Abstract
Previous near-infrared spectroscopy (NIRS) studies using a verbal fluency task (VFT) have consistently reported that adults with attention-deficit hyperactivity disorder (ADHD) showed significantly smaller oxygenated-hemoglobin [oxy-Hb] activations in the prefrontal cortex (PFC) compared to those in healthy controls (HC). Despite this consistent evidence of brain dysfunction in ADHD, ADHD is currently diagnosed based only on subjective clinical and scoring measures, which are often unreliable. Hence, it is necessary to establish objective neuroimaging biomarkers for ADHD. While most NIRS studies have utilized averaged [oxy-Hb] values during the whole task period for group comparisons, we used a cluster-based non-parametric randomization test to compare the [oxy-Hb] time-course changes with a 0.1-s time resolution between drug-naïve adults with ADHD and HC, which may provide us with more details regarding abnormal prefrontal activation patterns in ADHD. A total of 101 participants, consisting of 63 drug-naïve adult individuals with ADHD and 38 HC, were included in this study. We identified that adults with ADHD showed significantly smaller [oxy-Hb] activations than those in HC at spatially and temporally connected clusters located in the bilateral PFC (more prominent on the left) and temporal brain region (more prominent on the left). We further found that aberrant [oxy-Hb] activation differs according to the time period during the task or according to brain location. Our findings indicate more detailed aberrant prefrontal and temporal activation patterns of ADHD compared with those in previous studies, possibly representing a biological marker for ADHD.
Highlights
Attention-deficit hyperactivity disorder (ADHD) has been classically recognized as a childhood disorder, previous longitudinal studies have found that in over half of all children with attention-deficit hyperactivity disorder (ADHD), symptoms persist into adulthood, especially with respect to inattention and impulsivity [1, 2]
There were no significant differences in age, sex ratio, and verbal fluency task (VFT) performance between the healthy controls (HC) and ADHD groups (Table 1)
As was suggested by a visual inspection of the overall near-infrared spectroscopy (NIRS) images, the [oxy-Hb] values activated by the VFT were significantly smaller in the adult participants with ADHD than in the HC at seven clusters located in the bilateral prefrontal and temporal brain regions (Table 2; Figure 1)
Summary
Attention-deficit hyperactivity disorder (ADHD) has been classically recognized as a childhood disorder, previous longitudinal studies have found that in over half of all children with ADHD, symptoms persist into adulthood, especially with respect to inattention and impulsivity [1, 2]. Deficits in neural circuits connecting brain regions of the prefrontal cortex and the striatum have been associated with this condition [5,6,7]. Despite this consistent evidence of brain network dysfunction in ADHD, ADHD is currently diagnosed based only on subjective clinical and scoring measures, which are often unreliable. While it is necessary to establish objective neuroimaging biomarkers for ADHD, previous data for adults with ADHD have been limited
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