward size (D). The dotted line represents the optimal relation (identity) between exerted force and force difficulty (the minimum required force to complete the trial). Clonidine had a main effect on force production (clonidine = 0.55 ± 0.05, placebo = 0.63 ± 0.03, F(1,145) = 20.70, p = 1.12×10−5), without affecting the effects task factors (reward weights: clonidine = 0.02 ± 8.3×10−3, placebo = 0.02 ± 5×10−3, F(1,145) = 0.93, p = 0.33; required force weight: clonidine = 0.06 ± 0.01, placebo = 0.05 ± 0.01, F(1,145) = 0.92, p = 0.33). E-F. Relationship between participation and the sum of offered forces (E) and sum of offered rewards (F). There was a tendency for an increase in the weight of the sum of required forces that did not reach significance (clonidine = −0.75 ± 0.18, placebo = −0.46 ± 0.04, F(1,145) = 2.02, p = 0.16) (E) but no effect of clonidine on the modulation of participation by the sum of rewards (F). Underlying data can be found in S1 Data. au.,arbitrary units; Fmax, maximal force; HF, high force; HR, high reward.