Plasticity in healthy old age : a multi-domain training approach

Abstract

Aging has an impact on people’s social, cognitive, and physical functioning. Despite great individual variability, healthy aging occurs along with declines in the maximal performance of several cognitive abilities including spatial navigation and memory, visuomotor skills, and executive functions, while other abilities are spared or even improve. An increasing number of older adults fears age-related losses that affect quality of life and independent functioning. Therefore, maintaining cognitive abilities is of interest from both an individual’s perspective and from a societal one since the demographic change leads to the need of keeping older adults in the workplace. Plasticity refers to the malleability of cognitive and neural functioning. This malleability is preserved across the adult lifespan until very old age and is known to be exploited by training. Considerable scientific effort has been put into finding effective interventions to improve and stabilize cognitive and brain functioning during aging. However, evidence for domain-general and long-lasting improvements has been sparse, and the mechanisms of cognitive training are not well understood. The present thesis focuses on multi-domain training, a training approach that combines exercising cognitive, physical, and social abilities. Thus, it has the potential to increase each trained domain as well as the ability to orchestrate multiple domains. First, available multi-domain training studies are reviewed. This literature review concludes that previous multi-domain training approaches have not been significantly informative regarding the impact of a particular type of multi-domain training on transfer. To fill this gap, a novel training tool has been developed. This novel training tool, called “Hotel Plastisse”, is introduced secondly. “Hotel Plastisse” is an iPad-based training specifically designed to compare the simultaneous training of three cognitive functions (multi-domain training) to the training of each single cognitive function (single-domain training). The trained domains are clearly defined and separable from each other. Thereby, training-related improvements can be related to transfer in a theoretically informed way. Furthermore, the training environment is designed as a motivating learning environment in a virtual hotel, incorporating an adaptive difficulty algorithm and providing detailed feedback. These are design aspects that are increasingly recognized as critical in the training literature. Third, a cognitive training study examines near and far transfer of single-domain and multi-domain training. Eighty-four healthy older participants aged 64 to 75 years trained either inhibition, visuomotor function, or spatial navigation (single-domain training groups), or the simultaneous combination of these three functions (multi-domain training group). With respect to near transfer, the single-domain and the multi-domain training groups did not differ. With respect to far transfer, improvements on attentional control were more pronounced in the multi- domain training group than in the single-domain training group. Furthermore, independent of training group, individuals with lower baseline performance showed higher training-related change on the transfer test battery compared to individuals with higher baseline performance. Six months after training, training-related improvements remained stable. The findings show that multi-domain training enhances functions that involve handling several different tasks at the same time, which is an everyday challenge especially for older people. Fourth, functional brain network characteristics are compared between three groups of participants that differed with respect to their training history (multi-domain training group, visuomotor function training group, participants with no training history). One year after training, participants underwent high-density electroencephalographic (EEG) measurement to examine expertise-related functional connectivity and small-world network characteristics during performance on the multi-domain training task. The multi-domain training group performed significantly better than the visuomotor function training group and the control group (no training history). In addition, the multi-domain training group showed enhanced and more efficient functional connectivity in a task-related network encompassing visual, motor, executive, and memory-associated brain areas. Hence, the findings show expertise-dependent differences in performance and neural network characteristics even a year after training. Taken together, the thesis presents evidence for cognitive and neural plasticity in healthy older adults induced by a simultaneous multi-domain training. Training regimes that target older adults’ ability to handle several tasks simultaneously may enhance the probability for an overlap with different situations. Future studies should take methodological approaches that allow researchers to relate inter-individual differences to training progress and transfer. In addition, neuroimaging will lead to a better understanding of the neurobiological bases of plasticity. Well-informed experimental paradigms combined with sophisticated behavioral and neuroimaging data analyses will provide further insights into the mechanisms of training- induced plastic changes in healthy aging, and will thereby advance the development of effective interventions.