Dopamine and task switching control

Background

Genetic variability related to the catechol-O-methyltransferase (COMT) gene (Val158 Met polymorphism) has received increasing attention as a possible modulator of cognitive control functions. Dopamine (DA) plays a key role in the regulation of executive functions in the prefrontal cortex. Val/Val homozygous individuals are assumed to be associated with low tonic DA levels in PFC, whereas Met/-carriers are assumed to be associated with high tonic DA levels in PFC. Met/-carriers have high DA levels in the PFC, which may be beneficial for the cognitive stability, but which may reduce the flexibility. Val/Val homozygous have low DA levels in the PFC, which may result in the opposite.

Method

Healthy humans (n=87), genotyped for the Val158Met polymorphism at the COMT gene, performed a task-switching paradigm, which provides a relatively diagnostic index of cognitive flexibility. The amount of the time needed to switch between two different tasks can be taken to indicate the efficiency in adapting and restructuring cognitive representations, so that smaller switching costs would reflect a higher level of cognitive flexibility. The sequence of the task switch was regular and predictable. Therefore the interval before the next stimulus would function as a preparation interval. The shorter the preparation interval, the less likely the reconfiguration would have been completed before the stimulus was presented. This would fit with the observation that switching costs were more pronounced with short than with long Response Stimulus Intervals (RSIs).

Result

As predicted, Met/-carriers showed larger switching costs (i.e., less cognitive flexibility), F(1,85) = 4.28, p < 0.05, than Val/Val homozygous individuals. Our findings support the idea that low prefrontal dopamine levels promote cognitive flexibility. No significant differences were found among genotype by age, sex, or estimated IQ.