Neuroplastic changes within the brains of manganese-exposed welders: Recruiting additional neural resources for successful motor performance

Background: In a previous study, regional delivery of manganese (Mn)ions within the brain revealed that the metal accumulates in the basal ganglia, where it induces degeneration of the globus pallidus. Degeneration of the basal ganglia impairs motor ability by compromising an important neural circuit involved in the regulation of motor control. Therefore, much research has been devoted to identifying a sensitive and non-invasive imaging marker to evaluate the functional correlates of Mn-related brain dysfunction. Methods: We performed the first-ever sequential finger-tapping functional MRI (fMRI) experiment to investigate the behavioural significance of additionally recruited brain regions in welders with chronic Mn exposure. Results: During the finger tapping task, activation of the bilateral primary sensorimotor cortex (SM1), bilateral supplementary motor area (SMA), bilateral dorsolateral premotor cortex, bilateral superior parietal cortex and ipsilateral dentate nucleus was higher in the welding group (42 welders) than in the control group (26 controls). The pallidal index correlated with the activation observed in the contralateral SM1 for the finger tapping task of the left hand. The fMRI variables correlated with motor behaviour. Grooved Pegboard performances (right hand) correlated with activation, as seen in the ipsilateral and contralateral SMAs obtained during the finger tapping task of the right hand. Conclusion: Our findings suggest that increased brain activation results from the compensational activation of ancillary cortical pathways, which ensures adequate motor function.