Working Memory
Working memory is a key cognitive function required for many types of mental activities. It is
defined as the ability to actively retain information for a short period of time and to be able to
use this information in our thinking. One way of measuring working memory capacity is by testing
how many numbers a person is able to recite after hearing them one time. Working memory is
used on a daily basis for activities such as remembering instructions, solving problems and paying
attention "in order to be able to focus on what we are doing right now.” Problems with working
memory are often experienced as an inability to concentrate, such as staying focused while
reading. Children with working memory deficits often forget what they are supposed to do next,
which makes it difficult to follow instructions and complete tasks.

Working memory depends on the successful functioning of the frontal lobe dopamine system.
Recently, researchers and clinicians have drawn attention to the fact that problems with
working memory are common in cases of ADHD as well as in cases where subjects have severe
difficulties concentrating. The same applies to more general learning disabilities in terms of
problems associated with specific school subjects that do not depend on lack of intelligence or
physical/psychological illness. It has been demonstrated that such learning disabilities can be
directly connected to deficiencies in working memory (Gathercole and Pickering, 2000).
Individuals can have a reduced working memory capacity without fulfilling the criteria for any
specific diagnosis.

          
Research
The first study on Cogmed Working Memory Training was conducted in 2001 and included
children (ages 7-13) diagnosed with ADHD (Klingberg et al. 2002). This study was very
successful and showed large results on improving working memory and problem solving tasks.
Since the number of children in the study was small, a larger study was undertaken to increase
the statistical robustness of the results and to study the effects of training in day-to-day life
with sustainability. It was carried out at four clinics in Sweden (Klingberg et al., 2005).
The study was designed as a random, placebo-controlled, double-blind study. Just as the first
study, two different varieties of the training program were compared: one with more difficult
tasks and one with easier tasks (=control). Assessments of symptoms and neuropsychological
tests were done before, after and three months following the training sessions. When the
neuropsychological testing was completed after training, it was shown that the treatment group
had significantly improved compared to the control group for tasks involving working memory. In
addition, they had improved impulse control and problem-solving ability.  Ninety-percent of the
effects remained at a 3-month follow-up. Parental assessments showed a significant decrease of
symptoms related to concentration difficulties and hyperactivity. The combined assessments by
parents and teachers showed a significant decrease in concentration difficulties. The results of
the second study confirmed findings from the first study relative to improvement on
neuropsychological tests.  In addition, there was improvement when symptoms were evaluated in
relation to concentration and hyperactivity.

Strokes that affect the frontal lobe and more serious head injuries can also result in impaired
working memory (Robertson and Murre, 1999). Smaller scientific studies on Cogmed Working
Memory Training have been done with adults with and without brain injuries. The results have
been positive: improvements in working memory and attention have been measured with neuro-
psychological tests and rating scales (Westerberg, 2007). Another study (Olesen, Westerberg
and Klingberg, 2004) showed increased brain activity in the areas of the brain associated with
working memory. Non-scientific evaluations of training have also been performed on other
groups: children with ABI (Acquired Brain Injury), children with epilepsy and adults with ADHD.
They all point in the same direction – working memory can be improved and will show results on a
day-to-day basis.

In 2005, a study was conducted with children in special education classes. Forty-four children
were included on the basis of attending special education groups and having deficits in working
memory. About half of the children were diagnosed with ADHD. The results have not yet been
published. However, at a presentation at CHADD’s annual conference in October 2006, Dr.
Torkel Klingberg reported there were significant improvements in reading comprehension and
math along with improvements on neuropsychological tests measuring working memory.
There have also been a number of children who have gone through training without a specific
diagnosis but have working memory deficits. Taken together, these evaluations all point in the
same direction – a known impairment of working memory is the key to successful training.  Which
diagnosis reveals working memory deficits does not seem to be a factor in the outcome of
training.  If there is an impairment of working memory you are able to initiate training and 85%
of those who train will show benefits in daily life.

Klingberg T, Fernell E, Olesen P, Johnson M, Gustafsson P, Dahlström K, Gillberg CG, Forssberg
H, Westerberg H (2005)
Computerized Training of Working Memory in Children with ADHD – a Randomized, Controlled,
Trial.
J American Academy of Child and Adolescent Psychiatry 44 (2):177-186.
Link to abstract

Klingberg T, Forssberg H, Westerberg H (2002)
Training of working memory in children with ADHD.
J Clin Exp Neuropsych 24:781-791

Olesen P, Westerberg H, Klingberg T (2004)
Increased prefrontal and parietal brain activity after training of working memory.
Nature Neuroscience 7:75-79
Link to abstract

Westerberg H, Jacobaeus H, Hirvikoski T, Clevberger P, Ostensson J, Bartfai A, Forssberg H,
Klingberg T (2003)
Computerized working memory training - a method of cognitive rehabilitation after stroke.
Proceeding from the Conference on Stroke Injury, Stockholm, 2003

Westerberg H, Hirvikoski T, Forssberg H, Klingberg T (2004)
Visuo-spatial working memory: a sensitive measurement of cognitive deficits in ADHD.
Child Neuropsychology 10 (3) 155-61