Impairment of oscillatory activity in survivors of severe sepsis: a magnetoencephalography study

A number of studies suggest that the clinical manifestation of neurological deficits results from pathologically synchronized neuronal oscillations and altered oscillatory coupling in the brain. For example, aberrant neuronal synchronization was already shown in patients diagnosed with liver cirrhosis. Currently, more and more evidence has been given that former critical care patients, especially survivors of severe sepsis, endure long-lasting cognitive impairments. Sepsis survivors are known to frequently develop an encephalopathy, which is commonly considered as reversible, but profound knowledge is still lacking. In this study, 25 cirrhotic patients, 23 normal healthy controls and 26 sepsis survivors were included. Sepsis survivors were included either shortly, 6 or 12 months after ICU discharge. In these three groups, magnetoencephalography (MEG) data were collected at rest and during a visual task employing repetitive flicker stimulation. Resting MEG and evoked responses were analyzed. While normal, healthy controls showed the highest resting frequency, we observed a lower frequency in cirrhotic patients and sepsis survivors. In sepsis survivors, the lowest resting frequency was found at T0. Moreover, cirrhotic patients and sepsis survivors were not able to dynamically adapt to the visual flickering stimulation, i.e. coupling to flickering stimulation was significantly lower in the two patient groups in comparison to normal, healthy controls. Interestingly, coupling improved with the time after ICU discharge in sepsis survivors. These results indicate abnormal ongoing and event-related brain oscillations in HE patients and also in sepsis survivors. The findings analysing coupling to visual stimulation in particular suggest a lack of local cortical synchronization.