We studied movement-related EEG oscillatory changes in the alpha, beta and low-gamma frequency bands in three different paradigms of movement, namely ballistic, sustained, and negative (muscle relaxation). A time-frequency analysis of non-phase-locked activity in the 7-47 Hz range was performed on movement-centred EEG sweeps using wavelet filters and Gabor transforms. All three movements were accompanied by a decrease in beta activity that began contralaterally about 1.5 s prior to the onset of movement but that extended to both sides near the beginning of the movement. This decrease was followed by a rebound after the end of the movement in the ballistic and negative movements. A decrease was also seen in the alpha band during the three paradigms, which began later (1 s before movement) and lasted longer. An increase in gamma activity was only seen during ballistic and sustained movements, while a decrease in gamma energy was observed during negative movements. It was concluded that changes in the beta band of the EEG before movement are related to the preparation for the movement, but an important afferent component may be present in the later changes. Gamma band activity may be just involved in the execution of the movement, related to muscle contraction.
The techniques of cognitive evoked potentials are considered long and technically complex, which is why their use in clinical practice is not very widespread in spite of their potential utility. Recent advances in registering and analysis, together with improvement of the software managing these signals, have appreciably reduced these problems. Mismatch negativity stands out as the most promising of all the cognitive potentials due to its special characteristics regarding its generation requisites and its proven clinical utility. The fact that it can be generated without care requirements makes it especially useful for evaluating subjects with a low level of consciousness; it serves for predicting when they will emerge from a coma, amongst other uses. The incorporation of this technique into the arsenal of neurophysiological techniques for evaluating the state of these subjects will bring a substantial improvement in the evaluation of cases whose management in clinical practice is extremely complex.
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