Developmental differences in sustained and transient activity underlying working memory

Abstract

The amount of information one can maintain in working memory (WM) increases between childhood and adulthood (Gathercole, 1994, 1999; Klingberg, 1998; Luciana, 1998; Luciana and Nelson, 1998). In addition to cognitive changes that occur early in life, childhood and adolescence are periods marked by significant neuroanatomical changes that are thought to underlie cognitive maturation. This study used a mixed state-item design and a parametric "n-back" task to explore the relationship between WM load and neural activity changes with age. Thirty-five participants from two age groups (9 to 13 and 18 to 23years) were recruited. Our behavioral results indicated that children performed significantly worse than adults at loads of 2-back, but not 0- and 1-back. Our imaging results indicated that during performance of the 2-back task, children showed evidence for increased transient, but decreased sustained activity, in comparison to adults. These results suggest that for the 2-back condition, children had more difficulty maintaining task relevant information across trials and seemed to engage in a more reactive strategy wherein they reactivated context information on a trial-by-trial basis rather than maintaining over a delay. These results have important implications for understanding the development of specific processes within the WM system.

Figure 1

(a) Behavioral accuracy for the different working memory trial types. (b) Behavioral reaction times for the different working memory trial types (collapsed across 0-, 1-, and 2-back trials).

Figure 2

Regions demonstrating a significant load by age interaction for sustained activity.

Figure 3

Regions demonstrating a significant load by age interaction for transient activity.

Figure 4

(a) FMRI design comprised of 2 task blocks with 42 trials (21 task + 21 fixation) with interleaved fixation blocks of 10, 17, and 22 fixation frames (b) Examples of 0-back, 1-back, and 2-back tasks. Red letters represent targets in each of the specified conditions.