Abstract
Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) are the two most popular non-invasive methods used to study the neural mechanisms underlying human cognition. These approaches are considered complementary: fMRI has higher spatial resolution but sluggish temporal resolution, whereas EEG has millisecond temporal resolution, but only at a broad spatial scale. Beyond the obvious fact that fMRI measures properties of blood and EEG measures changes in electric fields, many foundational studies assume that, aside from differences in spatial and temporal precision, these two methods index the same underlying neural modulations. We tested this assumption by using EEG and fMRI to measure attentional modulations of neural responses to stimuli of different visual contrasts. We found that equivalent experiments performed using fMRI and EEG on the same participants revealed remarkably different patterns of attentional modulations: event-related fMRI responses provided evidence for an additive increase in responses across all contrasts equally, whereas early stimulus-evoked event-related potentials (ERPs) showed larger modulations with increasing stimulus contrast and only a later negative-going ERP and low-frequency oscillatory EEG signals showed effects similar to fMRI. These results demonstrate that there is not a one-to-one correspondence between the physiological mechanisms that give rise to modulations of fMRI responses and the most commonly used ERP markers, and that the typical approach of employing fMRI and EEG to gain complementary information about localization and temporal dynamics is over-simplified. Instead, fMRI and EEG index different physiological modulations and their joint application affords synergistic insights into the neural mechanisms supporting human cognition.
Acknowledgments & author contributions
SI and TCS conceived, implemented the experiments, collected and analyzed the data, and cowrote the manuscript. JTS conceived and supervised the project and co-wrote the manuscript. Funding was provided by NIH R01-EY025872 (J.T.S.), the James S. McDonnell Foundation (J.T.S), the Howard Hughes Medical Institute International program (S.I.), a Royal Thai Scholarship from the Ministry of Science and Technology in Thailand (S.I.), NIH T32-MH020002 (T.C.S.), NIH T32-EY007136 (T.C.S.), and NIH F32-EY023438 (T.C.S.).