In an early review paper, Colcombe and Kramer (2003) conducted a meta-analysis of 18 interventional studies, conducted over a 25-year period. Their general conclusion was that fitness training in the elderly increased performance by approximately .5 of a standard deviation across all tasks tested. Maximal effects were found for tasks related to executive functions, (i.e., aspects of higher cognition principally associated with the functions of prefrontal cortex). The next greatest set of effects were found for cognitive functions associated with the transition from effortful learning to automatic processing (i.e. tasks such as driving, that demand concentration and attention during their learning and execution, but which through practice become more automatic). The next greatest effect was on visuo-spatial factors (i.e., factors associated with visualising and interacting with the three-dimensional world). Finally, effects were found on low-level reaction time tasks: generalised increases in the speed of response to stimuli. The authors concluded that neurocognitive benefits of exercise are apparent right across the life span, but the greatest measurable effects of fitness training are more evident in older participants.
Underscoring these conclusions, Eriksen et al (2011) found that in a randomised control trial in 120 older people, that an exercise intervention reversed declines in hippocampal volumes (by c. 1-2 years – i.e. about 2%) using structural MRI, concomitant with improvements in memory function and increases in circulating BDNF. In other words, regular exercise increases the volume of key brain areas concerned with memory.
Experimentally, aerobic fitness has generally been focused upon in a gymnasium setting (usually using treadmills). Thus, activity can be monitored and quantified. Aerobic status is assessed directly through validated measures of cardiorespiratory function, and changes in cardiovascular status can be monitored directly. Additionally, participants can be prescribed a fitness programme extending for verifiable periods of time (say three one-hour sessions per week). This advantage of controlled laboratory trials is also a disadvantage. Participants volunteering for such trials are, by definition, highly-motivated and interested in engaging with the training regime and sustaining it over a sufficiently great period of time that effects on neurocognitive function may become apparent. Field studies of these functions are much less common and generally rely on self-report measures obtained through the use of questionnaires (see, e.g., Giacobbi et al, 2005).
Laboratory-based interventions have another confound. Recent studies have shown that mere exposure, on an intermittent basis, to nature, has a strong, sustained effect on mood. In a clever recent study, Nisbet and Zelenski (2011) examined the effect of people undertaking walks where they are exposed to nature, versus walking in an enclosed environment. Carlton University, Ontario, is subject to extremes of weather. A substantial fraction of the large campus is connected via a system of extended underground tunnels. They investigated (150 participants; 18-48 years) the effect of walking between two locations on the campus: either through an underground tunnel, or overground past an urban space with trees and other features of the natural environment. Participants underestimated dramatically the likely hedonic benefit of undertaking a seventeen-minute walk outdoors versus a walk indoors. They also found that the effect of the walk itself on affect, or mood, was very substantial (an improvement in score of one third), relative to individuals who undertook a walk indoors. Thus, activity in an outdoor setting is an important and positive moderating variable on individual mood, independent of its effects on cognition.
In a final noteworthy paper, Killingsworth and Gilbert (2011), using a smartphone app, analysed repeated point measures of mood (‘experience sampling’) in 2250 people (ages: 18-88 years). ‘Exercising’ was found to be among the top-three highest mood-enhancing activities in this sample.
Conclusion: get out and walk – regularly!