Fig. 3. Relationship between extent of depletion and instrumental reversal learning performance.

a Reward-punishment (R-P) condition. b Reward-neutral (R-N) condition. Both correlations were significant. ΔTRP:LNAA is the change in the ratio of tryptophan to large neutral amino acids; 0 indicates no change. A greater decrease (post-depletion minus pre-depletion blood plasma results) in the TRP:LNAA ratio indicates a more extensive depletion (more negative y-axis values). Reversal learning is indexed here as the number of trials to criterion in the second reversal block. Increasing x-axis values represent more trials to criterion and thus worse reversal performance. Shading indicates ±1 standard error (SE).