Altered executive function in the welders: A functional magnetic resonance imaging study

Manganese exposure and working memory-related brain activity in smallholder farmworkers in Costa Rica: Results from a pilot study

“…Our findings are not consistent with previous functional neuroimaging studies of welders that found associations of elevated Mn exposure with altered brain activation in the prefrontal cortex (Chang et al, 2010;Seo et al, 2016). A study in Korea found that Mnexposed welders (n = 23) with similar accuracy in their performance on a verbal working memory task as the unexposed workers (n = 21) had significantly greater activity in the prefrontal cortex and a more widespread pattern of activity across the brain (Chang et al, 2010).…”

“…A study in Korea found that Mnexposed welders (n = 23) with similar accuracy in their performance on a verbal working memory task as the unexposed workers (n = 21) had significantly greater activity in the prefrontal cortex and a more widespread pattern of activity across the brain (Chang et al, 2010). In contrast, another study in Korea found that Mn-exposed welders (n = 53) performed worse on an executive function test and had less activation of the bilateral superior frontal cortex (part of the prefrontal cortex) compared to unexposed workers (n = 44) (Seo et al, 2016). In these studies, both increased and decreased activation of the prefrontal cortex are suggestive of neural dysfunction, and the distinction may depend on cognitive demand (Seo et al, 2016;Tomasi et al, 2007).…”

“…Toenail and hair Mn concentrations were strongly right-skewed, with few farmworkers having higher concentrations, so we log 2transformed them to improve the linear fit of the model. Covariates associated with Mn exposure and cognition in previous studies [i.e., age at testing and education level (≤6th grade vs. 7-11th grade)] (Damalas and Koutroubas, 2017;de Azeredo Passos et al, 2015;Oulhote et al, 2014;Reuter-Lorenz and Cappell, 2008), including previous fMRI studies (Chang et al, 2010;Seo et al, 2016), were included in the models a priori.…”

“…1). The dorsolateral prefrontal cortex is a region known to be involved in working memory based on previous fNIRS and fMRI studies of healthy adults (Rypma and D'Esposito, 1999;Sato et al, 2013) and it is also known to be affected by Mn exposure (Chang et al, 2010;Seo et al, 2016).…”

“…A recent fNIRS case study of a 55-year-old man in Singapore, who was likely occupationally exposed to Mn at previous workplaces, had elevated urinary concentrations of Mn and decreased activation of the frontal lobe during a verbal fluency test compared to a healthy comparison subject (Ho et al, 2018). In addition, one fMRI study found increased brain activity of the prefrontal cortex during a verbal working memory task (Chang et al, 2010), while another found decreased brain activity in the same region during an executive function task (Seo et al, 2016) in Mnexposed welders compared to un-exposed controls in Korea.…”