Working memory training
Working memory training is endeavor intended to improve a person's working memory. Working memory is a central intellectual faculty, linked to IQ, ageing, and mental health. It has been claimed that working memory training programs are effective means, not only for treating attention-deficit/hyperactivity disorder (ADHD) and other childhood disorders, but to improve intelligence and school attainment in all children and adults. Empirical tests of these claims, however, suggest that the effects are at best "variable" and not-significant over all.
Working memory (WM) is the system which holds multiple pieces of transitory information in the mind - information that is needed for different tasks right now. WM is usually assessed by determining the number of pieces of information a person can hold in mind. For example, a person might be asked to listen to a series of digits and letters, sort them into order in mind, and then recall the sorted list aloud. The longest set of characters that can reliably be manipulated and recalled is the working memory capacity.
The capacity of working memory differs between people: a person able to recall 8 instructions has a greater working memory capacity than someone who can only recall a series of five. Numerous scientific studies have linked working memory capacity with strength in other fundamental cognitive abilities, including attention and intelligence.  Conversely, poor working memory is assumed to be one of the core deficits in ADHD as well as a number of learning disabilities. 
The concept of working memory became widely accepted and its importance better understood across the 1970s. At this time, a number of attempts to improve working memory were also initiated. For instance, in one case, a college student practiced repeating numbers that were read to him aloud for an hour each day.  He did this three to five times a week for twenty months until he could repeat as many as 79 digits. While his capacity on this trained task had improved, his working memory: the ability to store information, as described above had not. This was most clearly demonstrated when, asked to repeat letters instead of numbers, this same student with over 320 hrs of practice at recalling digits could recall only six letters at a time: a normal to below average performance. The effect of the training was not to improve the working memory system but to change the information being stored: the student had learned multiple methods of grouping numbers and relating them to similar figures already in his long term memory. In reality, his working memory capacity had not increased. This study and others like it contributed to the prevailing assumption in the scientific community that working memory is a set characteristic that cannot be improved.
Renewed claims for improving working memory
Studies continued to demonstrate that learning tasks intended to enhance episodic memory could lead to improved strategies, even in the elderly but did not demonstrate enhanced working memory capacity. However, the 1990s and 2000s also saw a resurgence of claims to improve working memory, treat clinical disorders such as ADHD, and enhance IQ.
Examples include the computerized working memory training program market by the Cogmed company  In 2002 Klingberg presented results from a very small sample (14) of children with ADHD. In a follow-up study of 53 children with ADHD, he and co-authors concluded "WM can be improved by training in children with ADHD". However, while tests immediately following the training showed reasoning and attention span improvements in the trained group compared to the control group, tests three months later showed no effect of the training. At both the immediate and 3-month later tests, there was no difference between the control and training groups in the number of head movements (a measurement of inattention), and the number of head movements was not reduced in either group, casting doubt on any treatment aspects linked to ADHD 
Subsequent analyses of the program by Georgia Institute of Technology researchers who reviewed the world's literature on WMT concluded that "the results are inconsistent" and that studies had "inadequate controls" as well as "ineffective measurement of the cognitive abilities of interest.". Despite this null long-term results of the 2005 study, Klingberg's company Cogmed sold the program through licensed medical doctors and psychologists.
In 2012, a systematic meta-analytic review was undertaken. Stringent criteria for inclusion ensured that all studies were either randomized controlled trials or quasi-experiments. All studies had to have a treatment and a treated or untreated control group. By this time, some twenty-three studies met these criteria, including both clinical samples typically developing children and adults. The results closely replicated the original finding by Ericcson et al. (1980): There were short-term improvements in practiced skills. But there was no convincing evidence for transfer or generalisation effects (indicating improved capacity). This study of the world-literature "cast doubt on both the clinical relevance of working memory training programs and their utility as methods of enhancing cognitive functioning in typically developing children and healthy adults."
Other researchers from universities around the world have also studied the effects of the Cogmed company's training on children with attention issues. Among them are NYU, and the University of York. In addition, many researchers are now exploring the use of working memory training for various new applications, with studies having been completed or launched on normal and aging adults, pediatric cancer survivors, and victims of stroke and traumatic brain injury.
In the February 2009 edition of Science, Klingberg and colleagues, led by F McNab, claimed that adaptive span training had led to changes in dopamine D1 and D2 receptors. In the same study, tests of "far transfer" - whether or not the skills in one test applied to very different intelligence-related skills - were made. The results were not reported. (see supporting online materials). Moreoever, research at the Wallenberg Neuroscience Center in Sweden indicates that working memory training may decrease hippocampal neurogenesis. When experimental medical scientists trained adult male rats in a working memory task for 4 or 14 days, rats trained for 2-weeks had fewer newborn hippocampal neurons than those that were only trained for 4 days. The report suggests that increased stress, caused by an intense training of working memory, can reduce the production of hippocampal neurons.
In summary, despite numerous, well-powered attempts to show increased capacity of working memory as a result of training, the totality of results suggest no significant effects in either clinical or normal groups.
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