In the blink of an eye: The contribution of microsaccadic activity to the induced gamma band response

In 2008 an article by Yuval-Greenberg and colleagues initiated a lively debate within the field of induced gamma band research. Their article suggested that scalp-recorded induced gamma band responses (iGBRs) to visual stimuli could be obscured by minute movements of extraocular muscles, called microsaccades, which are associated with the saccadic spike potentials (SPs). Yuval-Greenberg et al. (2008) proposed that the temporal and spectral characteristics of SPs could mask and have been previously mistaken for cortical induced gamma band activity. This review summarises the main findings of the report by Yuval-Greenberg et al. (2008) and the research that has emerged since its publication. Microsaccades and the associated SP waveforms are described in detail and their contribution to the iGBR discussed. Different lines of argument are considered that suggest that the scalp-recorded iGBR exists separate from ocular contributions. The article then considers techniques that are widely used to remove electroencephalogram (EEG) artefacts and their potential adaptation for the removal of SPs. The review closes by pointing to future directions that researchers may explore in order to disentangle neural iGBRs and artefactual, SP-related iGBRs, and to several routes which researchers may consider in order to increase the informative value of their scalp-recorded iGBR data. We conclude that further investigation and testing is necessary to develop signal processing tools that successfully identify and correct SPs in EEG data without distorting the neural iGBR. (C) 2010 Elsevier B.V. All rights reserved.