Ongoing oscillations: how do they affect perception?

A growing number of evidences have shown that spontaneous brain activity influences behaviour. Specifically, a considerable portion of the trial-to-trial variability in visual perception can be accounted by parameters of ongoing oscillations as measured by EEG, such as power and phase in the α band [1]. A typical paradigm employs near-threshold stimuli; however, valuable insights may arise from the psychometric function, obtained by presenting a wider range of stimulus intensities [2]. In the present work, we describe a formal model with the aim of addressing the demanding issue of how pre-stimulus power and phase contribute to perception, in terms of underlying physiological mechanisms. Based on subthreshold oscillations features, we estimate the response probability of the system as a function of stimulus intensity: it showed a sigmoid shape, resembling the psychometric curve. We identified three main mechanisms in the neural population which affect the response probability function in a specific way: the amplitude of subthreshold oscillations, the degree of synchronization, and the excitation-inhibition balance. Since all these features may contribute to EEG power, in non-invasive studies they cannot be distinguished from each other. We hypothesize that changes observed behaviourally in the psychometric function would provide suggestions on the involved neurophysiological mechan isms.