Background: Synchronization can measure the interaction between different brain regions, but how alcoholics and non-alcoholic subjects differ in synchronization is still not fully clear.

Methods: The synchronization analyses in present study on EEG synchronization are almost all based on the scalp EEG data. However, due to the volume conductor effect, there may be pseudo relevance between the scalp electrodes, which further affects the measurement of synchronization. Based on eLORETA and the self-defined regions of interest (ROIs), the synchronization between ROIs was measured. Our study used synchronization likelihood to measure the synchronization difference between 28 alcoholics and 28 controls (nonalcoholics) during certain cognitive tasks based on the scalp EEG and the cortical ROI.

Results: The results indicated that the synchronization for the alcoholic group is lower in multiple bands than in the control group when performing the same cognitive task. Moreover, the synchronization for the control group can reflect the complexity levels of the cognitive tasks, whereas the alcoholics only display erratic changes.

Conclusions: These two results indicate that in alcoholics, brain synchronization is reduced, and the connection between different brain regions is inhibited, meaning brain cognitive function is impaired. In addition, the synchronization method based on the cortical ROI is more effective and more valuable than the scalp EEG. Our research provides strong evidence that long-term alcoholism causes functional damage to the brain from an entirely new perspective.

From our results, the synchronization method based on the cortical ROI is more effective and more valuable than the scalp EEG. During the same cognitive tasks, the alcoholics have almost lower brain synchronization than the controls. During tasks with different complexity levels, the brain synchronization for the controls increases corresponding to the complexity levels, whereas for the alcoholics, it only demonstrates erratic changes. The MSL for the controls can sensitively reflect the subtle complexity difference for cognitive tasks, the alcoholics cannot. The study provides strong evidence that long-term alcoholism maybe causes functional damage to the brain.