The present findings are similar to the results of a previous report in patients with Parkinson’s disease. In that study, a single dose of MPH improved gait speed, decreased TUG times, and reduced stride time variability18
, effects that were also seen in the present study. In that study, MPH also improved EF, but did not affect memory or finger tapping performance; effects that were also very similar to those seen in the present study. The present study extends those previous findings in two critical ways: 1) the MPH effect is shown in generally healthy older adults, and 2) the MPH effect is demonstrated in a placebo-controlled trial. MPH significantly improved TUG times, stride time variability, and EF (e.g., Go-NoGo accuracy), effects that were not seen after treatment with the placebo.
The observed findings could be interpreted in several ways. One interpretation is that cognitive therapy helps to improve mobility in the elderly. This explanation is consistent with the recent reports that have found that older adults who perform better on tests of EF tend to have better mobility and lower fall rates and the idea that mobility in older adults relies upon cognitive function6–12
. This intriguing possibility would suggest that MPH and perhaps other cognition-enhancing therapies may have a role in reducing fall risk among older adults who are likely to suffer from age-associated declines in EF4
. Support for this explanation comes from the specific effects of MPH on TUG, stride time variability and Go-NoGo accuracy (recall and ).
Another explanation of the observed results is that MPH elicited an amphetamine-like effect that improved performance. Similarly, MPH also has known effects on dopamine uptake35
, a neurotransmitter that plays a key role in motor function. One could argue, therefore, that the observed MPH effects are not due to its modulation of cognitive function, but arise from a more direct influence on motor function or the result of the stimulant effects. These possibilities cannot be completely ruled out; however, examination of and suggest that these are not the most likely explanation. Compared to baseline values, gait speed increased similarly in response to MPH and in response to the placebo. Gait speed is a measure that is likely to be especially sensitive to dopamine uptake and stimulant effects, and perhaps also to the expectations of the participants. One could argue that the placebo and MPH evoked similar stimulant effects while the changes in EF, TUG and stride time variability in response to MPH were in fact a specific, cognitive-related response. Compared to steady-state walking, the TUG is a much more complex procedure that includes planning, potentially explaining the difference between its results and those for average gait speed.
Participants in the present study were community-living older adults. Average scores on the MMSE and the Clock Drawing test are consistent with an absence of dementia and only mild or no cognitive decline. Scores on the GDS indicate none-to-mild depressive symptoms, except for the two participants who had more severe complaints about mood, and scores on the Barthel ADL Index and the Frenchay Activities Index indicate that subjects were free of major deficits, consistent with the low (good) scores on the comorbidity index. Nonetheless, self-confidence regarding balance tended to be slightly below normal29
and all subjects complained about their memory. Among older adults, complaints about memory are associated with a wide array of mental health and physical disturbances, including impaired EF, depression and frailty36,37
. Memory, EF, TUG times, average gait speed, and stride time variability were normal or slightly worse than that seen in “healthy” older adults15,17,30,36
. Thus, the participants can be described as generally healthy, functionally independent community-living older adults with normal to mild decline in cognitive function and mobility.
This study has a number of limitations. For example, the sample size and the specific subject characteristics raise questions regarding the generalizability of the findings. Although the mobility outcomes measured have been associated with fall risk, we did not evaluate whether chronic administration of MPH succeeds in lowering fall rates, whether potential benefits outweigh possible risks, or whether the administered dose is optimal. Further investigations are needed to address these issues and to assess more fully the effects of long-term MPH administration and other cognitive-enhancing drugs or therapeutic options on gait, cognitive function, fall risk and their interplay among different older adult populations. Adverse events were not observed in the present study, consistent with previous reports in older patients18–21
, but issues regarding safe administration of MPH in older adults need to be studied further. Still, the findings of the present investigation suggest that such future studies are warranted, highlight the connection between fall risk and cognitive function, and demonstrate the potential of using pharmacologic agents that augment cognitive function as an alternative, complementary therapy for reducing fall risk in older adults.