Test-retest reliability of functional connectivity in depressed adolescents

Abstract

ABSTRACTThe test-retest reliability of fMRI functional connectivity is a key factor in the identification of reproducible biomarkers for psychiatric illness. Low reliability limits the observable effect size of brain-behavior associations. Despite this important connection to clinical applications of fMRI, few studies have explored reliability in populations with psychiatric illnesses or across age groups. We investigate the test-retest reliability of functional connectivity in a longitudinal cohort of adolescents with and without major depressive disorder (MDD). Measuring reliability is complex and several metrics exist that can offer unique perspectives: for example, univariate metrics capture reliability of a single connection at a time while multivariate metrics reflect stability of the entire connectome. We compare a widely used univariate metric, intraclass correlation coefficient (ICC), and two multivariate metrics, fingerprinting and discriminability. Depressed adolescents were more reliable than healthy adolescents at the univariate level (0.34 > 0.24; Wilcoxon rank-sum:p< .001), and both groups had poor average ICCs (<0.4). Multivariate reliability was high in both groups: fingerprinting (FIHV= 0.53; FIMDD= 0.45; Poisson(1) testp< .001) and discriminability were above chance (DiscrHV= 0.75;DiscrMDD= 0.76; 500-fold permutation testp< .01). Reliability was not associated with symptoms or medication, suggesting that there is not a strong relationship between depression and reliability. These findings support the shift towards multivariate analysis for improved power and reliability.