Cognition‐based interventions for older people and people with mild cognitive impairment
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To evaluate the effectiveness of cognition‐based interventions in healthy older adults and older adults with mild cognitive impairment. This review should help practitioners choose suitable intervention methods, as well as informing future research.
Background
This review will evaluate the effectiveness of cognition‐based interventions in healthy older adults and older adults who have some form of cognitive impairment, but who do not meet diagnostic criteria for dementia.
As our societies age, and at the same time become more technologically complex, there is increasing interest in understanding the effects of ageing on cognitive function (the range of abilities in areas such as attention, perception, memory, and language that we draw on for many activities in our daily lives). Most people, although not all, experience a cognitive decline in old age. There is, however, also evidence for potential gains in performance, in particular in domains where performance is supported by greater experience. This can be demonstrated in a number of areas of expertise, ranging from vocabulary to job‐specific skills and knowledge. These findings show that there is potential for cognitive plasticity (change and adaptation) in later life (Hoyer 2006; Kliegl 1989; Verhaeghen 1992), whereby performance can be enhanced under optimal conditions (Singer 2003). The possible extent and limits of cognitive plasticity in later life remain to be determined.
Understanding more about the processes underlying these changes in cognitive performance may offer various avenues for supporting cognitive functioning in later life. Findings from a number of studies have indicated that cognitively‐stimulating activity may help to protect against cognitive decline in later life (Wilson 2002). Building on these observations, researchers have attempted to enhance or maintain cognitive functioning in older people by means of systematic cognition‐based interventions such as memory training. It is important to establish to what extent cognitive performance can be improved through systematic training across adulthood and old age, and for how long any gains are maintained. It is also important to establish what factors influence the extent of any gains for a given individual, and to determine how different features of the training, such as intensity, frequency, duration, or focus, have on the size of the gains (Hoyer 2006; Nyberg 2005; Willis 2001).
For the majority of older people the extent of any cognitive decline is relatively small, but some individuals develop more extensive difficulties and are at greater risk of developing a form of dementia.
Various terms and definitions have been applied to this group; currently, they are likely to be described as experiencing 'mild cognitive impairment'. Individuals with MCI display subtle cognitive changes that are not severe enough to fulfil diagnostic criteria for dementia, but are greater than those typically observed in their age group (Larrieu 2002; Petersen 2001). Earlier definitions emphasize the differentiation from optimal ageing (e.g. "Benign Senescent Forgetfulness"; Kral 1962; "Age‐Associated Memory Impairment"; AAMI; Crook 1986), or the identification of preclinical dementia patients (e.g. "Malignant Senescent Forgetfulness"; Kral 1962; "Cognitive Impairment, No Dementia"; CIND; Graham 1997). The term MCI as defined by the American Psychiatric Association (APA 1987) is a condition involving impaired short‐ and long‐term memory, but no functional impairment. MCI is assumed to be a precursor of dementia, i.e. a transitional state between normal cognitive decline in old age and dementia. Due to the variability in definitions, studies investigating prevalence and incidence of MCI come to different conclusions (Kratz 2002). Prevalence rates vary between 5% and 25% (Kumar 2005; Manly 2005; Purser 2005), incidence rates between 0.5 and 8% (Busse 2003; Larrieu 2002; Jungwirth 2005).
Older people with MCI constitute a particularly vulnerable, at‐risk group. Cognition‐based interventions may offer the possibility of maintaining or improving cognitive function, and perhaps prevent or delay progression to dementia (Hultsch 1999; Schooler 2001; Stern 2002). It is also important to determine whether the possible benefits differ from those seen in healthy older people, and whether the same or different forms of intervention are most suitable (Nyberg 2005).
Intervention
This review will assess the effectiveness of cognitive training. Cognitive training is defined as an intervention providing structured practice on tasks relevant to aspects of cognitive functioning, such as memory, attention, language or executive function. Standardized tasks are used (Clare 2003) but level of difficulty may be graded to allow for individual variations in ability. The selected tasks vary in degree of specificity, with some interventions focusing on very specific abilities and strategies, and others taking a more multimodal and holistic approach. Cognitive training may be offered in various forms, including individual or group sessions, and tasks may be presented in various modalities, including pencil‐and‐paper or computerised versions. There is wide variation in frequency and duration of training sessions. This intervention approach is intended to address cognitive function and/or cognitive impairment directly and to produce improvements in performance on standardised measures of the relevant domains. Effects on performance of specific tasks trained in the intervention may also be considered.
