A landmark study from two decades ago claimed children with attention-deficit/hyperturnity disorder (ADHD) have brains that mature later. It shaped how we understand the disorder. Now it might just be data noise.
New research suggests that entire finding was a mirage.
What scientists thought was a biological hallmark of ADHD turns out to be something much more mundane. It reflects average differences between how boys’ and girls’ brains grow up. The earlier data probably just leaned too heavily on the development patterns of young boys.
It sounds like a simple correction. But the story behind it is messier.
A Story That Made Sense
Back in 2007 a team at the National Institute of Mental Health broke ground on the neurology of ADHD. They used MRI scans on 223 kids with the disorder and a control group.
Here’s what they saw. The cortex, the outer layer of the brain, thickens during childhood before thinning out later. In kids with ADHD that timeline was delayed.
Matthew Albaugh a clinical neuroscientist at UVM called the 2008 results “foundational.”
You see kids acting a little younger than their actual age. It just fits the behavior.
It told a good story. The study also showed earlier maturation in motor areas which seemed to explain hyperactivity. Everyone nodded along. The data matched the commonsense observation.
But science rarely stays that clean.
Sex Differences Shatter the Model
The new study published in PNAS on May 18 challenges that old narrative. Albaugh and his colleagues looked at the problem again using a much larger dataset.
They used data from the ABCD study which tracks over 11000 children across the US. First author Shannon O’Connor noted that initially the data looked just like the 2008 findings. Attention problems correlated with cortical thickness delays.
But then they added more variables.
O’Connor noticed a pattern. In previous ABCD analyses boys consistently showed a lower rate of cortical thin than girls. When the new team adjusted for this sex-specific developmental timing the link between ADHD and brain structure vanished completely.
That is what made the house of cards topple.
Previous studies only balanced boys and girls at a single point in time. As participants dropped out of those smaller studies the balance shifted. The data likely became skewed toward the slower cortical thinning typical of boys. When Albaugh’s team separated the data by sex the correlation disappeared in both groups. No relationship found.
The Replication Problem
This isn’t just about one study failing. It’s about the broader crisis in neuroscience replication.
Max Wiznitzer a pediatric neurologist at CaseWestern Reserve University called the new design strong. Albaugh’s team even double-checked their results using subsets of kids with clinical diagnoses. The outcome was the same. No distinct biological signature.
Powerful new datasets are doing something uncomfortable. Instead of strengthening old theories they are dismantling them. Many early findings were likely flukes.
Albaugh stressed that ADHD is still a real biological condition with strong genetic roots. That part hasn’t changed. What has changed is the hope that we can spot it via a simple MRI scan of cortical thickness. We can’t.
Wiznitzer argued this might be a relief rather than a tragedy. We never used cortical thickness for diagnosis or treatment anyway.
“If I put someone on medication and they get better who cares what their brain scan looks like?” he asked.
The improvement is the point. The biological signature might remain elusive. And maybe that’s fine. We treat the behavior not the pixel density of the cortex. The field now has to start looking elsewhere.
