Working memory (WM) 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 WM deficits and that this contributes
to difficulties associated with the disorder. For an excellent introduction
to the role of WM deficits in ADHD, visit http://research.aboutkidshealth.ca/teachadhd/abc/chapter3#SUBTITLE3
A simple example illustrates the importance of WM for particular academic
tasks. Try adding 3 and 9 in your head. That was probably easy
for you. Now trying 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 information - the sum of
3+9 in the one's column and then ten's column - as you process the remaining
part of the problem, i.e., 3+9 in the hundred's column, and this taxed your
WM. If your WM capacity was exceeded, you could not complete the problem
This simple problem also illustrates the difference between short-term memory
(STM) and WM. 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 WM capacity is low relative to peers,
academic performance is likely to be compromised in multiple areas.
Because WM 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. This was the issue addressed
in a recenlty published study [Holmes et. al., (2009). Working memory deficits can be overcome: Impacts
of training and medication on working memory in children with ADHD, Applied Cognitive Psychology
Published Online: Jun 22 2009 5:36AM DOI: 10.1002/acp.1589.] in which
the authors were interested in comparing the impact of Working Memory Training
and stimulant medication treatment on the WM performance of children diagnosed
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
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:
- WM performance on medication vs. off medication (T1 vs T2)
- WM performance on medication vs. after training (T2 vs. T3)
- WM 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 STM and WM at each time point, measures of IQ were
collected at times 1, 2, and 3.
- Working Memory Training
WM 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 WM capacity to move through the program.
- Impact of Short-Term Memory and Working
Medication vs. no medication - When tested on medication, children showed
better visuo-spatial WM relative to when they were tested off medication.
However, no improvement was found for verbal STM, verbal WM, or visuo-spatial
Performance on medication vs. performance after WM training - Cogmed WM Training
led to significant gains in all four memory scores. Thus, there was
evidence that WM training led to greater gains in WM 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 STM - 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 WM 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.
Results from this study indicate that WM training yields greater benefits
in WM for children with ADHD than are provided by stimulant medication treatment.
Furthermore, memory gains following training persist for a significant period.
Because adequate WM 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 WM specifically, although it should be noted that other WM training
studies have reported benefits on particular aspects of intelligence.
Thus, the impact of WM 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 WM 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 WM deficits, and this study did not examine a number of other important
For example, it provides no information on the relative benefits of medication
and WM training on children's attention, hyperactivity, other behavior problems,
and academic performance. Even though other studies of WM 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
and it would not be surprising if medication treatment were to have greater
impact in other important areas.
It is also the case that the study was limited by restricting the assessment
of WM to computerized measures of this capacity, even though validated parent
and teacher rating scale measures of WM 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 WM training can yield enduring benefits
in this key executive function. Because the benefits providing by training
enhance those provided by medication, it also suggests that WM training may
be a useful complement to existing evidence-based interventions for ADHD,
particularly for children whose WM functioning is limited to begin with.