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). Moreover, 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 two 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.Lack of credible evidence of efficacy is increasingly highlighted in popular media.