Rationale
Numerous studies report the effects of cognition‐focused interventions with older people. There is some evidence for cognitive plasticity in later life as well as a possible protective effect of engaging in cognitively‐stimulating activity. This suggests there may be potential to improve cognitive functioning in later life through cognitive training interventions, and this in turn might help to support continued independence and maximise quality of life for otherwise healthy older people. For older people who are already experiencing mild cognitive impairment, and who are at increased risk of developing dementia, cognition‐focused interventions may help to improve or maintain the level of cognitive performance and thereby delay or prevent further decline (Hoyer 2006; Wilson 2002).
The most frequently reported form of cognition‐focused intervention is cognitive training. Cognitive training involves individual or group sessions with practice on tasks targeting aspects of cognitive functioning such as memory, attention and language. The precise parameters of cognitive training interventions reported in the literature vary considerably, and as a result it has been difficult to draw firm conclusions about efficacy. This review aims to gain a clearer picture of the effectiveness of cognitive training, in order to provide guidance on when to apply which training to whom and how often in order to achieve the greatest benefits. Effectiveness can be considered in terms of improvements on test scores in the areas of cognitive functioning targeted in the training, maintenance of improvements over time, transfer of training effects to other kinds of cognitive tasks, and generalisation of effects to everyday functioning. It is also important to consider what factors may be responsible for any benefits resulting from cognitive training, and whether the same, or different approaches are needed for healthy older people and older people with mild cognitive impairment.
Objectives
To evaluate the effectiveness of cognition‐based interventions in healthy older adults and older adults with mild cognitive impairment. This review should help practitioners choose suitable intervention methods, as well as informing future research.
Methods
Criteria for considering studies for this review
Types of studies
Randomized controlled trials, for which adequate information was provided or could be obtained from the researchers.
Types of participants
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Participants aged 65 years or older.
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Any setting
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Either healthy older people with no diagnosis, or older people who meet criteria for mild cognitive impairment
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Participants with a diagnosis of dementia will be excluded
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Profiles of general cognitive ability and cognitive functioning in relevant domains, as indicated by performance on standardised measures, must be documented to allow an evaluation of participants' cognitive status and, specifically, whether they fit the definition of mild cognitive impairment. In order not to exclude studies that may be relevant for this review, none of the specific definitions of mild cognitive impairment are particularly included or excluded, but information on participants' cognitive ability is required for classification of individual cognitive status.
Types of interventions
Studies will be considered for this review if they describe cognitive training interventions targeting specific domains of cognitive functioning such as memory, attention or language. These may be compared with no training, with control conditions comprising a non‐specific, placebo therapy, such as art discussion (Best 1992), or with training targeted at other specific domains (for example, memory training compared with attention training; Scogin 1992). Interventions may be offered in either one‐to‐one or group modalities, and may be presented in a range of formats including paper‐and‐pencil tasks and computerised training programs. Duration of intervention may be up to one year, with at least a baseline and a post‐intervention assessment reported.
Types of outcome measures
Change following intervention in:
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Measures of cognitive functioning, including memory (e.g., Rivermead Behavioural Memory Test, Memory Functioning Questionnaire, name recall, word list recall), language (e.g., verbal comprehension, reading), attention (e.g., verbal series attention test, visual detection) and executive functioning (e.g., Trail Making Test);
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Measures of specific training effects as well as transfer and generalisability;
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Non‐cognitive outcomes including well‐being, quality of life and everyday functioning;
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Follow up data up to one year to assess maintenance of gains;
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For the MCI group, rates of conversion to dementia and, if applicable, rates of institutionalisation as well as impact on carers;
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Incidence and severity of adverse effects.
Search methods for identification of studies
The CDCIG Specialized Register will be searched for randomized controlled trials of the effects of cognition‐based intervention, compared to another intervention, a placebo intervention, or no intervention, in either healthy older people or people with mild cognitive impairment.
The CDCIG Specialised Register contains trial records from health care databases like MEDLINE, EMBASE, CINAHL, PsycINFO as well as ongoing trial records from databases like clinicaltrials.gov, National Research Register and the IPFMA register and is updated regularly. As this Register only covers trials in the field of dementia and cognitive impairment, MEDLINE, EMBASE, CINAHL and PsycINFO will be searched separately to find trials with healthy people.
The search terms used will be 'cognitive stimulation', 'cognitive rehabilitation', 'cognitive training', 'cognitive retraining', 'cognitive support', 'memory function', 'memory rehabilitation', 'memory therapy', 'memory aid*', 'memory group*', 'memory training', 'memory retraining', 'memory support', 'memory stimulation', 'memory strategy', 'memory management'.
Data collection and analysis
Searches will be conducted as detailed above to identify all relevant published studies, and hard copies of articles will be obtained. RCTs will be identified and three reviewers (MM, MA and LC) will work independently to determine which studies meet the criteria for inclusion before reaching a final consensus on which studies to include. Additional information will be sought from study authors as appropriate.
