Dopamine Modulates the Efficiency of Sensory Evidence Accumulation During Perceptual Decision Making

Abstract

Background: Perceptual decision making is the process through which available sensory information is gathered and processed to guide our choices. However, the neuropsychopharmacological basis of this important cognitive function is largely elusive. Yet, theoretical considerations suggest that the dopaminergic system may play an important role.

Methods: In a double-blind, randomized, placebo-controlled study design, we examined the effect of methylphenidate in 2 dosages (0.25 mg/kg and 0.5 mg/kg body weight) in separate groups of healthy young adults. We used a moving dots task in which the coherency of the direction of moving dots stimuli was manipulated in 3 levels (5%, 15%, and 35%). Drift diffusion modelling was applied to behavioral data to capture subprocesses of perceptual decision making.

Results: The findings show that only the drift rate (v), reflecting the efficiency of sensory evidence accumulation, but not the decision criterion threshold (a) or the duration of nondecisional processes (Ter), is affected by methylphenidate vs placebo administration. Compared with placebo, administering 0.25 mg/kg methylphenidate increased v, but only in the 35% coherence condition. Administering 0.5 mg/kg methylphenidate did not induce modulations.

Conclusions: The data suggest that dopamine selectively modulates the efficacy of evidence accumulation during perceptual decision making. This modulation depends on 2 factors: (1) the degree to which the dopaminergic system is modulated using methylphenidate (i.e., methylphenidate dosage) and (2) the signal-to-noise ratio of the visual information. Dopamine affects sensory evidence accumulation only when dopamine concentration is not shifted beyond an optimal level and the incoming information is less noisy.

Figure 1.

Illustration of the experimental setup and the moving dot stimuli. The fixation cross was presented for 500 ms, the moving dots for 1000 ms. In the “cloud” of moving dots, the extent of motion coherence was varied in 3 steps by manipulating the percentages (i.e., 5%, 15%, or 35%) of dots moving in the same direction, that is, either towards left or right. The rest of the dots move randomly.

Figure 2.

The interaction MPH dosage x motion coherence x drug/placebo is shown for the drift rate parameter (v) of the DDM. The top panel shows results of MPH dosage level at 0.25 mg/kg, whereas the bottom panel shows results at the dosage level of 0.5 mg/kg group are shown. Dosage was manipulated between groups (the mean and SEM are given).