Induced gamma band responses in human EEG after the control of miniature saccadic artifacts.

Induced gamma band responses (iGBRs) in the human electroencephalogram (EEG) have been ascribed to the activation of cortical object representations. Recently, this claim was challenged and it was stated that iGBRs occurring in the time window between 200 and 350 ms after stimulus onset are, to a great extent, generated by an electromyogenic artifact caused by miniature saccades (MS). In the present paper we focus on the characterization of iGBRs during the activation of cortical object representations, when recordings have been controlled for saccade-related transient potentials. For this we present an algorithm for the correction of saccade-related transient potentials (COSTRAP) which identifies and notably suppresses transient spike potentials (TSPs) that are likely to be linked to MSs. Furthermore, we conducted an EEG study to demonstrate (1) the feasibility of the algorithm, (2) the cortical origin iGBRs and (3) their relation to cortical object representations. Our results revealed that (i) it is possible to isolate TSPs, (ii) the morphology of the cleansed iGBR cannot be explained by an underlying myogenic artifact and (iii) the remaining iGBRs are sensitive to object recognition. Therefore we conclude that, with saccadic artifacts being controlled, high-frequency oscillations in human EEG are reliable electrophysiological correlates of cognitive processes.