Neuropsychology (2016) Feb;30(2):190-212
Can impaired working memory functioning be improved by training? – A meta-analysis with a special focus on brain injured patients
Juliane Weicker1,2, Arno Villringer1,2, & Angelika Thöne-Otto2
1 Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
2 University of Leipzig, Clinic of Cognitive Neurology, Leipzig, Germany
Objective: Deficits in working memory (WM) are commonly observed after brain injuries and cause severe impairments in patients’ everyday life. It is still under debate if training can enhance or rehabilitate WM in case of malfunction. The current meta-analysis investigates this issue from a clinical point of view. It addresses under which conditions and for which target group WM training may be justifiable. Method: Relevant WM training studies were identified by searching electronic literature databases with a comprehensive search term. A total of 103 studies, which added up to 112 independent group comparisons (N = 6113 participants), were included in the analysis. Results: Overall, WM training caused a moderate and long-lasting improvement in untrained WM tasks. Moreover, improvement of WM functioning led to sustainable better evaluation of everyday life functioning, however, effect sizes were small. Concerning transfer effects on other cognitive domains, long-lasting improvements with small effect sizes were observed in cognitive control and reasoning/intelligence. In contrast, small immediate, but no long-term effects were found for attention and long-term memory. Studies with brain injured patients demonstrated long-lasting improvements in WM functions with moderate to large effect sizes. A main moderator variable of intervention efficacy is the number of training sessions applied. Conclusion: WM training produces long-lasting beneficial effects which are strongly pronounced in patients with acquired brain injuries. This finding supports the application of WM training in clinical settings. To determine optimal training conditions, future studies must systematically investigate the characteristics of interventions as they are at present inevitably confounded.
Background and objective:
Patients with WM deficits report loss of concentration, distractibility and forgetfulness; they have difficulties following longer conversations, understanding complex written text passages, and they struggle to do things simultaneously (1, 2). Such impairments have been shown to affect the acquisition of new skills, academic achievement, the daily routine and resumption of work (3-5). Surprisingly, rehabilitation of WM is quite a recent endeavor starting as recently as in the late nineties. We focused on the clinical point of view to answer two essential questions: 1. Is WM training capable of causing long-lasting WM improvements especially in patients with WM deficits? 2. Is enhanced laboratory performance linked to the amelioration of everyday life so that training effects are of functional relevance for patients and their families? We combined the results of 103 studies and an overall number of N = 6113 subjects in a meta-analysis. For a better understanding and to improve the conditions of a successful treatment, various characteristics of WM training, e.g., type and duration of the intervention, were examined.
Transfer effects caused by WM training:
The performance on the training task itself increased dramatically during training. A more relevant point, however, is that WM training caused a long-lasting transfer effect on untrained WM tasks. Substantial changes in WM were accompanied by an increased quality of life and reduced disorder symptoms of patients with WM deficits. Concerning other cognitive domains, small but long-lasting improvements could be shown for reasoning and intelligence, as well as for cognitive control and executive functioning.
Influencing factors of WM efficacy:
Subject groups. Our analysis showed that all subject groups were able to improve their WM functions but a closer look at the effect sizes revealed that brain injured patients gained the most. This knowledge highlights the relevance of specific WM interventions in rehabilitation.
Type of the WM training. No differences in effectivity were found regarding the effectivity of general training mechanisms, although the most known training program „Cogmed“ seemed to produce the most robust effects. However, a confound between complexity of training tasks, training setting and subject groups has to be taken into account. In our experience, there are some characteristics which may be especially important for patients with WM impairment. While most programs modulate difficulty by increasing or decreasing the number of items to-be-remembered, for patients a much more fine-tuned adjustment of difficulty may be necessary to adapt exactly to their performance level (e.g. see (6) and Figure 1, WM training of Rehacom rehabilitation software).
Performance slope in the training intervention itself and Adaptivity. Training performance and automatic adjustment of difficulty had no influence on the effect of WM training. Thus, it seems to be the continuous challenge of WM tasks on an adequate level, rather than the progression within the training program, which indicates the efficacy of the training. Adaptivity to individual task performance does not seem to be mandatory if it is possible to challenge the subject’s WM system continuously in other ways.
Training duration. We observed a positive dose-response relationship, indicating that a longer period of training increases the WM training effect. It is, however, the number of training sessions, rather than the hours spent in training, which predicts efficacy. Our analysis showed that only interventions that included more than 20 training sessions were able to produce long lasting effects on WM functioning. However, it is still an open question whether high intensity or distributed training leads to larger training effects.
Figure 1. WM training task of Rehacom. Three cards are presented for a short time, next they are returned. The subject has to remember the cards and choose the right ones from the selection at the bottom. Difficulty is varied by the number of items, distractors, encoding time, and many more parameters that can be adjusted individually.
Importance of the study:
The presented meta-analysis suggests that WM training is effective. WM training does improve various aspects of WM functioning permanently and provides sustainable transfer effects to other cognitive domains, such as reasoning and intelligence, as well as cognitive control and executive functioning. Most importantly, the enhanced function of the system is reflected in the better performance of everyday life tasks and reduces disease-related symptoms in patients suffering from WM deficits. Patients with acquired brain injuries benefited strongly from the intervention which was shown by an increased WM performance immediately and at follow-up after several months. Thus, a fairly circumscribed specific intervention has an impact of functional and clinical relevance.
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- Crawford, S., Wenden, F. J., & Wade, D. T. (1996). The Rivermead head injury follow up questionnaire: A study of a new rating scale and other measures to evaluate outcome after head injury. Journal of Neurology Neurosurgery and Psychiatry, 60(5), 510-514.
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- Weicker, J., Hudl, N., Marichal, E., & Thöne-Otto, A. (2014). Training of working memory in brain injured patients and healthy elderly subjects – two randomized controlled trials. Zeitschrift für Neuropsychologie, 25(3), 199.
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