Cognitive training interventions for dementia and mild cognitive impairment in Parkinson’s disease

Abstract

Plain language summary

Cognitive training interventions for dementia and mild cognitive impairment in Parkinson’s disease

Review question

We wanted to know whether cognitive training interventions are effective in improving cognition (thinking) in people with Parkinson’s disease dementia or mild cognitive impairment.

Background

Approximately 60% to 80% of people with Parkinson’s disease (PD) develop some degree of cognitive impairment, meaning that they may have difficulties with thinking and reasoning, memory, language, or perception. If these difficulties are severe enough to affect the person’s ability to carry out daily activities, then the person is said to have Parkinson’s disease dementia (PDD). If someone has cognitive problems but their daily activities are not significantly affected, then he or she is said to have mild cognitive impairment in Parkinson’s disease (PD‐MCI). Cognitive training involves practising cognitive skills such as memory, attention, and language through specific tasks. It may be able to help people with PDD or PD‐MCI maintain better cognitive skills.

What we did

This review examined whether cognitive training is effective in improving outcomes such as overall cognitive skills (‘global cognition’), memory, attention, or ability to carry out daily activities in people with PD and either dementia or MCI. We searched the medical literature for research studies that compared people receiving a cognitive training intervention to those not receiving the intervention (a ‘control group’). We only included studies in which the decision about whether or not someone received the cognitive training intervention was made randomly; such studies are called randomised controlled clinical trials and are considered to be the fairest method to test whether or not a treatment is effective. We did not examine other types of studies.

What we found

We found seven studies that randomly allocated a total of 225 participants to cognitive training or to a control group. Treatment lasted from four to eight weeks. All the cognitive training interventions were delivered by computer. The control groups received either no intervention or a control intervention such as language or motor exercises or participation in recreational activities. We found no difference between people who received cognitive training and people in the control groups in global cognition shortly after treatment ended. There was no convincing evidence of benefit in specific cognitive skills and no benefit shown in activities of daily living or quality of life. However, these findings were based on a small number of participants in a small number of studies. The overall certainty of the evidence was low, meaning that the results of further research could differ from the results of this review.

Conclusion

We found no good evidence that cognitive training is helpful for people with Parkinson’s disease and dementia or MCI. The included studies were small and had flaws that may have affected the findings. The certainty of the results was low, and further studies are needed before we can be confident whether or not cognitive training is effective for this group of people.

Authors’ conclusions

Implications for practice

Given that many people with Parkinson’s disease (PD) experience cognitive difficulties, the potential benefit of use of cognitive training interventions is large. It will be important that large‐scale trials of effectiveness are conducted, especially in people with PD dementia (PDD). Evidence from this review suggests that cognitive training interventions are generally associated with high levels of adherence. Given the small evidence base, risk of bias, and overall low certainty of the evidence, implications for clinical practice cannot be identified without further research.

Implications for research

Interventions that aim to improve cognition for people with PDD and PD‐related mild cognitive impairment (PD‐MCI) are becoming increasingly important as pharmacological treatment for cognitive symptoms is limited. Our review highlights the paucity of research in the area and that further research is necessary in order to establish whether cognitive training interventions in people with PDD and PD‐MCI may be beneficial. It is important that these trials follow the CONSORT statement. We await evidence from several ongoing trials evaluating the effectiveness of cognitive training in people with PD‐MCI.Despite some progress in definitions of cognition‐based interventions, there is still confusion with regard to how these interventions are defined and described. Our review suggests overall that although most studies provide enough information to be able to separate interventions, treatment protocols are not provided, and often different approaches are grouped under the same definition. It will be important for future research to concentrate on large‐scale trials of clinical effectiveness versus a control comparison intervention, as many studies had to be excluded because the comparison group was another intervention. Updates of this review could additionally examine effectiveness of cognitive training against other active interventions.Future studies should define cognitive impairment and specify type of diagnosis. Most studies to date exclude ‘people with severe cognitive impairment’, so it is likely that in some studies people with mild dementia or MCI were included. It will be important for future research to address this limitation and describe samples in greater detail reporting diagnostic criteria. Future studies should also try to address variation in training period, tasks used (i.e. cognitive only, cognitive and motor tasks), and sensitivity to change of outcome measures.

It will be important to examine whether any effects observed are generalised to everyday function and tasks of daily living. In the current review we are unable to draw any conclusions as to whether cognitive training is associated with improvements in daily life due to the small number of included studies. Future studies should test whether type of intervention evaluated influences efficacy, and comparisons between multicomponent cognitive training interventions, incorporating additional elements such as transfer training and physical training, versus cognitive training alone.

It has been argued that cognitive training may activate mechanisms of cerebral plasticity and slow PD‐associated cognitive decline (Boller 2004). Future studies should investigate the potential mechanisms through which cognitive training may mediate effects on cognition using structural and functional imaging methods, and the extent to which these interventions may slow the progression of cognitive decline (Boller 2004). Research in the area should also address heterogeneity in outcomes, which may hinder future meta‐analyses. In conclusion, our review suggests that there is an urgent need for further large‐scale studies of cognitive training for people with PDD and PD‐MCI.

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Cognitive training interventions for dementia and mild cognitive impairment in Parkinson’s disease

Abstract

Plain language summary

Cognitive training interventions for dementia and mild cognitive impairment in Parkinson’s disease

Authors’ conclusions

Implications for practice

Implications for research

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