Although an essential nutrient, manganese (Mn) can be toxic at high doses. There is, however, uncertainty regarding the effects of chronic low-level Mn-exposure. This review provides an overview of Mn-related brain and functional changes based on studies of a cohort of asymptomatic welders who had lower Mn-exposure than in most previous work. In welders with low-level Mn-exposure, we found: 1) Mn may accumulate in the brain in a non-linear fashion: MRI R1 (1/T1) signals significantly increased only after a critical level of exposure was reached (e.g., ≥300 welding hours in the past 90 days prior to MRI). Moreover, R1 may be a more sensitive marker to capture short-term dynamic changes in Mn accumulation than the pallidal index [T1-weighted intensity ratio of the globus pallidus vs. frontal white matter], a traditional marker for Mn accumulation; 2) Chronic Mn-exposure may lead to microstructural changes as indicated by lower diffusion tensor fractional anisotropy values in the basal ganglia (BG), especially when welding years exceeded more than 30 years; 3) Mn-related subtle motor dysfunctions can be captured sensitively by synergy metrics (indices for movement stability), whereas traditional fine motor tasks failed to detect any significant differences; and 4) Iron (Fe) also may play a role in welding-related neurotoxicity, especially at low-level Mn-exposure, evidenced by higher R2* values (an estimate for brain Fe accumulation) in the BG. Moreover, higher R2* values were associated with lower phonemic fluency performance. These findings may guide future studies and the development of occupation- and public health-related polices involving Mn-exposure.

锰（Mn）虽然是必需的营养素，但在高剂量下仍可能有毒。但是，关于慢性低水平锰暴露的影响尚不确定。这项综述基于对无症状焊工的锰暴露水平低于以往大多数研究的一组无症状焊工的研究，概述了与锰相关的大脑和功能变化。在低水平锰暴露的焊工中，我们发现：1）锰可能以非线性方式积聚在大脑中：仅在达到临界暴露水平后，MRI R1（1 / T1）信号才会显着增加（例如，在MRI之前的90天内≥300个小时的焊接时间。此外，R1可能是捕捉Mn积累的短期动态变化的敏感标志，而不是传统的Mn积累指标-苍白球指数（苍白球与额叶白质的T1加权强度比）。2）慢性锰暴露可能导致微观结构的变化，这表现为基底神经节（BG）中较低的扩散张量分数各向异性值，特别是当焊接年限超过30年时；尤其是当焊接年限超过30年时；3）通过协同指标（运动稳定性指标）可以敏感地捕获与锰有关的细微运动功能障碍，而传统的精细运动任务无法发现任何显着差异；4）铁（Fe）也可能在焊接相关的神经毒性中发挥作用，尤其是在低水平的Mn暴露中，这由BG中较高的R2 *值（脑铁蓄积的估计值）证明。此外，较高的R2 *值与较低的音素流畅度相关。这些发现可以指导未来的研究以及涉及锰暴露的与职业和公共卫生相关的政策的发展。