Neuron loss and dysfunctionality in hippocampus explain aircraft noise induced working memory impairment: a resting-state fMRI study on military pilots.

Abstract

Long-term aircraft noise exposure may cast a detrimental effect upon the working memory of military pilots, and the brain structural and functional bases of noise related cognitive impairment remains unclear. In this study, we enrolled 30 fighter jet pilots and 30 matched controls. The working memory performance of the subjects was measured with a neurobehavioral test battery including immediate verbal/visual memory and delayed verbal/visual memory tests. Structural MRI and resting-state functional magnetic resonance imaging (rs-fMRI) were utilized to quantify brain grey matter volumes (GMV), regional homogeneity (ReHo), amplitude of low-frequency fluctuation (ALFF) and fractional ALFF (fALFF) differences between the two groups. Furthermore, correlation analyses were performed to find the association between the neural imaging changes with individual neurobehavioral performance. The military pilots showed significantly lower accuracy in delayed verbal and visual memory tests in comparison to the controls, indicating a potential working memory deficit in this population. Structural MRI data and rs-fMRI data showed that the pilots displayed markedly decreased GMVs, ReHo and ALFF signals in the left hippocampus, suggesting neuron dysfunction of the hippocampus. Besides, ReHo and ALFF/fALFF analysis also revealed reduced ReHo in the left amygdala, left thalamus, left superior temporal gyrus and right superior/middle frontal gyrus, indicating disrupted local neural activity under chronic noise exposure. Furthermore, Spearman correlation analysis proved that the GMV and ReHo of left hippocampus were significantly associated with working memory accuracy. This study provided direct evidence of dysfunctional hippocampus serving as the structural and functional bases for neuropsychological impairment under aircraft noise exposure.