13 research outputs found
Mercury and Selenium Balance in Endangered Saimaa Ringed Seal Depend on Age and Sex
The
endangered Saimaa ringed seal (<i>Pusa hispida saimensis</i>) is exposed to relatively high concentrations of mercury (Hg) in
freshwaters poor in selenium (Se), a known antagonist of Hg. The impact
of age and sex on the bioaccumulation of Hg and Se was studied by
analyzing liver, muscle, and hair samples from seals of different
age groups. Adult females were found to accumulate significantly more
Hg in the liver (with ca. 60% as HgSe), and less Hg in the muscles
compared to adult males, which may be explained by accelerated metabolism
during gestation and lactation. In adult seals, molar Se:Hg ratios
in the muscles fall below one, which is considered a threshold for
the emergence of adverse effects. As a result, Saimaa ringed seals
may be at risk of developing health and reproductive problems. According
to mass balance calculations, the pups are exposed to considerable
amounts (μg/d) of mercury during gestation, although lactation
is their main exposure route. In lanugo pups, Hg concentrates in the
hair, and molting serves as a main detoxification route. For other
age groups, demethylation followed by the formation of HgSe is the
main detoxification route, and the demethylation capability develops
in pups by the time of weaning
“Seeing” electroencephalogram through the skull: imaging prefrontal cortex with fast optical signal
Near-infrared spectroscopy is a novel imaging technique potentially sensitive to both brain hemodynamics (slow signal) and neuronal activity (fast optical signal, FOS). The big challenge of measuring FOS noninvasively lies in the presumably low signal-to-noise ratio. Thus, detectability of the FOS has been controversially discussed. We present reliable detection of FOS from 11 individuals concurrently with electroencephalogram (EEG) during a Go-NoGo task. Probes were placed bilaterally over prefrontal cortex. Independent component analysis (ICA) was used for artifact removal. Correlation coefficient in the best correlated FOS–EEG ICA pairs was highly significant (p < 10−8), and event-related optical signal (EROS) was found in all subjects. Several EROS components were similar to the event-related potential (ERP) components. The most robust “optical N200” at t = 225 ms coincided with the N200 ERP; both signals showed significant difference between targets and nontargets, and their timing correlated with subject’s reaction time. Correlation between FOS and EEG even in single trials provides further evidence that at least some FOS components “reflect” electrical brain processes directly. The data provide evidence for the early involvement of prefrontal cortex in rapid object recognition. EROS is highly localized and can provide cost-effective imaging tools for cortical mapping of cognitive processes