How ongoing neuronal oscillations account for evoked fMRI variability

Abstract

Variabilityofevoked single-trial responses despite constant input or task is a feature of large-scale brain signals recorded by fMRI. Initial evidencesignifiedrelevanceoffMRIsignalvariabilityforperceptionandbehavior.Yettheunderlyingintrinsic neuronalsourceshavenot been previously substantiated. Here, we address this issue using simultaneous EEG-fMRI and real-time classification of ongoing alpha-rhythm states triggering visual stimulationinhumansubjects.Weinvestigatedwhetherspontaneous neuronal oscillations-as reflected in the posterior alpha rhythm-account for variability of evoked fMRI responses. Based on previous work, we specifically hypothesized linear superposition of fMRI activity related to fluctuations of ongoing alpha rhythm and a visually evoked fMRI response. We observed that spontaneous alpha-rhythm power fluctuations largely explain evoked fMRI response variance in extrastriate, thalamic, and cere-bellar areas. For extrastriate areas,weconfirmed the linear superposition hypothesis. We hence linked evoked fMRI response variability to an intrinsic rhythm's power fluctuations. These findings contribute to our conceptual understanding of how brain rhythms can account for trial-by-trial variability in stimulus processing. © 2011 the authors.