Researchers in the US found that children with attention-deficit hyperactivity disorder (ADHD) showed more inconsistent reaction times when doing short term memory exercises compared to peers of the same age who did not have the disorder.
The study was the work of associate professor Dr Julie Schweitzer of the M.I.N.D. Institute & Department of Psychiatry and Behavioral Sciences, University of California-Davis, and colleagues, and is published in the journal Child Neuropsychology.
Schweitzer told the press that:
“We think poor working memory is a characteristic present in many children and adults with ADHD.”
She said the study helps to explain why “working memory may be fine at one moment and poor at another, just as one day a child with ADHD seems to be able to learn and focus in class and on another day seems distracted and not paying attention.”
About 4.4 million American children aged 4 to 17 have been professionally diagnosed with ADHD in the US, according to estimates from the US Centers for Disease Control and Prevention (CDC). And in 2003, the parents of 8 per cent of schoolchildren said their child had the disorder.
Schweitzer and colleagues say their results support the idea that inability to respond consistently while doing a task where he or she has to use working memory is what impairs the working memory of a child with ADHD.
Some studies have already shown that children with ADHD vary widely in how fast they can complete tasks that demand use of working memory compared to children who develop normally. Others have suggested that children with ADHD might have slower response times.
For this study the researchers used more finely tuned statistical tools to find out if ADHD reaction times are faster, slower, or whether the underlying process is less straightforward.
They found that children with ADHD were mostly responding at the same rate as their normally developing counterpars, but showed a higher rate of very slow responses.
For the study the researchers gave 25 children with ADHD and 24 controls (children without ADHD who were developing normally) a series of computer based mental arithmetic exercises. For instance, they were asked to add a number on one screen to a number on another screen without using pencil and paper, and they had to decide whether a given sum was right or not.
The children did the exercises over a number of sessions, at different speeds and different levels of difficulty.
Lead author Wendy Buzy, who was a graduate student at the time said:
“We found that the children with ADHD were much less consistent in their response times.”
She said that while the ADHD children’s responses were just as accurate as the non-ADHD children, more of their responses took longer.
The study used a different approach in the analysis. Previous studies compared the range of response times and average response times for children with ADHD and controls; but in this study the researchers used more sophisticated tools so they could compare variation in reaction times within and between individuals, as well as within and between groups.
Schweitzer said they also found that:
“Higher levels of hyperactivity and restlessness or impulsivity correlated with slower reaction times.”
This study has triggered another member of Schweitzer’s team, postdoctoral fellow Catherine Fassbender, to start looking at fMRI brain images of ADHD children to examine variability in response time during a working memory task.
Schweitzer also wants to investigate treatments that might help to reduce the variability in use of working memory.
“Improving consistency in how children with ADHD respond to the environment should help them generalize what they learn in clinical interventions improving their skills across situations,” she explained.
“Intra-Individual Variability Among Children with ADHD on a Working Memory Task: An Ex-Gaussian Approach.”
Buzy, Wendy M, Medoff, Deborah R, Schweitzer, Julie B
Child Neuropsychology 2009
Sources: UC Davis Health System.
Written by: Catharine Paddock, PhD