Currently, more than 6 million children in the United States, or 11% of all children aged 4 to 17, have received attention-deficit hyperactivity disorder (ADHD) diagnoses. The disorder is characterized by impulsiveness, hyperactivity and difficulty paying attention. Kids with ADHD have been shown to struggle in school, have trouble with friendships and be more prone to injury than other children their age. At present, diagnosing ADHD is quite subjective and unstandardized, with different thresholds of behaviour used to make the diagnosis in different places.
For instance, according to the U.S. Centers for Disease Control and Prevention, in 2011, 7.3% of all children in California had at some point been diagnosed with ADHD, making the state one of five nationwide with diagnosis rates below 8 percent among children. At the other end of the spectrum, six states had rates above 15 percent. Now, a study from researchers at Stanford University has shown interactions between three brain networks that help people pay attention are weaker than normal in children with ADHD. The team state that the degree of weakness imaged in their study was directly correlated to the severity of the children’s inattention symptoms.
Previous studies show that ADHD is associated with widespread but often subtle alterations in multiple brain regions affecting brain function. Studies using functional magnetic resonance imaging (fMRI) report altered intrinsic connectivity within and between networks including the dorsal and ventral attention, salience, and default mode networks. Structural connectivity studies are less common and the extent to which these functional alterations are underpinned by deep-seated structural effects remains to be determined. Earlier studies from the group proposed that poor coordination between three brain networks, namely the salience network, central executive network, and default mode network, could underlie a variety of psychiatric and neurologic problems. The current study shows that children with ADHD had weaker interactions between these networks than children without the condition with brain scans able to distinguish children who had ADHD from those who did not.
The current study focused on the salience network, which is a set of brain regions that work together through well-synchronized neural activity to help decide where one’s attention should be directed. The lab explain that 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. They go on to add that the salience network helps people stop daydreaming or thinking about something that happened yesterday so they can focus on the task-at-hand. Results show that that this network’s ability to regulate interactions with other brain systems is weaker in kids with ADHD.
The group studied functional magnetic resonance imaging brain scans from 180 children, half with ADHD and half without. The scans were taken when the children were awake and resting quietly, the children were also assessed for ADHD symptoms using traditional diagnostic methods. The team state that all study data were obtained from the ADHD-200 Consortium, an opensource database of fMRI scans and other clinical characteristics of hundreds of children with or without ADHD. They go on to stress that the new findings are noteworthy in part because they were replicated in independent data sets from three different sites in New York, Portland and Beijing that contributed to the consortium.
Next, the researchers scored each brain scan according to the synchronization between the salience network and two other related brain networks, namely, 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. The lab explain that 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. Data findings show that multivariate classifiers based on cross-network coupling measures differentiated children with ADHD from control subjects with high classification rates (72% to ~83%) for each dataset.
The team surmise that their study demonstrates that the global medical community can develop a very robust biomarker based on functional neuroimaging to reliably diagnose children with ADHD. They go on to add that it would be very beneficial to have a diagnostic measure that uses more objective and reliable measures, not just non-medical based assessments of behaviour. For the future, the researchers state that more work is needed to explore whether fMRI can also differentiate between the brains of children with ADHD and those with other psychiatric or neurodevelopmental conditions. They go on to conclude that answering that question is an important aspect of determining whether brain scans could become a practical component of ADHD diagnosis.