Adult functional magnetic resonance imaging (fMRI) literature suggests that a left-right hemispheric dissociation may exist between verbal and spatial working memory (WM), respectively. However, investigation of this type has been obscured by incomparable verbal and spatial WM tasks and/or visual inspection at arbitrary thresholds as means to assess lateralization. Furthermore, it is unclear whether this hemispheric lateralization is present during adolescence, a time in which WM skills are improving, and whether there is a developmental association with laterality of brain functioning. This study used comparable verbal and spatial WM n-back tasks during fMRI and a bootstrap analysis approach to calculate lateralization indices (LIs) across several thresholds to examine the potential of a left-right WM hemispheric dissociation in healthy adolescents. We found significant left hemispheric lateralization for verbal WM, most notably in the frontal and parietal lobes, as well as right hemisphere lateralization for spatial WM, seen in frontal and temporal cortices. Although no significant relationships were observed between LI and age or LI and performance, significant age-related patterns of brain activity were demonstrated during both verbal and spatial WM. Specifically, increased adolescent age was associated with less activity in the default mode brain network during verbal WM. In contrast, increased adolescent age was associated with greater activity in task-positive posterior parietal cortex during spatial working memory. Our findings highlight the importance of utilizing non-biased statistical methods and comparable tasks for determining patterns of functional lateralization. Our findings also suggest that, while a left-right hemispheric dissociation of verbal and spatial WM is apparent by early adolescence, age-related changes in functional activation during WM are also present.
Bibliographical noteFunding Information:
Portions of this study were presented at the annual meeting of the Cognitive Neuroscience Society, March, 2009, San Francisco, California. This research was supported by Oregon Clinical and Translational Research Institute (UL1 RR024140), R01 AA017664 (Nagel), K08 NS52147 (Nagel), F31 AA019866 (Herting), and UNCF/MERCK Postdoctoral Science Research Fellowship (Fair), Ford Foundation Research Fellowship (Fair), and K99/R00 MH091238 (Fair). The authors express appreciation to Dr. Joan Stiles for her invaluable assistance in task conceptualization for this project.
- Working memory