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Neural adaptations in response to long-term balance learning in young and old: Behavioral, structural, functional and neurophysiological adaptations

Description: BACKGROUND: Postural control differs between young and elderly and elderly face a higher risk of falls. Thus, balance training is recommended as a countermeasure. However, in addition to deficits in postural control, evidence suggests slower and/or different learning processes in old age. In young subjects, neural plasticity in cortical structures (e.g. M1, SMA) was observed after learning balance tasks for 4 to 6 weeks. Subjects displayed also improved performance not only in the explicitly trained exercises but also in transfer balance tasks. In contrast, neural and behavioral adaptations seem to occur slower and may even involve different brain areas in the elderly. The current study therefore compares long-term learning of balance tasks with respect to behavioural, structural and functional brain adaptations between young and old subjects. Electrophysiological and imaging methods are used to determine adaptations after 2 and 6 months a) at rest (white and grey matter microstructure with quantitative MRI; qMRI), b) during mental simulation of balance tasks (fMRI, TMS) and c) during actual execution of balance tasks (TMS, NIRS). Positive transfer effects on learning and performance of novel postural tasks are tested after the 6 months training. WORKING HYPOTHESIS: The working hypothesis is that both young and elderly will improve performance in the trained exercises after 2 months. However, transfer adaptations in non-trained balance tasks are expected to occur preferentially in young subjects at this stage. After 6 months, we presume to find transfer adaptations also in elderly participants but expect less task automatization (tested with a dual-task). Pronounced cortical adaptations are expected in the frontal cortex in young subjects after 2 months of training followed by more subcortical adaptations after 6 months. For the elderly, we expect a time lag in cortical-to-subcortical progression of training-dependent plasticity and a shift towards youth-like brain activation patterns i.e., reduced over-activation and dis-inhibition. This hypothesis will be tested with fNIRS and TMS to evaluate brain activation during real task execution. In addition, TMS and fMRI will be applied while participants mentally simulate postural tasks. Finally, training-dependent structural plasticity in cortical and subcortical areas will be investigated with a novel MRI technique (qMRI) that enables us to infer myelin- and iron-related microstructural properties of the grey matter. In young subjects, it was previously shown that training-induced increases in prefrontal gray matter were positively correlated with changes in balance performance. Furthermore, TMS-experiments displayed a correlation between changes in excitability in M1 and postural skill acquisition. So far, no studies could show such interrelations in prefrontal and motor cortical areas in the elderly. Therefore, the present study will shed light on the question if elderly adapt slower and/or different (e.g. other brain areas) than young participants. EXPERIMENTAL DESIGN: We will recruit 40 healthy elderly human subjects and 40 healthy young adults. Elderly as well as young adults will be randomly assigned into a training or control group. The two training groups will undergo a 6-months balance training intervention after the pre-test. All subjects will be tested two and six months after the pre-test to assess behavioral, functional and structural brain changes. A behavioral retention test is scheduled 6 months after cessation of the training. METHODS: All test sessions involve the assessment of behavioural parameters like centre of pressure displacement during balancing on solid and moveable ground as well as during balance recovery reactions following perturbation. Importantly, balance skills will be assessed in tasks that are part of the training and in tasks that are not trained. Furthermore, changes in the capability to learn new balance tasks are assessed after the training (learning to learn transfer). The underlying neural adaptations will be investigated with behavioural, electrophysiological (TMS), and imaging techniques (fMRI, qMRI, fNIRS). EXPECTED VALUES OF THE PROPOSED PROJECT: The current project will provide knowledge not only about long-term learning processes of postural control but will also give new insights into age-dependent long-term adaptations of the central nervous system. As long-term learning studies are rare, this knowledge is important to better understand learning in general. Furthermore, the combination of different methodological approaches allows a comprehensive assessment of balance training induced changes in the central nervous system. We combine neural and behavioural measures to better understand the effects of long-term motor learning. For instance, transient structural and functional adaptations may be differentiated from (more) persistent ones and the question can be addressed, whether supraspinal activity indeed shifts from predominantly cortical (prefrontal) to more subcortical centers in both young and elderly subjects. Furthermore, neuroplasticity in elderly subjects can directly be compared to adaptations in young people, offering the possibility to better tailor learning interventions for the elderly.

Funder: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung

Amount: CHF 397,300

Funding type: research

Funder scheme: Project funding

Start date: 2016-04-01

End date: 2019-03-31

Investigator: Taube, Wolfgang

Institution: University of Fribourg – FR

Topic: Balance, Gait, and Falls Prevention

Subfield: Physical Therapy, Sports Therapy and Rehabilitation

Field: Health Professions

Domain: Health Sciences