Effects of occupational exposure to low frequency noise on cognition

Previous studies performed on groups of workers employed in the aeronautical industry revealed morphological vascular changes of the central nervous system (CNS) and some difficulty in attention and memory retention. The goal of this study is, therefore, to determine whether prolonged occupational exposure to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) (LPALF) noise leads to cognitive deterioration.

We observed 40 male workers employed as aircraft technicians, with average age of 43.3 yr (range 35-56, SD = 4.82) occupationally exposed to LPALF noise for a long period of time, average 22 yr (range 13-30, SD = 4.90), and 30 educationally- and age-matched male controls. None of the subjects had a history of alcoholism, and all were drug-free. The P300 event-related brain potential elicited with an auditory discrimination task was recorded and psychological tests (the Wechsler memory scale and the Toulouse-Piéron test) were performed.

The P300 latency was significantly longer (328.5 vs. 307.5 ms, F = 11.7, deg. signif.=0.001) and the amplitude significantly smaller (10.9 vs. 12.6, F = 4.3, deg. signif.=0.04) in the exposed group than in the controls. No significant differences were found in the results of the Toulouse-Piéron test. The different subscales of the Wechsler memory scale did not show any significant difference except in the immediate verbal memory, where the exposed workers were found to have poorer results than the controls (10.0 vs. 11.3, F = 5.6, deg. signif.=0.02). However, the memory quotient obtained from the Wechsler memory scale indicated a significant difference between both groups (101.8 vs. 108.3, F = 10.1, deg. signif.=0.002); exposed subjects presented lower results.

These findings suggest that prolonged exposure to LPALF noise might contribute to cognitive impairment and that the P300 event-related brain potential recording may be a valuable diagnostic tool.