Two reviewers (MM and MA) will independently review all the trials for inclusion in the review.
Quality assessment
The reviewers will assess the methodological quality of randomization in each trial using one of the approaches described in the Cochrane Reviewers' Handbook (Higgins 2008):
In category A (adequate), the report describes allocation of treatment by: (i) some form of centralized randomized scheme, such as having to provide details of an enrolled participant to an office by telephone to receive the treatment group allocation; (ii) some form of randomization scheme controlled by a pharmacy; (iii) numbered or coded containers, as in a pharmaceutical trial in which capsules from identical‐looking numbered bottles are administrated sequentially to enrolled participants; (iv) an on‐site or coded computer system, provided that the allocations were in a locked, unreadable file that could be accessed only after inputting the characteristics of an enrolled participants; or (v) if assignment envelopes were used, the report should at least specify that they were sequentially numbered, sealed, and opaque; (vi) other combinations of described elements of the process that provide assurance of adequate concealment.
Category B (intermediate) is where the report describes allocation of treatment by: (i) use of a ''list'' of ''table'' to allocate assignments; (ii) use of ''envelopes'' or ''sealed envelopes''; (iii) stating the study as ''randomized'' without further detail.
Category C (inadequate) is where the report describes allocation of treatment by: (i) alternation; (ii) reference to case record numbers, dates of birth, day of week, or any such approach; (iii) any allocation procedure that is transparent before assignment, such as an open list of random numbers or assignments. Empirical research has shown that lack of adequate allocation concealment is associated with bias. Trials with unclear concealment measures have been shown liable to yield more pronounced estimates of treatment effects than trials that have adequate measure to conceal allocation schedules, but the effect is less pronounced than inadequately concealed trials (Chalmers 1983; Schulz 1995). Trials were considered if they conformed to categories A or B, but those falling in category C were excluded. Other aspects of trial quality were not assessed by a scoring system but details of blinding, appropriateness of methods and the number of patients lost to follow‐up were noted.
Data extraction
Data from the RCTs selected for inclusion will be extracted by MM and MA. The summary statistics required for each trial and each outcome for continuous data are the mean change from baseline, the standard error of the mean change, and the number of patients for each treatment group at each assessment. Where changes from baseline are not reported, the mean, standard deviation and the number of people in each treatment group at each time point will be extracted if available.
For binary data the number in each treatment group and the numbers experiencing the outcome of interest will be sought.
The baseline assessment is defined as the latest available assessment prior to randomization, but no longer than two months before.
For each outcome measure, data will be sought on every person assessed. It is unlikely that intention‐to‐treat data will be available in the publications, so in general the data of those who complete the trial will be sought and indicated as such. However, in order to allow an intention‐to‐treat analysis, wherever possible the data will be sought irrespective of compliance, whether or not the person was subsequently deemed ineligible, or otherwise excluded from treatment or follow‐up.
Data analysis
The outcomes measured may arise from ordinal rating scales. Where the rating scales used in the trials have a reasonably large number of categories (more than 10) the data will be treated as continuous outcomes arising from a normal distribution.
Summary statistics (n, mean and standard deviation) are required for each rating scale at each assessment time for each treatment group in each trial for change from baseline. For cross‐over trials only the data from the first treatment period will be used.
When change from baseline results are not reported, the required summary statistics will be calculated from the baseline and assessment time treatment group means and standard deviations. In this case a zero correlation between the measurements at baseline and assessment time will be assumed. This method overestimates the standard deviation of the change from baseline, but this conservative approach is considered to be preferable in a meta‐analysis.
Meta‐analysis requires the combination of data from trials that may not use the same rating scale to assess an outcome. The measure of the treatment difference for any outcome is the weighted mean difference when the pooled trials use the same rating scale or test, and the standardized mean difference, which is the absolute mean difference divided by the pooled standard deviation when they used different rating scales or tests.
The duration of the trials may vary considerably. If the range is considered too great to combine all trials into one meta‐analysis the data will be divided into smaller time periods and a separate meta‐analysis conducted for each period. Some trials may contribute data to more than one time period if multiple assessments have been made.
For binary outcomes, such as improvement or no improvement, the odds ratio is used to measure treatment effect. A weighted estimate of the typical treatment effect across trials is calculated.
Overall estimates of the treatment difference will be presented. In all cases the overall estimate from a fixed‐effects model will be presented and a test for heterogeneity using a standard chi‐square statistic will be performed. If, however, there is evidence of heterogeneity of the treatment effect between trials then either only homogeneous results will be pooled, or a random‐effects model used (in which case the confidence intervals would be broader than those of a fixed‐effects model).
