Coupling of functional magnetic resonance imaging and electroencephalography: Blood oxygen level dependent signal correlates of the alpha rhythm

Concurrent recording of Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has great potential for clinical and scientific neurological applications as it allows for the construction of functional MRI data linked temporally to the ongoing EEG. Such simultaneous recordings are challenging because EEG is prone to large artifacts induced by both the static and the time-variant fields of the MR scanner. I present a method for recording EEG and fMRI simultaneously, here termed Simultaneous Imaging for Tomographic Electrophysiology (SITE), and use it to localize fMRI correlates of the alpha rhythm in normal subjects as well as inter-ictal discharges in subjects with epilepsy.; Various hardware and software techniques were developed and tested. EEG was recorded using twisted dual-lead electrodes in a bipolar montage, to reduce MR field-related artifacts. Sharp low-pass filters ensured amplifiers did not saturate due to MR gradients and radio-frequency pulses. Ballistocardiogram, an artifact due to the pulse-related translation of the leads in the static MR field, was greatly reduced using an adaptive filter triggered by the subject's electrocardiogram.; The first design of the EEG system traded off MR slice coverage and visible EEG. In a second system, artifacts in the EEG due to time-variant MR fields were removed by triggering EEG acquisition off the MR imager with each scan TR, thus synchronizing the EEG and MRI clocks. An artifact template, formed by averaging epochs of EEG equal to the TR, was subtracted from the raw EEG. No significant difference was found between EEG recorded during whole brain fMRI and EEG recorded without scanning.; SITE maps of brain regions whose MRI signal changed reliably with modulation of the 8–13 Hz EEG alpha rhythm, present when a subject is awake with eyes closed, showed negative correlations between fMRI signal and alpha power in broad regions of occipital, parietal, and frontal cortex. Positive correlations were found in thalamus, and in one of two studies, insula. These results agree with prior human and animal studies relating alpha activity synchronization to decreased cortical activity. They may also explain changes in resting baseline fMRI signal. SITE maps of inter-ictal discharges showed fMRI correlates in suspected epileptogenic regions.