Zoë Tieges

Source localization of event-related potential effects differentiates between vascular dementia and Alzheimer's disease

Background: VaD and AD have different underlying pathogenic mechanisms, and may produce distinct signatures in brain activity that could aid in differential diagnosis. We investigate possible differential markers based on source localization of electrophysiological correlates of memory processing in VaD and AD. Methods: Advances in high resolution whole head EEG recordings, together with accurate conductivity models of head tissues, mean that reasonably accurate distributed source models can now be established. We used 128-channel EEG to measure amplitudes, latencies and topographies of the N2, P4, and P7 in AD and VaD patients and controls during an episodic memory task (all groups N = 8). We then used source localization methods (GeoSource; LAURA) to determine the cortical generators for the best performing ERP diagnostic markers. Results: The posterior N2 is prominent in controls and AD, but attenuated in VaD. This N2 effect localizes to the central occipital cortex in AD and controls, but not in VaD. The prefrontal P4 is prominent in controls, and evident in VaD, but attenuated in AD. The P4 localizes in all groups to the medial temporal region, but with varying intensity and timing. The right parietal P7 effect is prominent in controls, but attenuated in AD and VaD. The P7 localizes to prefrontal cortex in controls, but involves only right posterior cortex in VaD, and central posterior cortex in AD. Conclusions: Source localization analysis shows that scalp ERP differences between AD and VaD can be unambiguously attributed to different underlying generators within the brain. We hypothesize that these effects reflect disease-specific neuropathology, and offer new functional biomarkers to aid in differential diagnosis of AD and VaD.