How Does Brain Structure Relate to Attention Problems in Adult ADHD?

What you need to know

• Adults with ADHD showed differences in the structure of brain white matter tracts compared to adults without ADHD
• These brain structure differences were linked to more variable attention and reaction times in adults with ADHD
• The findings help explain the biological basis for attention problems in adult ADHD

Background on ADHD and Attention Variability

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental condition that often persists into adulthood. Adults with ADHD frequently struggle with inattention, hyperactivity, and impulsivity. One key feature of ADHD is highly variable attention and performance - individuals may be very focused and quick to respond in one moment, but slow and inattentive the next.

This moment-to-moment variability in attention and reaction times, known as intra-individual variability, has been suggested as an important marker of ADHD. However, the underlying brain basis for this variability is not well understood. Some researchers have proposed that differences in the structure of white matter - the “wiring” that connects different brain regions - may help explain attention variability in ADHD.

Studying Brain Structure and Attention in Adult ADHD

To investigate this, researchers conducted a study comparing 53 adults with ADHD to 50 adults without ADHD. They used a brain imaging technique called diffusion tensor imaging (DTI) to examine the structure of white matter tracts throughout the brain. DTI measures the movement of water molecules in brain tissue, which provides information about the organization of white matter fibers.

The researchers focused on a measure called fractional anisotropy (FA), which indicates how organized and intact white matter structure is. Higher FA values generally suggest more organized white matter structure.

To measure attention variability, participants completed a simple reaction time task where they pressed a button as quickly as possible when a cross appeared on a computer screen. The researchers analyzed how much participants’ reaction times varied from trial to trial.

Key Findings on Brain Structure and Attention

The study found several key differences between adults with ADHD and the comparison group:

1. Adults with ADHD showed lower FA values in parts of the corticothalamic tract, a white matter pathway connecting the cortex (the outer layer of the brain) to the thalamus (a structure deep in the brain that relays sensory and motor signals). This suggests less organized white matter structure in this pathway in ADHD.

2. Adults with ADHD had more variable reaction times, specifically showing more extremely slow responses. This was measured by a value called tau, which represents the proportion of abnormally slow reaction times.

3. In the ADHD group, lower FA values in the corticothalamic tract were associated with higher tau values (more variable attention). This relationship was not seen in the comparison group.

Implications for Understanding ADHD

These findings provide new insight into the brain basis of attention problems in adult ADHD. The corticothalamic tract is involved in relaying information between brain regions important for attention and sensory processing. Less organized structure of this tract may lead to less reliable transmission of signals, potentially explaining why attention and reaction times are more variable in ADHD.

Importantly, the link between white matter structure and attention variability was specific to the ADHD group. This suggests that differences in brain structure may create a vulnerability to attention fluctuations in ADHD, rather than causing variability in everyone.

The researchers note that even on a very simple reaction time task with no complex decision-making required, adults with ADHD showed more variable performance. This indicates that inconsistent attention in ADHD likely stems from differences in basic cognitive and neural processes, rather than difficulties with more complex thinking.

Limitations and Future Directions

While this study provides valuable new information, there are some limitations to consider:

1. The brain imaging measure used (FA) is somewhat non-specific - lower FA could indicate several different types of changes in white matter structure. More advanced imaging techniques could provide more detailed information in future studies.

2. The simple reaction time task, while useful for isolating basic attention processes, does not capture the full range of attention difficulties people with ADHD experience in daily life. Studies using more complex, real-world tasks could build on these findings.

3. This study focused on adults, so the results may not apply to children with ADHD. Future research could examine how white matter structure and attention variability may differ across development in ADHD.

Conclusions

• Adults with ADHD show differences in the structure of the corticothalamic white matter tract compared to adults without ADHD
• These structural brain differences are linked to more variable attention and reaction times in ADHD
• The findings suggest that altered white matter organization may create a vulnerability to fluctuating attention in adult ADHD
• Understanding the brain basis of attention problems could eventually lead to better diagnosis and treatment approaches for ADHD

This study adds to our understanding of the complex brain differences underlying attention-deficit/hyperactivity disorder. By connecting differences in brain structure to a key symptom of ADHD, it helps explain how biology gives rise to the cognitive and behavioral challenges associated with the condition. Further research in this area may lead to new ways to assess and address attention problems in ADHD.