Increased RTV in ADHD: A Novel Approach to Detect Inattention [Florida International University]

Abstract

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder and the second most common mental condition in U.S. children, affecting more than 6.1 million individuals between the ages of 2-17 years. Defined by two behavioral features - inattention and hyperactivity - identifying and studying ADHD, especially related periods of inattention, a defining feature, poses an important limitation. Recent studies have identified elevated reaction time variability (RTV) as a reliable feature of ADHD, that may be related to periods of inattention. However, the neural mechanisms behind RTV, and thereby inattention, are not well understood. The default mode network (DMN) is a functional brain system responsible for internally-directed mental processes, that is active when not engaged in cognitively demanding externally directed tasks. Activation of the DMN during active states, thus, could disrupt externally directed behavior and related neurobiological mechanisms – perhaps acting as an internal distraction. We predicted that activation in the DMN during an externally directed task will be elevated during periods of increased RTV. Further, we anticipated DMN activation to precede abnormally slow responses. We used blood-oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) while participants with and without ADHD performed a standard sustained attention to response (SART) task. We then examined the activation of the DMN during episodes of aberrant RTV, defined as reaction times more than two standard deviations from the preceding measure of variability, to ascertain the nature of the aforementioned association. The neurobiological mechanisms that are related to the attention-deficit in ADHD must be better understood to aid in diagnosis and treatment. This study aims to be the first to provide comprehensive evidence of the neural underpinnings behind increased RTV and thereby inattention in individuals with ADHD. The current system to diagnose ADHD in children is based on potentially subjective behavioral observations by parents and teachers. Identifying increased RTV as a behavioral marker of ADHD with a well-characterized neurobiological mechanism may enable a more effective and objective method of diagnosis, resulting in more successful treatment outcomes and decreased costs of care for families of children with the disorder.