Association of MRI T1 relaxation time with neuropsychological test performance in manganese- exposed welders

•Manganese exposed welders were studied using MRI and neuropsychological testing.•In welders, a shortened MRI T1 relaxation time was found in multiple brain regions.•Welders scored worse on tests of verbal fluency and graphomotor tremor.•Lower neuropsychological test performance was associated with shorter T1 times.•Verbal dysfunction may be an early effect of brain Mn deposition in welders. This study examines the results of neuropsychological testing of 26 active welders and 17 similar controls and their relationship to welders’ shortened MRI T1 relaxation time, indicative of increased brain manganese (Mn) accumulation. Welders were exposed to Mn for an average duration of 12.25 years to average levels of Mn in air of 0.11±0.05mg/m3. Welders scored significantly worse than controls on Fruit Naming and the Parallel Lines test of graphomotor tremor. Welders had shorter MRI T1 relaxation times than controls in the globus pallidus, substantia nigra, caudate nucleus, and the anterior prefrontal lobe. 63% of the variation in MRI T1 relaxation times was accounted for by exposure group. In welders, lower relaxation times in the caudate nucleus and substantia nigra were associated with lower neuropsychological test performance on tests of verbal fluency (Fruit Naming), verbal learning, memory, and perseveration (WHO-UCLA AVLT). Results indicate that verbal function may be one of the first cognitive domains affected by brain Mn deposition in welders as reflected by MRI T1 relaxation times.