Abstract
The aging brain undergoes remodeling processes because of biological and environmental factors. To counteract brain aging, neuronal plasticity should be preserved. The aim of this study was to test if the capacity of generating short-time synaptic plasticity in older adults may be related to either physical activity, nutritional status, cognition, or neurophysiological activity. Thirty-six participants (mean age 73.3 ± 5.9 years) received transcranial magnetic stimulation in combination with peripheral nerve stimulation to experimentally induce short-time synaptic plasticity by paired associative stimulation (PAS). Adaptations in neuronal excitability were assessed by motor-evoked potential (MEP) in the right m. tibialis anterior before and after PAS. The Physical Activity Questionnaire 50+ and the StepWatchTM captured physical activity levels. Nutritional status was assessed by the Mini Nutritional Assessment. Cognition was assessed by reaction time for a divided attention test and with the Montreal Cognitive Assessment. Neurophysiological activity was assessed by electroencephalography during the divided attention test. MEPs of the highest stimulation intensity resulted significantly different comparing before, 5 min, or 30 min after PAS (p < 0.05). Data-driven automatic hierarchical classification of the individual recruitment curve slopes over the three-time points indicated four different response types, however, response groups did not significantly differ based on physical activity, nutritional status, cognition, or neurophysiological activity. In a second-level analysis, participants having an increased slope showed a significant higher energy expenditure (z = -2.165, p = 0.030, r = 0.36) and revealed a significant higher power activity in the alpha frequency band (z = -2.008, p = 0.046, r = 0.37) at the prefrontal-located EEG electrodes, compared to the participants having a decreased slope. This study hints toward older adults differing in their neuronal excitability which is strongly associated to their short-time synaptic plasticity levels. Furthermore, a physically active lifestyle and higher EEG power in the alpha frequency band seem to be connected to the capacity of generating long-term potentiation-like synaptic plasticity in older adults. Future studies should consider more sensitive assessments and bigger sample sizes to get a broad scope of the older adults’ population.
Highlights
Aging is a naturally occurring physiological process that develops without concurrent diseases (Mora, 2013)
The aim of this study was to test whether the capacity of generating short-time synaptic plasticity in older adults may be related to either physical activity, nutritional status, cognition, or neurophysiological activity
Comparing motor-evoked potential (MEP) peak-to-peak amplitudes over all threetime points, significant differences were found for 130% resting motor threshold (RMT) [χ2(2) = 6.000, p = 0.050, n = 36] and 140% RMT [χ2(2) = 13.556, p = 0.001, n = 36] (Supplementary Table 1)
Summary
Aging is a naturally occurring physiological process that develops without concurrent diseases (Mora, 2013). The central nervous system, in general, is affected by aging- and behavior-related alterations. This alteration process includes changes in brain neurochemistry as well as in neuroanatomical structures including gray and white matter (Park and ReuterLorenz, 2009; Seidler et al, 2010). Atrophy of the motor cortical regions may coincide with motor performance declines such as movement slowing, disorders in balance, and instable gait leading to fall events and fragility that, in turn, affect activity of daily living and maintenance of older adults’ independence (Seidler et al, 2010). Better understanding about brain plasticity might help older adults to counteract weakness, to remain independent and to get a balanced life (Taube et al, 2008)
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