How Can We Differentiate Narrow-Band Oscillations from Aperiodic Activity?

Human intracranial recordings are composed of both periodic “narrow-band oscillations” along with aperiodic, “1/f-like”, activity. While oscillations have been a consistent focus of investigation in neurophysiological data, the physiological and functional properties of aperiodic activity are less well understood, as it is often treated as “background noise”. In this chapter, we provide an overview of both periodic and aperiodic activity, providing a brief historical perspective on the study of each, along with conceptual approaches and analytic assumptions researchers have made when measuring both types of activity. We then highlight recent methodological developments and available techniques for explicitly measuring (a)periodic activity, so as to evaluate which components of the neural data are changing. We propose that studies of human intracranial recordings should employ measures which can differentiate (a)periodic signals in order to determine if they have distinct generators and functional roles. Finally, we discuss putative interpretations of both periodic and aperiodic activity, as well as several unresolved issues which can be explored in future work to further model and interpret these signals.