Hepatic encephalopathy is associated with slowed and delayed stimulus-associated somatosensory alpha activity

Objective: Hepatic encephalopathy (HE) is associated with motor symptoms and attentional deficits, which are related to pathologically slowed oscillatory brain activity. Here, potential alterations of oscillatory activity in the somatosensory system were investigated. Methods: 21 patients with liver cirrhosis and varying HE severity and 7 control subjects received electrical stimulation of the right median nerve while brain activity was recorded using magnetoencephalography (MEG). Oscillatory activity within the contralateral primary somatosensory cortex (S1) and its stimulus-induced modulation were analyzed as a function of disease severity. Results: Median nerve stimuli evoked an early broadband power increase followed by suppression and then rebound of S1 alpha and beta activity. Increasing HE severity as quantified by the critical flicker frequency (CFF) was associated with a slowing of the alpha peak frequency and a delay of the alpha rebound. Conclusion: The present results provide the first evidence for a slowing of oscillatory activity in the somatosensory system in HE in combination with a previously unknown deficit of S1 in adjusting activation levels back to baseline. Significance: These findings advance the understanding of the manifold symptoms of HE by strengthening the theory that disease related slowing of oscillatory brain activity also affects the somatosensory system. (C) 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.