Chapter 55 High resolution EEG of sensorimotor brain functions: mapping ERPs or mu ERD?

Abstract

Electroencephalography (EEG) is a neuroimaging technique. Movement-related potentials (MRPs) reflect EEG components time- and phase-locked to the movement, nonphase-locked EEG components being attenuated by the averaging. Prestimulus EEG amplitude affects event related potentials (ERPs) and the ERPs might result from a nonlinear transformation of the concomitant phase-locked EEG oscillations. MRPs depend on the cerebellar inputs. MRPs are absent with dyssynergia cerebellaris myoclonica and lesions of dentate nucleus or superior cerebellar peduncle. MRPs are normal with cerebellar cortical degeneration. Sensorimotor events also result in desynchronization/synchronization (ERD/ERS) of nonphase-locked central EEG oscillations. The ERD/ERS of alpha- and beta-bands (mu rhythm) starts in frontomesial and contralateral central areas and in ipsilateral central area close to the movement onset. Mu ERD arises from MI-S1 and supplementary motor area (SMA), as indicated by magnetoencephalography (MEG) and high-resolution EEG studies. Following the movement offset, alpha and beta ERS has been the maximum in contralateral central-parietal areas overlying contralateral M1-S1. Scalp mu ERD begins more focally and ends more widespread than MRPs. Cortical sites responsive to electrical stimulation fit those generating MRPs, but not always those generating mu ERD. In the EEG study mentioned in this chapter, the stress is on the different topography of human mu MRPs and ERD related to unilateral right finger movements in a self-paced movement paradigm and in visuomotor tasks. During unilateral sensorimotor tasks, mu ERD reflects changes in the background oscillatory areas over primary and nonprimary cortical sensorimotor areas, including the posterior parietal activity, whereas MRPs represent increased, task-specific responses of SMA and contralateral M1-S1. MRPs are sensitive to spatio-temporal features of the cortical information processes. The chapter discusses the Mu ERD/ERS opening/closing of modality-specific thalamocortical channels. ERPs and MRPs reveal decreased excitation or disfacilitation of neural networks at the “closure” of the task-specific cortical processes.