Learning Cognitive Flexibility: Neural Substrates of Adapting Switch-Readiness to Time-varying Demands

Abstract

An individual's readiness to switch tasks (cognitive flexibility) varies over time, in part, as the result of reinforcement learning based on the statistical structure of the world around them. Consequently, the behavioral cost associated with task-switching is smaller in contexts where switching is frequent than where it is rare, but the underlying brain mechanisms of this adaptation in cognitive flexibility are not well understood. Here, we manipulated the likelihood of switches across blocks of trials in a classic cued task-switching paradigm while participants underwent fMRI. As anticipated, behavioral switch costs decreased as the probability of switching increased, and neural switch costs were observed in lateral and medial frontoparietal cortex. To study moment-by-moment adjustments in cognitive flexibility at the neural level, we first fitted the behavioral RT data with reinforcement learning algorithms and then used the resulting trial-wise prediction error estimate as a regressor in a model-based fMRI analysis. The results revealed that lateral frontal and parietal cortex activity scaled positively with unsigned switch prediction error and that there were no brain regions encoding signed (i.e., switch- or repeat-specific) prediction error. Taken together, this study documents that adjustments in cognitive flexibility to time-varying switch demands are mediated by frontoparietal cortex tracking the likelihood of forthcoming task switches.

Figure 1.

Experimental task. An example color-cue mapping is shown where blue cues the parity task (odd or even) and red cues the magnitude task (< 5 or > 5).

Figure 2.

Behavioral (a) response time and (b) accuracy data for the context task-switch paradigm. Error bars denote 1 between-subjects standard error of the mean.

Figure 3.

(a) Model-fit learning rates for model 1, derived from the HBI procedure. The bin width for generating the stacked plot was set to .013. (b) Mean RTs as a function of model-derived unsigned PE. RTs were sorted into quartiles according to PE. RTs flagged as outliers in the main analysis were again excluded. Error bars denote 1 between-subjects SEM.

Figure 4.

Switch-related activity across all trials.

Figure 5.

Parietal and frontal regions whose activity scaled with unsigned switch prediction error are displayed on axial brain slices.

Figure 6.

Conjunction of switch > repeat and unsigned PE whole-brain analyses.

Figure 7.

(A) Leave one subject out regions of interest. BOLD response in the (B-D) left parietal cortex, (E-G) right parietal cortex, and (H-J) left precentral/inferior frontal gyri as a function of trial type and switch PE quartile. Shaded regions and error bars denote 1 between-subjects SEM. The bar plots denote activity taken at 5 seconds post stimulus onset, reflecting the peak of the hemodynamic response.