Working memory (WM) capacity is the ability to retain and manipulate information during a short period of
time. This ability underlies complex reasoning and has generally been regarded as a ®xed trait of the
individual. Children with attention de®cit hyperactivity disorder (ADHD) represent one group of subjects
with a WM de®cit, attributed to an impairment of the frontal lobe. In the present study, we used a new
training paradigm with intensive and adaptive training of WM tasks and evaluated the effect of training with
a double blind, placebo controlled design. Training signi®cantly enhanced performance on the trained WM
tasks. More importantly, the training signi®cantly improved performance on a nontrained visuo-spatial WM
task and on Raven's Progressive Matrices, which is a nonverbal complex reasoning task. In addition, motor
activity ± as measured by the number of head movements during a computerized test ± was signi®cantly
reduced in the treatment group. A second experiment showed that similar training-induced improvements on
cognitive tasks are also possible in young adults without ADHD. These results demonstrate that performance
on WM tasks can be signi®cantly improved by training, and that the training effect also generalizes to
nontrained tasks requiring WM. Training improved performance on tasks related to prefrontal functioning
and had also a signi®cant effect on motor activity in children with ADHD. The results thus suggest that WM
training potentially could be of clinical use for ameliorating the symptoms in ADHD.