Working memory deficits can be overcome: Impacts of training and medication on working memory in children with ADHD

Institution: University of York

Title: Working memory deficits can be overcome: Impacts of training and medication on working memory in children with ADHD

Researcher(s): J. Holmes, S. Gathercole, M. Place, D. Dunning, K. Hilyon, & J. Elliot

Program: Cogmed RM

Published: Applied Cognitive Psychology

Funding: The research was supported by grants from the British Academy and the Economic and Social Research Council. Training program, investigator training, and technical support provided by Cogmed. No funding provided by Cogmed.


View a presentation about this study by Dr. Joni Holmes.

Working memory is the cognitive system responsible for the temporary storage and manipulation of information and plays an important role in both learning and focusing attention. Considerable research has documented that many children and adults with ADHD have working memory deficits and that this contributes to difficulties associated with the disorder. For an excellent introduction to the role of working memory deficits in ADHD, visit aboutkidshealth.ca.

A simple example illustrates the importance of working memory for particular academic tasks. Try adding 3 and 9 in your head. That was probably easy for you. Now try adding 33 and 99. That was probably more difficult. Finally, try adding 333 and 999. This is quite challenging for most adults even though each calculation required is trivially easy. The challenge occurred because you need to store extra information and this taxed your working memory. If your working memory capacity was exceeded, you could not complete the problem successfully.

This simple problem also illustrates the difference between short-term memory and working memory. Short-term memory simply involves retaining information in mind for short periods of time, e.g., remembering that the problem you need to solve is 333+999.

Working memory, in contrast, involves mentally manipulating – or ‘working’ with – retained information and comes into play in a wide range of learning activities. For example, to answer questions about a science chapter, a child not only has to correctly retain factual information but must mentally work with that information to answer questions about it. Thus, when a child’s working memory capacity is low relative to peers, academic performance is likely to be compromised in multiple areas.

Because working memory deficits play an important role in the struggles experienced by many individuals with ADHD, it is important to consider how different interventions address this aspect of the disorder. In this study, the authors were interested in comparing the impact of Working Memory Training and stimulant medication treatment on the working memory performance of children diagnosed with ADHD.

Participants were 25 8-11 year-old children with ADHD (21 boy and 4 girls) who were being treated with stimulant medication. Children’s memory performance was assessed on 4 occasions using the Automated Working Memory Assessment (AWMA), a computerized test that measures verbal short-term memory, verbal working memory, visuo-spatial short-term memory, and visuo-spatial working memory.

At time 1, the assessment was conducted when children had been off medication for at least 24 hours. The second assessment occurred an average of 5 months later and when children were on medication. The third assessment occurred after children had completed 5 weeks of Cogmed Working Memory Training using the standard training protocol (see below). The final assessment occurred approximately 6 months after training had ended. This design enabled the researchers to make the following comparisons:

– Working memory performance on medication vs. off medication (T1 vs. T2)
– Working memory performance on medication vs. after training (T2 vs. T3)
– Working memory performance immediately after training ended vs. 6 months following training (T3 vs. T4)

This final comparison provided information on whether any benefits provided by the training had endured.

In addition to measuring short-term memory and working memory at each time point, measures of IQ were collected at times 1, 2, and 3.

Working Memory Training
Working memory training was conducted using the standard Cogmed training protocol with each child completing 20-25 training sessions within a 25 day period. The training requires the storage and manipulation of sequences of verbal, e.g., repeating back a sequence of digits in reverse order, and/or visuo-spatial information, e.g., recalling the location of objects on different portions of the computer screen.

Difficulty level is calibrated on a trial by trial basis so the child is always working at a level that closely matches their performance. For example, if a child successfully recalled three digits in reverse order, on the next trial he had to recall four. When a trial was failed, the next trial was made easier by reducing the number of items to be recalled. This method of ‘adaptive training’ is thought to be a key element because it requires the child to ’stretch’ their working memory capacity to move through the program.

Results
Impact of Short-Term Memory and Working Memory
Medication vs. no medication – When tested on medication, children showed better visuo-spatial working memory relative to when they were tested off medication. However, no improvement was found for verbal short-term memory, verbal working memory, or visuo-spatial short-term memory.

Performance on medication vs. performance after working memory training – Cogmed Working Memory Training led to significant gains in all four memory scores. Thus, there was evidence that working memory training led to greater gains in working memory that medication treatment alone. On all areas of memory assessed, the average score of participants had moved from below average to within the average range.

Performance 6 months after training ended – Training gains in 3 of the 4 memory components – all but visuo-spatial short-term memory – remained significant 6 months after training had ended and there was little indication of any decline in children’s performance. Thus, the benefits evident immediately following training had largely persisted.

Impact on IQ
IQ results on and off medication were equivalent. Likewise, there was no indication that working memory training was associated with any increase in children’s IQ results. Thus, the benefits of training were restricted to children’s performance on the memory tasks.

Summary and Implications
Results from this study indicate that working memory training yields greater benefits in working memory for children with ADHD than are provided by stimulant medication treatment. Furthermore, memory gains following training persist for a significant period.

Because adequate working memory functioning is critically important for children’s academic success, these are encouraging findings as they suggest that intensive training can ameliorate deficits in this important executive function. The absence of training benefits on IQ suggests that the benefits of training may be limited to working memory specifically, although it should be noted that other working memory training studies have reported benefits on particular aspects of intelligence. Thus, the possible impact of working memory training on IQ requires further study.

However, it is important not to over interpret the results from this study. While it is tempting to regard this as a comparison of medication treatment and working memory training for ADHD, and to view the results as indicating the superiority of the latter, this would be an erroneous interpretation. The constellation of difficulties that comprise ADHD for many children extend significantly beyond working memory deficits, and this study did not examine a number of other important outcomes.

For example, it provides no information on the relative benefits of medication and working memory training on children’s attention, hyperactivity, other behavior problems, and academic performance. Even though other studies of working memory training have found benefits in several of these areas, adding assessments of these critical outcomes to the current study would have strengthened it. This criticism is not intended to discount the important results obtained, but to instead provide an appropriate context for evaluating these interesting findings.

It is also the case that the study was limited by restricting the assessment of working memory to computerized measures of this capacity, even though validated parent and teacher rating scale measures of working memory are available. Incorporating such measures into the study would have provided a more comprehensive of children’s memory functioning at each assessment point.

Although these represent important study limitations, the results provide additional evidence that intensive working memory training can yield enduring benefits in this key executive function. Because the benefits provided by training enhance those provided by medication, it also suggests that working memory training may be a useful complement to existing evidence-based interventions for ADHD, particularly for children whose working memory functioning is impaired to begin with.