Verbal fluency tasks and attention problems in children with ADHD: evidence from fNIRS

Abstract

Background: Functional near-infrared spectroscopy (fNIRS) is a promising non-invasive neuroimaging tool for assessing cortical activity in children with attention-deficit hyperactivity disorder (ADHD). While Verbal Fluency Tasks (VFTs) are widely used in adolescents and adults, their application in younger children remains underexplored. This study aimed to examine cortical activation during a VFT in children with ADHD and its association with attention-related behavioral symptoms.

Methods: Thirteen children with ADHD (aged 7-9) and 13 matched neurotypically developed controls completed a VFT while undergoing fNIRS. Activation in the dorsolateral prefrontal cortex (DLPFC) was analyzed using mean amplitude, center of gravity (COG), and initial slope. Associations with the Swanson, Nolan, and Pelham Rating Scale (SNAP-IV) and Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V) scores were examined.

Results: Children with ADHD showed significantly lower DLPFC activation and widespread negative patterns compared to neurotypically developed peers (p < 0.05). Mean activation amplitude was significantly correlated with inattention scores on both the SNAP-IV and DSM-V scales.

Discussion: fNIRS revealed altered DLPFC activation in children with ADHD during VFT, underscoring its potential as an objective tool to support clinical assessment of attention deficits in younger populations.

Keywords: ADHD; VFT; attention; children; fNIRS.

Figure 1

fNIRS tasks. (A) Verbal fluency test task. (B) Scanning setup.

Figure 2

(A) fNIRS probe design: sources are represented by red dots labeled with “S” and a number, while detectors are represented by blue dots labeled with “D” and a number. The optodes are arranged with a 30-mm spacing between them. (B) Channels are indicated by red dots labeled “CH” followed by a number.

Figure 3

(A) Level of brain activation in children with ADHD performing a verbal fluency task, with color bars indicating t-statistics, colors that are approximately cooler indicating lower t-values, and warmer colors indicating higher t-values. (B) Level of brain activation in neurotypically developed children performing a verbal fluency task, color bars represent t-statistics, colors that are approximately cooler indicate a lower t-value, and colors that are warmer indicate a higher t-value.

Figure 4

(A) HbO time-series curve over the full task sequence. This line plot shows mean HbO concentrations over time in the ADHD group (red) and neurotypically developed group (blue) across a 125-s trial window, including the pre-task baseline (first 30 s), the 60-s active VFT period, and the post-task baseline (final 35 s). Neurotypically developed children displayed a clear task-induced increase in HbO during the activation phase, followed by a gradual return to baseline. In contrast, children with ADHD showed a flat or declining HbO pattern during the task phase. (B) Mean HbO amplitude during task period. This bar chart compares the mean HbO signal intensity in the DLPFC during the 60-s VFT activation window between the ADHD and Neurotypically Developed groups. The neurotypically developed group showed significantly higher mean HbO levels compared to the ADHD group (p < 0.05). (C) Center of gravity (COG) of the HbO signal. This measure captures the temporal distribution of the hemodynamic response, reflecting when the “center” of the activation occurs during the trial period. Both ADHD and neurotypically developed groups showed similar COG values, with peak response occurring in the early-to-mid phases of the VFT period (p > 0.05). (D) Initial slope of HbO response after task onset. This metric represents the rate of increase (or decrease) in HbO concentration within the first 5 s of the VFT task period. Both groups demonstrated a rapid rise in HbO, and no significant difference was observed in the slope between ADHD and neurotypically developed children (p > 0.05).

Figure 5

(A) Mean values of oxyhemoglobin during a verbal fluency task in children with ADHD and neurotypically developed children correlated significantly (p < 0.05) with scores on the DSM-V (Inattention). (B) Mean values of oxyhemoglobin during a verbal fluency task in children with ADHD correlated significantly (p < 0.05) with scores on the SNAP-IV (Inattention).