Effects of eyelid closure, blinks, and eye movements on the electroencephalogram

Objective To characterize the effects of the eyeball and eyelid positions during eyeblinks on electroencephalographic (EEG) potentials. Methods Movements of the upper eyelids and eyes were measured in two healthy subjects using the magnetic search coil technique during horizontal and vertical eye rotations, eyeblinks, and lid closure. Corresponding signal changes were recorded simultaneously on the electroencephalogram (EEG). Results Spontaneous blinks produced small eye movements directed down and inward, whereas slow or forced blinks were associated with delayed upward eye rotations (i.e. Bellʹs phenomenon); both types of blinks caused positive EEG potentials with bifrontal distribution maximum at Fp1 and Fp2. Conclusions In prior reports, these positive EEG artifacts have been attributed to upward eyeball rotation during blinks—Bellʹs phenomenon. By contrast, our findings indicate that movements of the eyelid contribute to a greater extent to these EEG potentials than do upward eyeball rotations. Significance Care is required in attributing EEG artifacts to movements of either eyeball or eyelid, since our findings suggest that they both contribute to these potentials.