Seasonal Changes in Microbial Dissolved Organic Sulfur Transformations in Coastal Waters.

The marine trace gas dimethylsulfide (DMS) is the single most important biogenic source of atmospheric sulfur, accounting for up to 80% of global biogenic sulfur emissions. Approximately 300 million tons of DMS are produced annually, but the majority is degraded by microbes in seawater. The DMS precursor dimethylsulfoniopropionate (DMSP) and oxidation product dimethylsulphoxide (DMSO) are also important organic sulfur reservoirs. However, the marine sinks of dissolved DMSO remain unknown. We used a novel combination of stable and radiotracers to determine seasonal changes in multiple dissolved organic sulfur transformation rates to ascertain whether microbial uptake of dissolved DMSO was a significant loss pathway. Surface concentrations of DMS ranged from 0.5 to 17.0 nM with biological consumption rates between 2.4 and 40.8 nM·d-1. DMS produced from the reduction of DMSO was not a significant process. Surface concentrations of total DMSO ranged from 2.3 to 102 nM with biological consumption of dissolved DMSO between 2.9 and 111 nM·d-1. Comparisons between 14C2-DMSO assimilation and dissimilation rates suggest that the majority of dissolved DMSO was respired (>94%). Radiotracer microbial consumption rates suggest that dissimilation of dissolved DMSO to CO2 can be a significant loss pathway in coastal waters, illustrating the significance of bacteria in controlling organic sulfur seawater concentrations.

Developmental profile of slow hand movement oscillation coupling in humans.

In adults, slow hand and finger movements are characterized by 6- to 12-Hz discontinuities visible in the raw records and spectra of motion signals such as acceleration. This pulsitile behavior is correlated with motor unit synchronization at 6-12 Hz as shown by significant coherence at these frequencies between pairs of motor units and between the motor units and the acceleration recorded from the limb part controlled by the muscle, suggesting that it has a central origin. In this study, we examined the correlation between this 6- to 12-Hz pulsatile behavior and muscle activity as a function of childhood development. Sixty-eight participants (ages 4-25 yr) performed static wrist extensions against gravity or slow wrist extension and flexion movements while extensor carpi radialis muscle electromyographic (EMG) and wrist acceleration signals were simultaneously recorded. Coherence between EMG and acceleration within the 6- to 12-Hz frequency band was used as an index of the strength of the relation between central drive and the motor output. The main findings of the study are 1) EMG-acceleration coherence increased with increases in age, with the age differences being greater under movement conditions and the difference between conditions increasing with age; 2) the EMG signal showed increases in normalized power with increases in age under both conditions; and 3) coherence under movement conditions was moderately positively correlated with manual dexterity. These findings indicate that the strength of the 6- to 12-Hz central oscillatory drive to the motor output increases through childhood development and may contribute to age-related improvements in motor skills.

On the development of human corticospinal oscillations: age-related changes in EEG-EMG coherence and cumulant.

Changes in coherence and cumulant calculated between electroencephalograph (EEG) recorded from the scalp over primary motor cortex and rectified surface electromyograph (EMG) recorded from the contralateral wrist extensor muscles have been studied during development in humans (48 subjects, age 0-59 years). Using the techniques of EEG-EMG coherence and cumulant analysis and pooled coherence and cumulant analysis we demonstrate that between childhood, adolescence and adulthood there are increases in the prevalence and magnitude of coherence at frequencies between 15 and 35 Hz with corresponding development of a tri-phasic feature in the EEG-EMG cumulant. The results show for the first time that changes in the cortical approximately 20 Hz oscillatory drive to human motoneurone pools take place during motor development.

Changes in EMG coherence between long and short thumb abductor muscles during human development.

In adults, motoneurone pools of synergistic muscles that act around a common joint share a common presynaptic drive. Common drive can be revealed by both time domain and frequency domain analysis of EMG signals. Analysis in the frequency domain reveals significant coherence in the range 1-45 Hz, with maximal coherence in low (1-12 Hz) and high (16-32 Hz) ranges. The high-frequency range depends on cortical drive to motoneurones and is coherent with cortical oscillations at approximately 20 Hz frequencies. It is of interest to know whether oscillatory drive to human motoneurone pools changes with development. In the present study we examined age-related changes in coherence between rectified surface EMG signals recorded from the short and long thumb abductor muscles during steady isometric contraction obtained while subjects abducted the thumb against a manipulandum. We analysed EMG data from 36 subjects aged between 4 and 14 years, and 11 adult subjects aged between 22 and 59 years. Using the techniques of pooled coherence analysis and the chi(2) difference of coherence test we demonstrate that between the ages of 7 and 9 years, and 12 and 14 years, there are marked increases in the prevalence and magnitude of coherence at frequencies between 11 and 45 Hz. The data from subjects aged 12-14 years were similar to those obtained from adult controls. The most significant differences between younger children and the older age groups were detected at frequencies close to 20 Hz. We believe that these are the first reported results demonstrating significant late maturational changes in the approximately 20 Hz common oscillatory drive to human motoneurone pools.

Cutaneomuscular reflexes following stroke: a 2-year longitudinal study.

Cutaneomuscular reflex responses (CMRs) have been studied in nine stroke patients (55-84 years) starting from the first 1-7 weeks after stroke and continuing at intervals of 6-8 weeks for up to 2 years. Multi-unit surface EMG signals were recorded from the stroke and non-stroke first dorsal interosseous (1DI) hand muscle while subjects gripped a dowel, and concomitant stimulation of the digital nerves of the index finger was delivered at 2.5 x threshold for perception. Motor function was measured using the Motor Assessment Scale (MAS) and patients were classified as having a good or a poor recovery according to their final functional outcome. None of the patients showed a change in the sizes of the E1, I1 and E2 reflex components over time. At initial testing, the size of the E1 component for all patients who showed good recovery fell within the 95% reference range (0-16.5% modulation of background EMG) found for normal age matched controls. In contrast, when first tested, 5/5 patients who showed no significant recovery over the 2-year period, had exaggerated spinal E1 components greater than 16.5%. We conclude that exaggerated E1 components could be predictive of a poor functional outcome at 2 years.

Changes in cutaneomuscular reflex responses in relation to normal ageing in man.

Changes in cutaneomuscular reflex responses (CMRs) have been studied in relation to normal ageing in man. Multiunit surface EMG signals were recorded from right and left first dorsal interosseous (1DI) hand muscles from 23 elderly adults (mean age 71.1, range 58-88 years) and 11 young adults (mean age 25.9, range 19-31 years). Subjects (1) performed index finger abduction and (2) gripped a dowel while concomitant stimulation of the digital nerves of the index finger was delivered at x2.5 threshold for perception. The E1 spinally mediated components of the CMRs recorded from 1DI were significantly smaller in the elderly subjects compared with young subjects for both tasks. The I1 and E2 transcortical components did not show a significant change in size with age although the incidence of I1 components was significantly reduced in the elderly subjects.