Tremor in Cree subjects exposed to methylmercury: a preliminary study

Rest, postural, and kinetic tremors were recorded in Cree subjects (n = 36) exposed to low levels of methylmercury (MeHg) and control subjects (n = 30) using lasers designed to measure displacement. Displacement and derived velocity and acceleration time series were analyzed using quantitative characteristics in time and frequency domains. We found: 1) relatively low agreement between our results and those of a clinical examination done at the time of testing (r = 0.31 for postural tremor); 2) best discrimination with velocity of static (postural with visual feedback) and kinetic tremors for which significant differences between the two groups are found in many of the characteristics examined; 3) myoclonic-like finger microdisplacements in tremor of Cree subjects; 4) significant changes in static tremor of Cree subjects following a kinetic task; 5) significant differences among three age-matched subgroups of six subjects each (Cree with higher and lower MeHg level, and a control group) in characteristics that reflect difficulty with tracking, myoclonic-like microdisplacements and change in frequency composition of tremor after the tracking task. The subtle differences detected in this preliminary study suggest that further work is warranted to determine whether they can be unambiguously associated with exposure to MeHg.