Thursday, April 17, 2014

Open Letter to Nature: Working memory improves with persistent training



Enhancing cognitive function has become a popular news topic. As a result of the proliferation of scientific inquiry into the area, commercial vendors have capitalized on the popularity of “brain training” (examples include the Nintendo© Brain Age and Big Brain Academy software. In the June 10 issue of Nature, Owen et al. examined whether performing a variant of the training tasks in these programs would improve cognitive performance, and concluded that training on these tasks did not transfer to other tasks for which participants were not trained. Here, we suggest that the null findings reported by Owen et al. are the consequence of participants’ casual, rather than consistent, engagement in their training tasks. We present data illustrating that persistent engagement in cognitive training within a controlled environment can lead to improved cognitive functioning that endures over time.

To the Editor: In response to a June 2010 Nature article by Owen et al., we suggest that the null findings are the consequence of participants’ casual, rather than consistent, engagement in their training tasks.1 We present data illustrating that persistent engagement in cognitive training within a controlled environment can lead to improved cognitive functioning that endures over time.

Owen et al. recruited participants for three groups: two experimental groups and a control group. The first experimental group worked on six training tasks emphasizing “reasoning, planning, and problem-solving abilities.” A second experimental group completed tests normally given to assess a wide range of cognitive abilities like short-term memory, attention, visuospatial attention, and mathematics. The control group looked up answers to trivia questions in lieu of any cognitive training. All participants completed several pre- and posttraining assessments that measured broad cognitive abilities and were used to evaluate change over the course of the 6-week training. The authors reported only very small changes in the pre- and posttraining scores for the experimental groups (an average of 3% increase), whereas the control group participants increased their pre- and posttraining scores an average of 2%. For this reason, the authors concluded that these computer-training programs do not improve cognitive functioning in healthy participants beyond the tasks in the programs.

Figure 1: (a) Mean difficulty reached for n-back training over 10 sessions. (b) Verbal working memory score by condition and assessment period. For the experimental group, verbal working memory was significantly greater in posttraining and follow-up than in pretraining, both ps<0.01, with large effect sizes (Cohen’s d = 0.82 and 0.83). There was no significant difference between pretraining and posttraining or between pretraining and follow-up for the control group (effect sizes: ds = .30 and 0.15, respectively). The experimental group improved more at posttest and follow-up compared to the control, which was supported by a significant interaction, p<0.01.

Important methodological details of the Owen et al. study are the duration and intensity of the training: the minimum duration of training for inclusion in the study was a total of 20 minutes over 6 weeks, and the mean training duration was only 4 hours. This relatively short training period contrasts with prior work showing successful training and transfer of brain training exercises, which generally consist of roughly 20 hours of training over a 5- to 6-week period2–8. To put this in context, 4 hours of cardiovascular fitness training over 6 weeks would likely yield minimal health benefits; there is no reason to believe that 4 hours of brain fitness training would be any more effective at improving cognitive ability. The short period of cognitive training Owen et al. used raises the question: did they really put brain training to the test?

We re-evaluated Owen et al.’s claim that brain training does not improve cognitive functioning in healthy adults. In our study, 47 participants trained for 20 hours over 6 weeks on a battery of performance-adaptive cognitive training tasks designed to enhance working memory functioning. Figure 1a plots the increase in performance on one of the training tasks (n-back) across the 10 training sessions. Figure 1b illustrates the degree to which training transferred to an ostensibly different (and untrained) measure of verbal working memory compared to a no-contact control group. Not only did training significantly increase verbal working memory, but these gains persisted 3 months following the cessation of training! These findings are in stark contrast to those of Owen et al., suggesting that prolonged involvement in demanding cognitive training can indeed yield improvements in general cognitive functioning. As with physical fitness training, cognitive training can be effective with persistent use of sufficiently demanding training tasks; casual use of cognitive training software is likely to be ineffective.


In our study, 93 participants were randomly assigned to either the experimental or no-contact control group. All participants completed a 4-hour assessment battery of memory and language tasks. Experimental participants subsequently completed 20 1-hour training sessions across 4 to 7 weeks; control participants had no experimental contact during this time. Both groups returned to the lab for assessment immediately following training and again 3 months later. Working memory training gains were calculated by (1) examining increases in training performance over the 20 hours of training and (2) comparing the data from the three assessments of the control and experimental groups.

Jeffrey S. Chrabaszcz[1], Michael R. Dougherty[2], Sharona M. Atkins[2], J. Isaiah Harbison[1], Jared M. Novick[1], Scott A. Weems[1], Erika K. Hussey [2], Susan Teubner-Rhodes[2], Alexei Smaliy[1], Carrie K. Clarady[1], Ryan P. Corbett[1], Barbara H. Forsyth[1], and Michael F. Bunting[1]

[1]University of Maryland Center for Advanced Study of Language, College Park, Maryland 20742

[2]Department of Psychology, University of Maryland, College Park, MD 20742


1 Owen, A. M., Hampshire, A., Grahn, J. A., Stenton, R., Dajani, S., Burns, A. S., Howard, R. J., & Ballard, C. G. (2010, June 10). Putting brain training to the test. Nature; DOI 10.1038/nature09042 .

2 Olesen P. J., Westerberg, H., & Klingberg, T. (2004). Increased prefrontal and parietal activity after training of working memory. Nat. Neurosci. 7, 75–79.

3 Klingberg, T., Forssberg, H., & Westerberg, H. (2002). Increased brain activity in frontal and parietal cortex underlies the development of visuospatial working memory. J. Cognitive Neurosci. 14, 1–10.

4 Klingberg, T., Fernell, E., Olesen, P., Johnson, M., Gustafsson, P., Dahlström, K., Gillberg, C.G., Forssberg, H., & Westerberg, H. (2005). Computerized training of working memory in children with ADHD—A randomized, controlled trial. J. Am. Acad. Child Adol. Psy. 44, 177–186.

5 Jaeggi, S. M., Buschkuehl, M., Jonides, J., & Perrig, W. J. (2008). Improving fluid intelligence with training on working memory. P. Natl. Acad. Sci. 105, 6829–6833.

6 Temple, E., Poldrack, R. A., Protopapas, A., Nagarajan, S., Salz, T., Tallal, P., Merzenich, M. M., & Gabrieli, J. D. (2000). Disruption of the neural response to rapid acoustic stimuli in dyslexia: Evidence from functional MRI. P. Natl. Acad. Sci. 97, 13907–13912.

7 Mahncke, H. W., Connor, B. B., Appelman, J., Ahsanuddin, O. N., Hardy, J. L., Wood, R. A., Joyce, N.A., Boniske, T., Atkins, S. M., & Merzenich, M. M. (2006). Memory enhancement in healthy older adults using a brain plasticity-based training program: A randomized, controlled study. P. Natl. Acad. Sci. 103, 12,523–12,528.

8 Thorell, L. B., Lindqvist, S., Bergman, S., Bohlin, G., & Klingberg, T. (2008). Training and transfer effects of executive functions in preschool children. Developmental Sci. 11, 969–976.