Longitudinal evaluation of training-induced neural plasticity

Abstract

Neuroplasticity is reflected in the great capacity of the human brain to adapt quickly and efficiently to a broad variety of environmental factors, and comprises an essential prerequisite for learning. In line with the idea of a plastic human brain, previous neuroimaging studies in the field of motor learning have shown that learning a new skill evokes substantial neuroanatomical and neurofunctional changes. Moreover, there is strong evidence that these motor skill training-induced neuronal adaptations occur across the entire lifespan, from birth to old age. However, the neuronal underpinnings of training-induced adaptations in subjects in the middle adulthood have received little scientific attention. Furthermore, previous studies investigating training-induced neuroplasticity focussed rather on strict training protocols than on physical activities practiced as a leisure activity. By aligning a longitudinal study design with two measurement time-points, the present dissertation thesis aims to explore the dynamic processes of brain anatomy and brain function induced by a highly complex motor training practiced as leisure activity in participants between the age of 40 to 60 years. The investigated motor learning task consisted of golf training practiced as leisure activity. Learning to play golf puts high demands on motor and cognitive abilities and is a physical leisure activity that is not restricted to a certain age group. The first study focussed on anatomical changes induced by the motor-training, whereas the second study focussed on changes of functional neuronal recruitment patterns while mentally performing a golf swing. In order to investigate the neuroanatomical underpinnings of training-induced neuroplasticity in golf novices, the first study used structural magnetic resonance imaging (MRI) and the method of voxel-based morphometry. As a main result, the 40 hours of golf practice, performed as a leisure physical activity with highly individual training protocols, have shown to be associated with gray matter increases in a task-relevant cortical network. These substantial neuroanatomical changes were revealed in regions of the sensorimotor cortex and areas belonging to the dorsal stream. It is suggested that these brain regions play a crucial role during the process of motor learning and the control of visuomotor coordination. The control subjects did not show any gray matter changes in these or in other brain areas. Interestingly, those golf novices who practiced most intensively within the 40-hour period demonstrated the strongest neuroanatomical changes in a critical region of the dorsal information stream. These findings demonstrate that a physical leisure activity induces training-dependent changes in gray matter and let assume that a strict and controlled training protocol is not necessary for training-induced adaptations of gray matter. The second study aimed to investigate changes of neuro-functional recruitment patterns that can be ascribed to the golf training, by using the method of functional MRI (fMRI) and a motor imagery task. The analyses revealed increased hemodynamic responses during the mental rehearsal of a golf swing in non-primary cortical motor areas, sub-cortical motor areas and parietal regions in the novice golfers and the control subjects. This result complements previous mental imagery research showing the involvement of motor areas while mentally rehearsing a complex movement, especially in subjects with low skill level. More importantly, only the golf novice group showed changes between the two measurement time-points. Hemodynamic responses were decreased in non-primary motor areas after the 40 hours golf practice interval. Thus, the results indicate that in the barely studied population of middle-aged adults, a complex physical leisure activity induces functional neuroplasticity. This finding supports the idea that an improvement of skill level is associated with a more efficiently working neuronal network.