fNIRS-Based Clinical Assessment of ADHD Children fNIRS-Based Clinical Assessment of ADHD Children

While a growing body of neurocognitive research has explored the neural substrates associated with attention deficit hyperactive disorder (ADHD), an objective biomarker for diagnosis has not been established. The advent of functional near-infrared spectros- copy (fNIRS), which is a noninvasive and unrestrictive method of functional neuroimag ing, raised the possibility of introducing functional neuroimaging diagnosis for young ADHD children. In search of a stable and clinically applicable biological marker, here in this chapter, we first discuss a plausible solution to enable the objective monitoring of the acute effects of ADHD medications at the group level. Subsequently, we discuss our suc cessful visualization of differential neural substrates between ADHD and healthy control children for inhibitory control at the individual level, which reached an optimized clas sification parameter with a value of 85% and a sensitivity of 90%. These findings led us to postulate that fNIRS-based examination would allow the identification of an objective neuro-functional biomarker to diagnose and determine the appropriate treatment for ADHD children. We believe that such a novel technical application would evoke wide interest from neuroimaging researchers. a go/no-go task. All ADHD patients were pre-medicated with MPH (n = 16) or ATX (n = 16) as part of their regu lar medication regimen. We performed fNIRS measurements of ADHD subjects twice (the times of day for both measurements were scheduled to be as close as possible), at least 2 days apart, but within 30 days. Control subjects underwent a single, non-medicated session. On each examination procedure day, ADHD subjects underwent two sessions, one before drug (MPH/ATX or placebo) administration, and the other 1.5 h after drug administration. Before each pre-administration session, a washout period of 2–3 days was undertaken by all ADHD subjects. Each session involved 6 each of go (baseline) and go/no-go (target) blocks, which were alternated. Each block lasted 24 s and was preceded by trial instructions displayed on a PC monitor for 3 s, giving an overall block-set time of 54 s and a total session time of about 5.5–6.0 min. In the go blocks, we presented subjects with random sequences of two animal pictures and asked them to press a button for both pictures as quickly as possible. In the go/ no-go blocks, we presented subjects with a no-go picture 50% of the time, thus requiring subjects to respond to half the trials (go trials) and inhibit their response to the other half (no-go trials). After ADHD subjects performed the first session, either MPH/ATX or a placebo was administered orally. We generated stimuli and collected responses using E-Prime 2.0 associated with go/no-go task performance. The administration of MPH and ATX led to a degree of right prefrontal activation in ADHD children comparable to that of the healthy con trol subjects, but the placebo did not. These results suggest that as observed using fNIRS, nor malized right IFG/MFG activation associated with inhibition control would serve as a robust neurobiological marker for evaluating both MPH and ATX effects. In summary, we explored the feasibility of introducing fNIRS-based neuropharmacological assessment of the effects of MPH/ATX administration to ADHD children, and concluded that the IFG and MFG activation could serve as robust objective neurobiological markers to visualize the effects of MPH/ATX on ADHD children based on the following observations. Furthermore, with group analyses, we suc cessfully visualized differential neural substrates for ADHD and healthy control children for inhibitory control. The inhibition task recruited the right IFG/MFG, and activation was sig nificantly high during the go/no-go task (Cohen’s d : 1.009). Those results led us to postulate that right IFG/MFG activations for a go/no-go task, as observed using fNIRS, might be used as an objective neuro-functional biomarker to differentiate school-aged ADHD children and healthy controls at the individual level. Consequently, our next challenge was to explore the inhibition-related dysfunction in ADHD children at an individual level. We explored a method for individual classification between ADHD and healthy control sub jects using fNIRS, emphasizing how spatial distribution and amplitude of the hemodynamic response associated with go/no-go task execution can be utilized. To do this, we needed to identify the cut-off amplitude of cortical activation of each ROI mentioned above in order to differentiate ADHD children from healthy control children. We focused on individual oxy-Hb signal change during target (go/no-go) sessions at multichannel locations for the right MFG and IFG, where a go/no-go-task-related activation in control subjects was conspicuously large