Interactions between three attention-related brain networks are weaker in children with attention-deficit hyperactivity disorder (ADHD), according to a new study from the Stanford University School of Medicine. In fact, the weaker the connections, the more severe the symptoms of inattention.
For the study, the researchers focused on the salience network, a set of brain regions that work together to help decide where one’s attention should be directed. In most children, this network can assess the importance of internal and external events, and then regulate other thoughts to focus attention in the right place.
“A lot of things may be happening in one’s environment, but only some grab our attention,” said Vinod Menon, Ph.D., a professor of psychiatry and behavioral sciences and the study’s senior author.
“The salience network helps us stop daydreaming or thinking about something that happened yesterday so we can focus on the task at hand. We found that this network’s ability to regulate interactions with other brain systems is weaker in kids with ADHD.”
Currently, diagnosing ADHD is quite subjective, with different measures of behavior used to make the diagnosis in different areas.
For example, according to the U.S. Centers for Disease Control and Prevention, in 2011, 7.3 percent of California children had been diagnosed with ADHD, making the state one of five nationwide with diagnosis rates below eight percent among children. At the other end of the spectrum, six states had rates above 15 percent.
“It would be very beneficial to have a diagnostic measure that uses more objective and reliable measures, not just clinical and parental assessments of behavior,” said Weidong Cai, Ph.D., an instructor in psychiatry and behavioral sciences and the study’s lead author.
“This study also demonstrates that we can develop a very robust biomarker based on functional neuroimaging to reliably differentiate children with ADHD from other kids.”
The researchers analyzed the functional magnetic resonance imaging (fMRI) brain scans of 180 children, half with ADHD and half without. The scans were taken when the children were awake but resting quietly. The children were also assessed for ADHD symptoms using traditional diagnostic methods.
The team rated each brain scan based on the synchronization between the salience network and two other related brain networks: the default mode network, a set of brain regions that directs self-referential activities such as daydreaming; and the central executive network, which manipulates information in working memory.
To focus one’s attention, the salience network must turn down the activity of the default mode network while turning up the activity of the central executive network.
The research team had previously proposed that poor coordination between these three brain networks could underlie a variety of psychiatric and neurologic problems, including depression, schizophrenia, brain injury, autism, and drug addiction.
The findings reveal that kids with ADHD had weaker interactions between these networks than children without the condition. The difference was large enough that brain scans could distinguish kids who had ADHD from those who did not.
Among children with ADHD, worse scores on clinical tests of inattentiveness were linked with weaker interactions between the three brain networks.
“These three brain networks come up over and over in pretty much every cognitive task we ask subjects to do,” said Menon, who holds the Rachael L. and Walter F. Nichols, M.D., Professorship. “They are critical for information processing and attending to stimuli in the environment.”
More research is needed to find out whether fMRI can also differentiate between the brains of children with ADHD and those with other psychiatric or neurodevelopmental conditions, the researchers said. Gaining a better understanding of this subject would be an important aspect of determining whether brain scans could become a practical component of ADHD diagnosis.
The study is published online in the journal Biological Psychiatry.