Figure 2.

Task and striatal value signals at different delays as modelled by Tanaka et al (2007) in three groups of participants who underwent tryptophan depletion, tryptophan loading, and a neutral tryptophan-balanced condition. (a) Task sequence for decision-making task, in which participants seek to remove occluding black squares to obtain rewards at different delays. In this example, choosing the white square would deliver a small amount of juice (0.8 ml) in two steps. Choosing the yellow square delivers a larger amount in four steps. The position of the squares (left or right) was changed randomly at each step. (b) Voxels within the striatum in the three-dimensional mesh surface showing a significant correlation (P<0.001 uncorrected for multiple comparisons, n=12 subjects) with V(t) modelled at different delay running from short to long coded (red:orange:yellow:green:cyan:blue). Red- to yellow-coded voxels, correlated with reward prediction at shorter time scales, are seen located in the ventral part of the striatum, whereas the green- to blue-coded voxels, correlated with reward prediction at longer time scales, are located in the dorsal part of the striatum (dorsal putamen and caudate body).