| Summary: | 博士 === 國立臺灣大學 === 臨床醫學研究所 === 104 === Introduction
Individuals with Attention deficit/hyperactivity disorder (ADHD) has core symptoms of inattention and hyperactivity/impulsivity, and show a broad range of deficits in neuropsychological domains. Although neuroimaging studies have highlighted the brain structural abnormality in ADHD, its association with neuropsychological performance has rarely been studied. Hence, this thesis is concerned with these questions. We used diffusion spectrum imaging (DSI) to reconstruct white matter tracts and to measure the microstructural property of selected fiber tracts, and adopted voxel-based morphometry (VBM) approach to identify the variation of regional gray matter (GM) or white matter (WM) volume. We aimed to investigate the different neural substrates underpinning neuropsychological performance in children with ADHD, in terms of attentional performance, executive functions and intra-individual variability (IIV) in reaction time.
Method
We try to answer our study question with three studies with specific aims: (1) To find altered white matter tract property in children with ADHD, and to examine how them are associated with impaired attentional performance; (2) To explore whether there are different white matter tracts involving in executive functions in youths with ADHD; (3) To investigate how regional volumes would be related to IIV based on the ex-Gaussian parameters in ADHD. The first two studies used DSI method. We focused on several white matter tracts which may related with attentional performance and executive functions, which included frontostriatal (FS) tract (including striatum to dorsolateral prefrontal cortex, ventrolateral prefrontal cortex and orbitofrontal cortex), superior longitudinal fasciculus (SLF), arcuate fasciculus (AF) and cingulum bundle (CB). We compared the generalized fractional anisotropy (GFA) values of the white matter tracts between the ADHD and individually-matched controls. We also used backward elimination procedure to identify the fitted model containing the variables from these tracts which maintained significant effects on measures of neuropsychological tasks. The third study used VBM method to conduct an whole-brain analysis about the correlations between IIV and regional brain volume in ADHD and individually-matched controls.
Results
【Study 1】
In 50 youths with ADHD and 50 matched controls, youths with ADHD had lower GFA in left frontostriatal tracts, bilateral SLF and right CB. Our study highlights that alteration of the right SLF in GFA values was most significantly associated with the clinical symptom of inattention in ADHD youths. Besides FS tracts, the GFA value of the SLF, CB were also associated with attention performance in youths with ADHD and controls.
【Study 2】
In 45 youths with ADHD and 45 matched controls, youths with ADHD had lower GFA in the left FS tract, left SLF, left AF and right CB. The ADHD and control groups demonstrated different association patterns between executive functions and fiber tract microstructural property. Most of the executive functions were associated with microstructural property of the FS tract and CB in controls, while with that of the FS tract, SLF and AF in youths with ADHD.
【Study 3】
Using 55 ADHD youths and individually-matched controls, we identified several neural substrates underpinning IIV in ADHD youths. For GM, IIV was associated with regional volume in right superior temporal gyrus, right posterior insula and bilateral cerebellum in ADHD youths. There was significant IIV-by-group interaction in cingulate cortex, thalamus and right inferior frontal gyrus. For WM, IIV was associated with regional volume in the left uncinate fasciculus, the bilateral inferior cerebellar peduncle and the left superior corona radiata. There was significant IIV-by-group interaction in the genu of corpus callosum, right anterior corona radiata, left splenium of corpus callosum, and the arbor vitae of bilateral cerebellum.
Discussion
The involvement of different fiber tracts or alternation of regional brain volume in neuropsychological performance in ADHD may imply neuropathological underpinnings of ADHD or the possibility of a compensatory mechanism.
Conclusions
Our studies highlight that structural neural substrates underpinning the neuropsychological functions are atypical in youths with ADHD.
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