Utility of the N-back task in survivors of childhood acute lymphoblastic leukemia.

The N-back task is often used in functional brain imaging studies to activate working memory networks; however, limited information is available on its association to clinical outcomes in children or cancer survivors. A total of 137 survivors of acute lymphoblastic leukemia (ALL; mean current age = 14.3 years, SD = 4.8; time since diagnosis = 7.6 years, SD = 1.6) completed the N-back task and comprehensive neurocognitive testing, including standardized measures of attention, processing speed, and working memory. Results indicated that females demonstrated significantly slower reaction times (0-back p = .02; 1-back p = .03) than males. Survivors <15 years old at the time of testing demonstrated a significant decrease in accuracy as working memory load increased compared to survivors ≥15 years old (p < .001). Performance on the N-back task was associated with nonverbal working memory (rs = .56, p < .001) in survivors ≥15 years of age. For younger survivors, N-back performance was more strongly associated with attention skills. Results suggest the N-back assesses different cognitive constructs at younger compared to older childhood ages. These age differences should be considered in interpreting functional brain imaging results.