Neural changes in control implementation of a continuous task

Abstract

It is commonly agreed that control implementation, being a resource-consuming endeavor, is not exerted continuously or in simple tasks. However, most research in the field was done using tasks that varied the need for control on a trial-by-trial basis (e.g., Stroop, flanker) in a discrete manner. In this case, the anterior cingulate cortex (ACC) was found to monitor the need for control, whereas regions in the prefrontal cortex (PFC) were found to be involved in control implementation. Whether or not the same control mechanism would be used in continuous tasks was an open question. In our study, we found that in a continuous task, the same neural substrate subserves control monitoring (ACC) but that the neural substrate of control implementation changes over time. Early in the task, regions in the PFC were involved in control implementation, whereas later the control was taken over by subcortical structures, specifically the caudate. Our results suggest that humans possess a flexible control mechanism, with a specific structure dedicated to monitoring the need for control and with multiple structures involved in control implementation.

Figure 1.

The behavioral performance of all subjects in early and late blocks during compatible and incompatible conditions. Subjects' performances improved significantly for the incompatible condition, from early to late blocks; also, in the early blocks, performance during the compatible condition was better than that during the incompatible condition. Asterisks indicate significant differences between blocks (p < 0.05). 95CI, 95% confidence interval.

Figure 2.

Top, The contrast between early incompatible and compatible conditions (I₁ > C₁) reveals prefrontal regions (areas BA9 and BA45) involved in movement control implementation. A, Anterior; P, posterior; R, right; L, left. Bottom, The graphs show the BOLD signal for each region and each condition in all blocks of the experiment. Error bars indicate SEM. The arrows point to the same activated cluster in different planes.

Figure 3.

The areas activated by the contrast between early and late incompatible blocks (I₁ > I₃) in which subjects show significant activation in the PFC and ACC. The corresponding contrast for compatible blocks (C₁ > C₃) showed no significant activation using the same statistical threshold. Error bars indicate SEM. The arrows point to the same activated cluster in different planes. A, Anterior; P, posterior; R, right; L, left.

Figure 4.

The change in BOLD signal from early to late incompatible blocks in the ACC correlated significantly (negatively) with behavioral improvements observed during the same blocks (incompatible condition; left graph) but not during compatible condition (right graph).

Figure 5.

Top, Mean tracking accuracy of high and low improvers during early and late compatible and incompatible blocks. Poor improvers did not change their performance over time or across conditions. High improvers had low performance in the incompatible compared with the compatible condition only early in the experiment, but they improved significantly late in the experiment. Bottom, The regions activated by the contrasts I₁ > C₁ (left) and I₁ > I₃ (right) in the high-improvers group. No regions were activated by the same contrasts in the low- improvers group. The arrows point to the same activated cluster in different planes. 95%CI, 95% confidence interval; A, anterior; P, posterior.

Figure 6.

A, Two regions in the caudate nucleus, bilaterally, were activated significantly by the contrast I₃ > I₁. A, Anterior; P, posterior. B, C, The activation in the left caudate correlated significantly negatively with the activation in the PFC only during the incompatible but not the compatible condition (B) and only for subjects in the high improvers group (C).