How Does Inhibitory Control Differ in Adults with ADHD?

What you need to know

• Adults with ADHD show reduced brain activity related to inhibitory control compared to adults without ADHD
• The reduction in brain activity is linked to higher levels of impulsivity in adults with ADHD
• Stimulant medication may help normalize this brain activity in adults with ADHD

Inhibitory Control in ADHD

Attention-deficit/hyperactivity disorder (ADHD) is a condition that affects both children and adults. It is characterized by symptoms of inattention, hyperactivity, and impulsivity. One of the key challenges for people with ADHD is difficulty with inhibitory control - the ability to stop or withhold a response when needed.

This study aimed to better understand the brain activity underlying inhibitory control difficulties in adults with ADHD. The researchers used a technique called electroencephalography (EEG) to measure electrical activity in the brain while participants completed a task requiring inhibitory control.

The Go/NoGo Task

The researchers used a task called a Go/NoGo task to measure inhibitory control. In this task, participants see a series of images on a computer screen. For most of the images (the “Go” trials), they are supposed to press a button. However, for some infrequent images (the “NoGo” trials), they are supposed to withhold pressing the button.

This task requires inhibitory control because participants have to stop themselves from pressing the button on the NoGo trials, even though they’ve gotten into the habit of pressing it for most trials. It’s similar to how someone with ADHD might need to stop themselves from blurting out a comment or acting on an impulse.

Measuring Brain Activity

While participants completed the Go/NoGo task, the researchers measured their brain activity using EEG. EEG records electrical activity from the brain using sensors placed on the scalp. It provides very precise timing information about when different brain processes occur.

The researchers were particularly interested in a pattern of brain activity called the P3 component. The P3 occurs about 300-600 milliseconds after seeing a stimulus and is thought to reflect processes related to evaluating and categorizing information.

NoGo Anteriorization

One key measure the researchers looked at was called NoGo anteriorization (NGA). NGA reflects how much the brain activity shifts towards the front of the brain during NoGo trials compared to Go trials.

Previous research has found that during successful inhibition, there tends to be more activity in frontal regions of the brain. So a higher NGA score suggests stronger activation of frontal brain regions involved in inhibitory control.

Key Findings

The main findings of the study were:

1. Adults with ADHD showed significantly lower NGA compared to adults without ADHD. This suggests reduced activation of frontal brain regions during inhibition in ADHD.

2. Within the ADHD group, lower NGA was associated with higher scores on measures of impulsivity. This links the reduction in frontal brain activity to the behavioral symptoms of ADHD.

3. ADHD participants taking stimulant medication showed NGA levels closer to the non-ADHD group compared to unmedicated ADHD participants. This suggests medication may help normalize this pattern of brain activity.

4. The combination of fast reaction times, high error rates, and high impulsivity scores was associated with the lowest NGA in ADHD participants. This connects the brain activity differences to both symptoms and task performance.

Implications

These findings provide insight into the brain basis of inhibitory control difficulties in adults with ADHD. The reduced frontal brain activation (lower NGA) may reflect problems engaging brain regions important for stopping or withholding responses.

The link between NGA and impulsivity scores suggests this measure reflects a key aspect of ADHD symptoms. The fact that medication appeared to somewhat normalize NGA levels is encouraging and aligns with the known benefits of stimulant medications for reducing ADHD symptoms.

Limitations and Future Directions

Some limitations of this study include the relatively small sample size and the fact that about half of the ADHD participants were taking medication. Future studies with larger samples could help clarify how factors like ADHD subtype or specific medications impact these brain activity patterns.

The authors suggest NGA could potentially be used as a biological marker or “biomarker” for ADHD in the future, given the large differences seen between groups. They also note it may be a useful target for new treatments aimed at improving inhibitory control, such as neurofeedback or brain stimulation techniques.

Conclusions

• Adults with ADHD show reduced frontal brain activation during a task requiring inhibitory control
• This reduction in activation is linked to higher impulsivity symptoms
• Stimulant medication may help normalize brain activation patterns in adults with ADHD
• Measuring brain activity during inhibition tasks may provide a useful way to better understand ADHD and develop new treatments in the future

While more research is needed, this study provides important insights into the brain basis of inhibitory control challenges in adult ADHD. Understanding these underlying brain differences can help inform treatment approaches and reduce stigma by showing the biological basis of ADHD symptoms.