Scalp Distribution of Magnetic Fields Generated by Horizontal Eye Movements and Eye Blinks
Eye movements are known to produce artifacts in the electroencephalogram (EEG) and in the magnetoencephalogram (MEG) which can result in substantial distortions of the morphology of sensory-evoked waveforms (Antervo et al., 1985; Katila et al., 1981; Vaughan, 1969). Some studies are more susceptible to these artifacts. For example, certain studies require peripheral presentations of visual stimuli which tend to evoke unwanted, foveating eye movements, from untrained subjects. The application of MEG to neurological diagnosis and basic neuroscience research requires the assessment of possible contamination of surface-recorded electromagnetic fields (ERFs) by time-locked ocular and myogenic activity such as eye movements and eye blinks. Three types of electrical potentials associated with eye movements have been identified; the antecedent slow activity (Kurtzberg and Vaughan 1977), the spike potential (Riemslag et al., 1988) and the lambda wave (Gaarder et a1.,1964). The spike potential (SP) has maximal amplitude near the orbital regions and seems to originate in the oculomotor neurons innervating the ocular muscle units (Riemslag et al., 1988). However, the retino-corneal potential which has been the primary concern of eye movement artifacts in evoked potential studies (Vaughan Jr., 1969) also contributes to the spike potential.
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