Becoming Consistent: Developmental Reductions in Intraindividual Variability in Reaction Time Are Related to White Matter Integrity

Abstract

Cognitive development is known to involve improvements in accuracy, capacity, and processing speed. Less is known about the role of performance consistency, and there has been virtually no empirical examination of the neural underpinnings of within-person variability in development. In a sample of 92 healthy children and adolescents aged 8 -19 years, we aimed to characterize age-related changes in trial-to-trial intraindividual variability (IIV) of reaction time (RT) and to test whether IIV is related to white matter (WM) integrity as indexed by diffusion tensor imaging. IIV was quantified as the SD of correct RTs in a speeded arrow flanker task, and Tract-Based Spatial Statistics was used to test relationships with diffusion characteristics. Large age-related reductions in IIV in both simple congruent trials and more complex incongruent trials were found. Independently of sex, age, and median RT (mRT), lower IIV was associated with higher fractional anisotropy and lower overall diffusivity. Effects were seen for IIV in one or both trial types in the corticospinal tract, the left superior longitudinal fasciculus, the uncinate fasciculus, the forceps minor, and in the genu and splenium of the corpus callosum. There were no significant associations between mRT and any of the diffusion indices. The findings support the proposition that developmental reductions in IIV reflect maturation of WM connectivity and highlight the importance of considering within-person variability in theories of cognitive development and its neurobiological foundation.

Individual Differences in Resting Corticospinal Excitability Are Correlated with Reaction Time and GABA Content in Motor Cortex

“…Previous studies have failed to observe a relationship between MRS measures of M1 GABA and intracortical inhibition, measured with paired-pulse TMS protocols using interpulse intervals of 2.5 or 3 ms (Stagg et al, 2011b;Tremblay et al, 2013). Whereas paired-pulse TMS protocols are hypothesized to measure intracortical inhibitory mechanisms, the goal of our study was to explore the relationship between GABA concentrations within M1 and intrinsic corticospinal excitability, not intracortical inhibition.…”

“…Spectra were zero-filled from 1024 to 4096 data points, apodized with a 4 Hz Gaussian function, and manually phase corrected and aligned to creatine (Cr; Evans et al, 2013;Near et al, 2015). A combined automated and manual routine was used to identify spectra containing large numbers of extreme values that were excluded from further analysis (Near et al, 2013). The mean percent averages removed (of 64 averages total) was 0.5 Ϯ 0.4% for the LPF, 0.4 Ϯ 0.3% for the M1, 0.3 Ϯ 0.2% for the PM, and none for the OCC voxel.…”

“…An extensive transcranial magnetic stimulation (TMS) literature has accumulated over the past 25 years describing changes in corticospinal (CS) excitability during the preparation and execution of responses (Starr et al, 1988;PascualLeone et al, 1992;Hasbroucq et al, 1999;Leocani et al, 2000;Duque and Ivry, 2009;Duque et al, 2010;Greenhouse et al, 2015a,b). Variation in task performance has also been related to contextual, or state-based changes in task-independent factors: For example, variability in the compressive force of a response during a simple reaction time (RT) task can be explained by fluctuations in resting activity within somatomotor cortex (Fox et al, 2007).…”

“…MRS measurements of GABA concentrations in primary motor cortex (M1), taken at rest, correlated positively with RT, such that individuals with higher basal levels of M1 GABA tended to have slower RTs during the performance of a sequence learning task (Stagg et al, 2011a). Counterintuitively, individuals with more excitable CS pathways, measured with TMS, exhibited higher concentrations of M1 GABA and glutamate (Stagg et al, 2011b). These results suggest that greater M1 GABA corresponds to an intrinsically more excitable CS pathway, but is also associated with slower RTs.…”

Lower white matter microstructure in the superior longitudinal fasciculus is associated with increased response time variability in adults with attention-deficit/hyperactivity disorder

“…19 The reduction of RTV during adolescence has been partially linked to the maturation of white matter tracts in the brain. 20 A recent study performed in young patients with ADHD and healthy controls showed that FA of the left cingulum bundle (CB) was negatively correlated with τ only in patients with ADHD. 13 Importantly, the CB is part of the attentional network model as defined by Makris and colleagues.…”