FMRI correlates of pathologically changed alpha rhythm in patients with hepatic encephalopathy

Objective: The simultaneous combination of EEG and fMRI has recently been shown to be capable of providing maps which are functionally related to the classical posterior alpha rhythm in healthy subjects (Laufs et al. 2003). It has been reported (Kullmann et al. 2001) that patients with hepatic encephalopathy have altered topoography of EEG background rhythms. Here we investigate fMRI correlates of pathologically changed alpha activity in ten patients (mean age 47 years, range 39–53) with hepatic encephalopathy. Methods: Patients were lying in the dark bore of a 1.5 T MR tomograph. EEG was recorded from 29 scalp positions using an MR-compatible EEG amplifyer and 32 channel EEG cap including one EOG and two ECG electrodes. Patients were asked to stay awake and to be relaxed with eyes closed during the whole experiment. No other task was provided. Functional MRI (BOLD sensitive gradient echo planar imaging sequence, TR=2 s, TA=1650 ms, 16 slices) and EEG (sampling frequency 5000 Hz) were acquired simultaneously. To obtain continuous EEG signal, artifacts related to MR-acquisition were corrected using an algorithm proposed by Allen et al. (Allen et al. 2000). Results & Discussion: SPM group analysis (random effects N=10) yielded significant (p<0.01, uncorrected) alpha rhythm associated negative BOLD signal in the occipital cortex which is in concordance with former results by our and other groups (Moosmann et al. 2003). However, alpha activity associated negative BOLD signal in the patients group was maximal in the frontal cortex bilaterally, where no significant signal was found for healthy subjects. These results agree with electrophysiological findings of a anteriorized alpha rhythm in patients with hepatic encephalopathy (Kullmann et al. 2001). Conclusions: Simultaneous EEG-fMRI provides maps of areas which are involved in alpha rhythm generation. An occipital-to-frontal shift of alpha activity in patients with hepatic encephalopathy is associated with an occipital-to-frontal shift of maximal negative BOLD signal in fMRI. * This work was supported by the Federal Ministry for Education and Research BMBF (Berlin Neuroimaging Center).

Keywords: Enzephalopathie, Leberzirrhose, funktionelles MRT