Neural basis of protracted developmental changes in visuo-spatial working memory

Abstract

Developmental studies have shown that visuo-spatial working memory (VSWM) performance improves throughout childhood and adolescence into young adulthood. The neural basis of this protracted development is poorly understood. In this study, we used functional MRI (fMRI) to examine VSWM function in children, adolescents, and young adults, ages 7-22. Subjects performed a 2-back VSWM experiment that required dynamic storage and manipulation of spatial information. Accuracy and response latency on the VSWM task improved gradually, extending into young adulthood. Age-related increases in brain activation were observed in focal regions of the left and right dorsolateral prefrontal cortex, left ventrolateral prefrontal cortex (including Broca's area), left premotor cortex, and left and right posterior parietal cortex. Multiple regression analysis was used to examine the relative contributions of age, accuracy, and response latency on activation. Our analysis showed that age was the most significant predictor of activation in these brain regions. These findings provide strong evidence for a process of protracted functional maturation of bilateral fronto-parietal neural networks involved in VSWM development. At least two neural systems involved in VSWM mature together: (i) a right hemisphere visuo-spatial attentional system, and (ii) a left hemisphere phonological storage and rehearsal system. These observations suggest that visually and verbally mediated mnemonic processes, and their neural representations, develop concurrently during childhood and adolescence and into young adulthood.

Figure 1

Increase in accuracy and decrease in RT during the WM and control tasks as a function of age. Slopes and intercepts from a regression analysis for each variable are shown above each graph.

Figure 2

Surface rendering (A) and coronal views (B) of brain areas that showed significant increases in activation with age during the WM, compared with the control, task. Significant activation was observed in the left and right DLPFC, left VLPFC, left PMC, and left and right PPC.

Figure 3

Age-related increase in activation in the left and right PFC and PPC during the WM task. Cluster size (A) and peak t score (B) results are shown for two separate quantitative measures of activation in each cluster.