Reference: Wang, E., Sun, L., Sun, M., Huang, J., Tao, Y., Zhao, X., … & Song, Y. (2016). Attentional selection and suppression in children with attention-deficit/hyperactivity disorder. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, 1(4), 372-380.
Attention deficit/hyperactivity disorder (ADHD) is usually diagnosed through behavioural observations, such as difficulty focusing, impulsivity, and hyperactivity. Doctors and psychologists rely on interviews, checklists, and reports from teachers and parents to understand how these behaviours interfere with daily life. For example, a child with ADHD tasked with cleaning their room know they need to focus on putting their clothes away first. However, the toys sprawled out on the floor keeps distracting the child causing them to inadvertently abandon their initial task and play with the toys instead, illustrating how those with ADHD have trouble filtering out competing sights, sounds, or thoughts.
But what if we could dig deeper? Instead of only watching how someone acts, could we measure what the brain is actually doing? Research by Wang and colleagues (2016) suggests we might be able to. Using a technique called electroencephalography (EEG), scientists can record the brain’s electrical activity in real time. By looking at specific patterns of brain activity, called event-related potentials (ERPs), they can see how the brain responds to different stimuli.
This study suggests that children with ADHD may show differences in two parts of attention: selecting what matters and suppressing what distracts. This raises an exciting question: could these brain signals help us better understand ADHD and, one day, support clinical assessment?
How Brain Waves Reveal Attention in Real Time
Attention is not just about focusing harder. It also involves filtering out information that competes for your attention. EEG works by picking up tiny electrical signals from the brain through sensors placed on the scalp. On their own, these signals are messy and hard to interpret. But researchers have developed a clever trick: they look at brain responses that happen right when a specific event occurs, such as a loud sound, a visually distinct object, or even a physical sensation (i.e., a small, induced shock). These time-locked responses are called ERPs, and you can think of them as the brain’s reaction signals.
Two ERP components are especially useful for studying attention:
- The N2pc, a negative-going component reflecting attentional selection and
- The PD, a positive-going component reflecting attentional suppression.
Simply put, the N2pc helps researchers measure how strongly the brain selects something important, while the PD helps researchers measure how strongly the brain suppresses something distracting.
Most ERP research has been done with neurotypical people. But if ADHD involves differences in how the brain focuses on and ignores information, these signals might look different in children with ADHD, which could be important for diagnosis.
Testing Attention in Children With and Without ADHD
Researchers Wang and colleagues (2016) recruited 170 children (95 with ADHD, 75 without) and used EEG to record their brain activity while they completed an attention task.
In the task, children searched a screen for a target shape hidden among other shapes, responding as quickly and accurately as they could. In one version, an eye-catching but irrelevant distractor was added to the task to test whether the children could ignore it (see Figure 1). The logic was simple: stronger target selection should show up as a larger N2pc, whereas stronger distractor suppression should show up as a larger PD.
The researchers also measured each child’s ADHD symptom severity; distinguishing between inattentiveness and hyperactivity/impulsivity, as they don’t always cooccur in ADHD.
Figure 1. The tasks used in the study. The target is the gray circle, and the irrelevant distractor is the green diamond. Across the board, it is expected that the target elicits an N2pc and the distractor elicits a PD.
Children With ADHD Showed Weaker Signals for Focus and Filtering
The results showed clear differences between children with ADHD and those without, not just in how well they performed, but in what their brains were doing during the tasks.
Focusing on targets (N2pc): Both groups showed the N2pc signal when a target appeared, but in children with ADHD, the signal was noticeably weaker (See Figure 2). Their brains were less effective overall at directing attention to the target.
Figure 2. Averaged N2pc difference waves plotted from electrode positions PO7/8. Time on x-axis, amplitude on y-axis. The N2pc was significantly smaller in amplitude in children with ADHD (blue dashed) compared to typically developing (TD) children (red dashed), indicating weaker attentional selection.
Filtering out distractions (PD): When an eye-catching but irrelevant distractor appeared, children without ADHD showed a larger PD signal, suggesting their brains were actively filtering out the irrelevant information. In contrast, children with ADHD showed a much smaller PD signal, possibly because their brains have more trouble ignoring irrelevant distractors (see Figure 3). Interestingly, the researchers found that the PD signal was completely absent in some children with ADHD, suggesting that, for some children with ADHD, their brains did not show the typical neural signature of distractor suppression.
Figure 3. Averaged PD difference waves. The PD was significantly larger in amplitude in typically developing (TD) children (red dashed) compared to children with ADHD (blue dashed). This suggests that children with ADHD had a more difficult time ignoring irrelevant but distracting information.
ADHD does not look the same in every child, which is why the link between these brain signals and inattentive symptoms is especially important. Crucially, weaker N2pc and PD signals both predicted higher scores on the inattentiveness subscale, but not the hyperactivity/impulsivity subscale. This makes sense: these brain signals are associated with attentional control, not restlessness. This suggests that signals are picking up something specific to attentional difficulties, rather than ADHD symptoms in general.
Why Brain-Based Attention Measures Matter
The study suggests that ADHD isn’t just about behaviour, it may also involve real, measurable differences in how the brain processes information in real time.
This finding is huge. Right now, ADHD diagnosis relies heavily on clinical interviews, standardized rating scales, and behavioural observations, which can vary across settings and reporters. Objective brain-based markers like the N2pc and PD could eventually offer an additional window into the attention system, complementing interviews, rating scales, and behavioral observations.
ERP differences have already been found across a range of conditions, including schizophrenia, traumatic brain injury, and sleep disorders, suggesting that ERPs could one day become part of a clinician’s toolkit for understanding cognitive differences.
That said, EEG is not yet a standard clinical tool for diagnosing ADHD. More work is needed to understand how these signals vary across age, gender, development, medication status, and ADHD presentations before being used reliably in a clinical setting.
For now, this study unlocks a new possibility: attention may leave measurable signatures in the brain that can be studied alongside behaviour.
Featured Image: Free Stock Image by NomeVisualizzato from PixaBay
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