Within-individual blood oxygen level-dependent (BOLD) signal variability can quantify nuanced information about brain-behavior relationships beyond that provided from average brain activation patterns. Most research examining within-individual BOLD signal variability during tasks of executive functioning has been conducted with healthy individuals across the lifespan, with limited research in clinical groups. Survivors of pediatric brain tumor have documented deficits in building-block executive functioning domains such as attention and working memory, due to various disease and treatment-related factors. This study investigates within-individual BOLD signal variability patterns in peak coordinates of an attention and working memory network during different loads of a letter n-back task in this unique clinical sample. Due to greater executive demands required in this population (e.g., compensatory strategies), greater variability was expected in common contrasts across task load types in regions of an attention and working memory bilateral frontoparietal network.

Twenty-two survivors of pediatric brain tumor (M_age(SD) = 22.91(4.40), 13 females, 15 cerebellar/posterior fossa tumors) completed a letter n-back task in an MRI scanner. After standard processing in AFNI, images were corrected for motion and physiological artifacts to reduce variability calculation confounds. Functional volumes associated with each load of the letter n-back task (0-back, 1-back, 2-back, 3-back, crosshair) were identified. Task runs were normalized (4D mean of 1 across the brain and time series), and respective run means were subtracted prior to concatenating all runs for each load type. Variability (standard deviation) was calculated across this mean-run corrected time series. Ten peak regions of interest (ROIs) were identified from “attention” and “working memory” networks, each generated from 1,000+ peer-reviewed publications gathered on NeuroSynth, for a total of 20 ROIs. Paired samples t-tests with Benjamini-Hochberg correction for multiple comparisons explored differences in variability patterns for each ROI between n-back task loads.

During task loads representative of attention, within-individual BOLD signal variability in one ROI in the 1-back versus crosshair contrast was significantly greater (left middle frontal gyrus, p = .04, d = .76). No regions demonstrated a significant difference in variability in the 0-back load versus crosshair contrast. In task loads representative of working memory, variability was significantly greater for 2-back versus 0-back loads with medium to large effect sizes in two ROIs (left superior parietal cortex, p = .02, d = .83; right inferior parietal cortex, p = .05, d = .73). Variability was also significantly greater for 3-back versus 0-back loads with a large effect size in one ROI (left superior parietal cortex, p = .02, d = .83).

This study contributes to literature examining task-based within-individual BOLD signal variability in a combined attention and working memory network in pediatric brain tumor survivors. Study results contrast with the stated hypothesis; however, research suggests that lack of significant differences in variability may illustrate neural stability. In this clinical population, greater executive effort may manifest as greater stability rather than variability. Future research can extend findings on within-individual variability during this in-scanner task to out-of-scanner measures of attention and working memory in this neurodevelopmental population.