Objective Although Manganese (Mn) is essential for brain metabolism, excessive exposure to Mn in occupational settings such as in welding can lead to cognitive and motor deficits. To further study the relation between exposure, brain function and brain Mn accumulation, we developed a new 3D whole-brain MRI approach to visualise the distribution of excessive brain Mn in welders.

Methods We used a voxel-by-voxel analysis of whole-brain R1 relaxation rate mapping as an indicator of Mn deposition in deep brain structures and the cerebral cortex in 30 welders (mean air Mn = 0.18 ± 0.16 mg/m³) and 20 non-exposed controls from the same factory.

Results A wide-spread accumulation of Mn throughout the brain was discerned in our study. Outside the basal ganglia, significantly higher R1 values, indicative of higher Mn concentration, were found in the inferior parietal cortex and insula in welders (all p < 0.005), consistent with deficits in motor control and emotional instability found in Mn-exposed welders. Mn deposition in the supplementary motor cortex, primary motor cortex and somatosensory cortex point toward an effect on the motor regulation network. Elevated Mn concentrations (p < 0.005) were also found in superior primary visual cortex, secondary visual cortex and inferior temporal lobe, all belonging to visual association areas. An especially significant difference was found in the precuneus (p < 0.005), an area engaged in visuospatial function. Whole-brain voxel-by-voxel correlation maps (p < 0.005) show that R1 in motor cortex and basal ganglia correlates with Mn exposure over the past 3 months prior to the MRI scan.

Conclusions These findings suggest that Mn exposure leads to increased Mn accumulation in the motor and visuospatial networks, which may be related to reported impaired neurobehavioral effects.