Neural Development of Rule Use and Flexibility

What brain regions support the development of rule use in childhood? Crone et al. attempt to answer this question in this new article from the Journal of Neuroscience.

The article begins with a quick review of the literature suggesting dissociable developmental trajectories for simple rule use, and the ability to switch between those rules. For example, previous behavioral research by the lead author showed that children's active maintenance of rules does not show adult activation patterns until adolescence, whereas neural activity related to rule switching showed adult-like activation at 12 years of age.

The authors predicted that in a task involving two levels of rule difficulty, ventrolateral prefrontal cortex (VLPFC) would show increased activity for bivalent relative to univalent rules. In contrast, the pre-supplementary motor area (pSMA) was predicted to show activity during rule switches. These hypothesis were tested on 62 subjects from three age groups - 8-12 year-olds, 13-17 year-olds, and 18-25 year-olds - by administering the following task. Subjects had to respond with a left-arrow key press to a picture of a tree, but a right-arrow key press to a picture of a house, if they had just previously been cued with a picture of a triangle. If they had been cued with a picture of a circle, these mappings were reversed. Finally, if cued with a bidirectional arrow, the following pictures would be either a flower or a car, requiring left and right key presses respectively. IQ scores were also measured for each participant with Raven's matrices. An ROI analysis including parietal cortex, pSMA, and vlPFC was conducted on the fMRI data.

Despite the varying ages of the groups, all participants were given the same amount of training on the task prior to scanning. In retrospect, it would have been better to train participants to a certain performance criterion, since you cannot be sure that age differences do not merely represent differences in "practice efficacy" unless you equate participants for performance before the task begins.

The results from a blocked version of the task showed that subjects were less accurate for the bivalent rules than for univalent rules, and that the two youngest groups did not differ from each other in terms of their relative accuracy on bivalent and univalent rules (not surprisingly, the difference in accuracy between bivalent and univalent rules was lower for the oldest age group). Similarly, reaction times were much slower on bivalent trial types in general, and the two lowest age-groups did not significantly differ in their RTs on such trials.

In mixed blocks, results were somewhat different. Although the 13-17 year-olds did not significantly differ in their accuracy switch costs for bivalent trials from either the younger or the older age-group, the authors interpret this result to show that "switching ability" reaches adult levels of performance at the beginning of adolescence. Bizarrely, age differences in switching were only reflected in terms of accuracy - RTs did nto significantly differ between the groups. Equally bizarrely, there were no differences between rule-repeat and rule-switch trials.

The fMRI data showed increased bilateral pSMA activity for bivalent relative to univalent rules, but there were no age differences in this reulst; also, this comparison did not turn up activation differences in parietal or vlPFC ROIs.

The authors interpret these results to suggest that children experience more difficulty on bivalent rules relative to univalent rules than do older age groups, as reflected by widely-spread increases in neural activity. Such increases were prominent among the older age groups only in mixed blocks. Unfortunately, it is difficult to take more away from this study than "people of different ages use their brains differently," which is not surprising, given that brains differ between people of different ages!


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