Clare and Woods categorized mental stimulation interventions into three types based on the mode of delivery and the goals of the intervention: cognitive stimulation, cognitive rehabilitation and cognitive training.2

Cognitive stimulation refers to the involvement in group activities that are designed to increase cognitive and social functioning in a non-specific manner. Examples of cognitive stimulation activities include participation in group discussions, supervised leisure activities, list memorization with no particular support and also more structured activities such as reminiscence therapy that involves the discussion of past activities, events and experiences.

Cognitive rehabilitation involves individually tailored programmes centred on specific activities of daily life. Examples include learning the name of a new caregiver, balancing a chequebook or improving conversational fluency.2 Cognitive rehabilitation is a more individualized approach to helping people with cognitive impairments in which those affected and their families work together with healthcare professionals to identify personally relevant goals and devise strategies for addressing these. The emphasis of cognitive rehabilitation is not on enhancing performance in cognitive tasks as such, but on improving mental functioning of the patient in realistic situations.

Cognitive training involves teaching theoretically motivated strategies and skills in order to optimize cognition functioning. Cognitive training is most often provided individually or in small groups. Cognitive training typically involves guided practice on a set of standard tasks designed to reflect particular cognitive functions, such as memory, attention or problem solving. The underlying assumption is that practice has the potential to improve or at least maintain functioning in the given cognitive domain. The training is occasionally facilitated by family members with therapist support. Tasks may be presented in paper-and-pencil or computerized form or may involve analogues of activities of daily living. Usually a range of difficulty levels is available within a standardized set of tasks to allow for selection of the level of difficulty that is most appropriate for a given individual. The Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) Study, which randomized 2832 non-demented elderly participants to a 6 week intervention, focused on memory, reasoning and speed of processing, is an example of this form of intervention.3

Support for the potential role of mentally stimulating activities in preventing or mitigating cognitive decline comes from animal studies and also observational studies in humans and, to a lesser extent, randomized clinical trials.

Animal Studies

Exposure to environments enriched with various sensory stimuli and motor demands (enriched environment) is considered the animal equivalent of participation in mentally stimulating leisure activities by humans, although obvious species differences limit direct extrapolation of findings from rodents to humans.4 In the 1960s, Rosenzweig and colleagues reported changes in brain neuroanatomy and neurochemistry in rats exposed to enriched environments, including increased cerebral cortex thickness.5, 6 In the 1970s, Greenough et al. reported finding greater synapse density, glial cell proliferation and structural changes in nerve cells, including increased dendritic branching in rats exposed to enriched environments compared with rats living in standard housing.7 Recent studies have found increases in levels of acetylcholine, a neurotransmitter involved in cognition and in various neurotrophic factors, in rodents exposed to enriched environments.4 Environmentally enriched conditions have been shown to reduce cognitive deficits in young and adult animals.4 Neurogenesis has been demonstrated not only in the adult rodent hippocampus, olfactory bulb and cerebral cortex, but also in primates and humans.4, 8 These findings indicate a substantially important role of the external environment in inducing neurochemical, morphological and behavioural changes in the brain.4, 8

Observational Studies

There is increasing evidence for the role of lifestyle factors as moderators of differences in cognitive ageing and as protective agents for the development of Alzheimer’s disease from observational studies in older adults. Lifestyle factors that have been extensively studied in the context of cognitive decline include education, occupational status and participation in leisure activities. Previous observational studies have found that high levels of participation in mentally stimulating leisure activities decreased the risk of dementia or cognitive decline. For instance, one study found leisure activities such as travelling, doing odd jobs, knitting and gardening to be associated with a reduced risk for dementia. In another study, frequency of participation in common cognitive leisure activities (e.g., reading books; playing games such as cards, checkers/draughts, crosswords or other puzzles; and going to museums) was assessed at baseline for 801 elderly Catholic nuns, priests and brothers without dementia.9 During follow-up, a one-point increase in the cognitive activity score was associated with a 33% reduction in the risk for Alzheimer’s disease. Additionally, engagement in cognitive leisure activities was also associated with slower rates of cognitive decline. In another prospective study, participation in a variety of leisure activities characterized as either intellectual (such as reading, playing games or going to classes) or social (such as visiting friends or relatives, going to movies or restaurants or doing community volunteer work) was assessed in a population study of 1772 non-demented elderly people living in New York city.10 During follow-up, subjects who reported higher levels of participation in these activities at baseline had a 38% less risk of developing dementia.