Comparison of linear and nonlinear functional connectivity in alcoholic patients

Communication among individual neurons or neuronal populations, reflected by transient synchronous activity, is the core mechanism underlying the information processing of the brain. Although it is widely assumed that their interactions (i.e. functional connectivity) are highly nonlinear, the amount of nonlinear information transmission and its functional roles are not clear. In this study, we compare the linear functional connectivity measured by coherence and nonlinear functional connectivity estimated by nonlinear interdependence in 16-channel EEGs recorded from twelve alcoholic patients (age: 45.2 ± 7.6) exhibiting the abnormal cortical information processing and age-matched healthy subjects. The alcoholic patients showed an increase in alpha band EEG coherence, but a decrease in EEG coherences in delta, theta, and beta band among interhemispheric regions, compared with those of healthy subjects. In contrast, nonlinear interdependence was increased within right hemispheric regions, particularly left -to- right direction, in alcoholic patients. These results indicate that alcoholic patients exhibit dominant linear functional connections between intrahemispheric regions and dominance of nonlinear connections to or from right hemispheric regions. These finding suggest the clear presence of nonlinear functional connectivity, which cannot be detected by conventional coherence measures, and the possible functional significance of the information processing. These results indicate that alcoholic patients exhibit weak linear functional connections between interhemispheric regions and strong nonlinear connections in right hemispheric regions.