Functional near-infrared spectroscopy in developmental psychiatry: a review of attention deficit hyperactivity disorder

Abstract

Research has linked executive function (EF) deficits to many of the behavioral symptoms of attention deficit hyperactivity disorder (ADHD). Evidence of the involvement of EF impairment in ADHD is corroborated by accumulating neuroimaging studies, specifically functional magnetic resonance imaging (fMRI) studies. However, in recent years, functional near-infrared spectroscopy (fNIRS) has become increasingly popular in ADHD research due to its portability, high ecological validity, resistance to motion artifacts, and cost-effectiveness. While numerous studies throughout the past decade have used fNIRS to examine alterations in neural correlates of EF in ADHD, a qualitative review of the reliability of these findings compared with those reported using gold-standard fMRI measurements does not yet exist. The current review aims to fill this gap in the literature by comparing the results generated from a qualitative review of fNIRS studies (children and adolescents ages 6-16 years old) to a meta-analysis of comparable fMRI studies and examining the extent to which the results of these studies align in the context of EF impairment in ADHD. The qualitative analysis of fNIRS studies of ADHD shows a consistent hypoactivity in the right prefrontal cortex in multiple EF tasks. The meta-analysis of fMRI data corroborates altered activity in this region and surrounding areas during EF tasks in ADHD compared with typically developing controls. These findings indicate that fNIRS is a promising functional brain imaging technology for examining alterations in cortical activity in ADHD. We also address the disadvantages of fNIRS, including limited spatial resolution compared with fMRI.

Keywords: ADHD; Children; Executive functions; Neural correlates; fNIRS.

Figure 1

PRISMA 2020 flow diagram for new systematic reviews which included searches of databases and registers only Selection of studies to include in the review. *Studies were excluded based on the following criteria: a) utilized fNIRS for functional brain imaging, (b) subjects included children with ADHD (age < 18 years) and typically developing controls, (c) reported the location of fNIRS optodes based on the international 10/20 system to facilitate comparison across studies, and (d) utilized executive function tasks (response inhibition, attention, cognitive flexibility, working memory, etc.) to elicit brain activation. Figure flowchart adapted from Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi: 10.1136/bmj.n71 and http://www.prisma-statement.org/

Figure 2.. Overlap between fNIRS and fMRI studies across EF tasks.

The spheres represent regions affected in ADHD during EF performance. The spheres are color-coded to differentiate regions reported only in fNIRS studies (turquoise), only in fMRI studies (pink), or those common across fNIRS and fMRI studies (yellow). The radius of the sphere corresponds to the number of fNIRS studies that reported activity in a region. This does not apply to fMRI-only studies. This figure was created using BrainNet Viewer (http://www.nitrc.org/projects/bnv/) (Xia et al., 2013).