Developmental aspects and neurobiological correlates of working and associative memory.

Objective: It has been shown that verbal working and associative memory have different developmental trajectories with working memory, taking a linear course from early childhood to adolescence, whereas associative memory takes a curvilinear course asymptoting at about age 12. This study made a determination of whether these trajectories tracked with 2 magnetic resonance spectroscopy imaging (MRSI) variables: phosphocreatine level (PCr) and gray matter percentage (GM%).

Method: In a cross-sectional study, 94 children ranging in age from 6-14 years were administered tests of verbal working and associative memory and underwent an MRSI procedure evaluating 6 major brain regions. The study considered PCr levels and GM% in the 6 regions. Loess curves were constructed plotting the memory tests and MRSI variables across age, and trajectories were evaluated.

Results: PCr showed a linear increase with age, particularly in the left superior temporal lobe with this increase closely tracking improvement in working memory but not associative memory scores. GM% did not increase with age in any brain region, and there was no tracking with either of the memory tests.

Conclusion: Verbal working memory and verbal associative memory have differing age trajectories, with working memory showing close tracking with PCr level, mainly in the left superior temporal lobe. No such tracking was found for the associative memory tests. GM% curves were flat across regions, showing no association with age.