The thalamus is a large “chamber” connected to the spinal cord, located in the forebrain. It is connected to the cerebral cortex via nerve fibres facilitating cross-talk. Functions of the thalamus include the regulation of consciousness, sleep, and alertness.
Air pollution is known to have effects on brain volume, however limited information was available regarding the relationship between air pollution and thalamus volume in particular. A study led by Bruce L. Brown of Brigham Young University, Provo, Utah, USA, sought to address this gap in knowledge by investigating the possible association between measures of air pollution and thalamic volume in adults participating in the UK Biobank. The results were published in the journal PLOS One.
Particulate matter (PM) between 2.5 and 10µm (PM2.5-10) was associated with less left but not right thalamic volume. Every one-unit increase in PM2.5–10 was associated with a 0.15% decrease in left thalamic volume. There were no associations between PM2.5, PM10, NO2, and NOX, and thalamic volume.
Age was a factor in thalamic volume and educational achievement appeared protective of thalamic volume against PM2.5, NO2, and NOX. Higher self-rated health also appeared to be protective against PM2.5–10.
The authors note that how the results relate to cognitive or neuropsychiatric phenotypes requires further research. The authors also note that the UK has relatively low levels of air pollution compared to other countries, where the effect on thalamic volume may be more pronounced.
Limitations of the study include that the mechanism by which PM2.5–10 was associated with decreased left thalamic volume was not investigated. The association found in the study does not confirm causation. There may have been a selection bias as only a subset of the UK Biobank has received brain imaging. The possibility of confounding by blood glucose or lipid concentrations exists.
“The results of this study taking into account its limitations suggest a possible association between exposure to air pollution and thalamic volume in adults, with some groups possibly being more susceptible to the effects of air pollution on thalamic volume. Increasing age and comparatively lower education might be risk factors for an effect of air pollution on the thalamus. Given the preliminary nature of these findings, they require verification particularly in samples where mean exposure to air pollution is higher than that in the UK Biobank. The effects of this association also require additional research to determine their effects if any on neurocognitive and neuropsychiatric function,” concluded the authors.