Interhemispheric differences of hand motor cortex organization: MEG-EMG cortico-muscolar coherence

Corticomuscular coherence between cerebral cortical rhythms and the surface electromyography (EMG) has been observed both trough electrocorticogram and by electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings. Corticomuscular coherence is a tool for identification and characterization of cortical districts controlling a particular body district, based on amplitude and frequency selection. MEG recordings of parietal contralateral cerebral activity and muscular activity from right and left extensor comunis digitorum (ECD) have been studied in 5 control subjects (bandpass 0.48-250 Hz, sampling rate 1000 Hz). Subject was required to contract separately left and right ECD, with 50% of maximal voluntary contraction force, for periods of 1-1.5 min. MEG-EMG coherence has been evaluated by Welch method, by windowing (Hamming) the artifact free signal in tracts lasting 2048 pt, overlapped by 60%. Tracts with high coherence were selected. Confidence limit was calculated and coherence levels above this value considered for motor control characterization. Comparison between dominant - non dominant hemispheric frequency coherence spectra and spatial coherence distribution has been performed. Preliminary results indicate in dominant hemisphere, a more concentrated frequency distribution in the coherence spectrum (higher values in a sharper frequency range) and, once selected the coherence at peck value, a more concentrated spatial distribution. Methodological optimization of the coherence procedure are discussed. These indications of dominant-non dominant hemispheric asymmetries could be feather investigated to establish physiological parameters to identify eventual alterations in the cortical motor organization induced by pathological conditions.