Sex differences in surface EMG interference pattern power spectrum.

Sex differences in the spectral parameters of the surface electromyogram (EMG) power spectrum were studied during voluntary muscle contractions of different strength with rest in between. The influence of two different types of leads (unipolar and bipolar) on the values of the spectral parameters was also investigated under the same experimental conditions. The subjects were 15 healthy female and 15 healthy male volunteers. The relationship between the amplitude (root mean square) of the EMG and the force developed was not linear. The mean values of the median power frequency were lower in women than in men. With both types of lead, the increase in force was accompanied by a progressive increase in median power frequency in male and female subjects. The significant differences in spectral parameters observed in the two sexes are probably correlated with anatomic differences.

Quantitative description of EEG periodicities during stationary sleep stages.

A quantitative method was applied in order to assess variations in EEG activities during sleep. Three classes of variations were distinguished: variations connected with sleep-stage changes (class 1), higher-frequency variations described by the envelope of frequency-band activities (class 2), intermediate-frequency variations, corresponding to periods from 4 to 120 s (class 3). For each class, parameters characterizing the frequency spectra were computed. These parameters were mathematically simple and clear in their meaning, since they measured power, modulation index and mean squared frequency. A statistical comparison of the mean values of the parameters during different sleep stages evidenced a certain number of significant shifts in each of the three classes. The most important class-1 and class-2 variations were described by our parameters with high levels of significance. The results obtained for class 3 were in agreement with visual observations reported in the literature, such as the progressive increase in the interval between successive arousals from sleep onset to Stage 4 and the frequent occurrence of cyclic alternating patterns during Stage 2 epochs immediately preceding REM sleep.

A study of the interhemispheric correlation during sleep in elderly subjects.

The interhemispheric relationship during sleep in elderly subjects was studied throughout the night by a minute-by-minute computation of two linear correlation coefficients between right and left EEG activities. One of these coefficients (X delta) related to the 1-4-Hz band activity, and the other (X sigma) to the 12.5-14.5-Hz band activity. For five of the six subjects examined, it was found that the rapid-eye-movement (REM) mean values of both coefficients were significantly different from the nonrapid-eye-movement (NREM) values. A comparison between this elderly group and a control group of young subjects, examined previously, did not reveal any significant shift, either for the REM or for the NREM mean values of the coefficients.

Topographic variations in EEG asymmetry during sleep.

EEG signals were recorded in 11 normal subjects from F4-C4, F3-C3, P4-O2 and P3-O1 during both stage 2 and the REM stage of each NREM/REM cycle. The logarithm of the right/left ratio for the power in the range of the various frequency bands showed a prevalent right-side asymmetry only with the fronto-central derivations. This trend, observed for all frequency bands, remained stable over the various NREM/REM cycles with the exception of the last one. These data indirectly support the hypothesis that the right hemisphere is more heavily involved in dreaming than the left, and suggest a prevalent involvement of the anterior regions.

Changes in the interhemispheric correlation during sleep in normal subjects.

The correlation coefficients between left and right activity in the various frequency bands of the EEG signal were computed during sleep for 11 normal adults. The values of the correlation during REM sleep were compared with those for NREM sleep. This comparison was performed 'locally,' i.e., during each period of the REM-NREM cycle, as well as over the whole night. For 9 out of the 11 examined subjects, both a visual comparison with the hypnogram and a statistical analysis showed the existence of cyclic variations during the night in the delta and/or sigma correlation coefficient. These variations lasted for the whole night and were synchronized with the REM-NREM cycle. A possible connection between these results and data on the interhemispheric relationship given by amplitude analysis is briefly discussed.

A simple method for the quantitative description of sleep microstructure.

A simple method for the quantitative description of sleep microstructure is proposed. This method is based on the computation of descriptors which provide a normalized measure of how the amplitude of the activity in a frequency band differs, at a given instant, from its background. The use of these descriptors makes it possible to identify epochs of transient increase in band activity, to measure their length, and to measure the time distance between two successive epochs.

Differences between surface EMG in male and female subjects evidenced by automatic analysis.

40 healthy volunteers (20 males and 20 females) have been studied by an automatic analysis of their surface EMG. The power density spectrum (PDS) of the electromyographic signal, derived from the tibialis anterior muscle, was used to evaluate the RMS values of the EMG developed during maximal voluntary (Vc) and evoked (Vm) contractions. The ratios between Vc, calculated over each of 5 frequency bands (5-15, 20-40, 45-70, 75-110, 115-160 Hz), and the total Vc have also been calculated. No significant differences emerge in the Vm values for males and females, whereas the Vc values for female subjects are found to be significantly reduced (P less than 0.001) with respect to the corresponding values for males. Significant differences have also been found concerning the percentage distribution of power in the above mentioned frequency bands for men and women (P less than 0.001). It can thus, be hypothesized that there are two different modalities of motor unit recruitment and that different sociological and cultural traditions may be more important in producing these differences than sexually determined physiological differences.

Automatic analysis of surface EMG (preliminary findings in healthy subjects and in patients with neurogenic motor diseases).

Supramaximal electrical stimulation of a motor nerve produces a full contraction of a muscle and the corresponding compound action potential can be recorded. Recent studies appear to support the view that all the motor units are activated during voluntary maximal contraction, at least in the tibialis anterior muscle. The compound action potential and the EMG interference pattern in the tibialis anterior are regarded as two different manifestations of the activation of all the motor units. A method has been developed which compares these EMG activities, by automatic analysis, in order to obtain useful parameters for clinical applications.