Altered directed connectivity in patients with early vascular dementia during a visual oddball task

The altered functional connectivity in the brain of patients with early vascular dementia (VaD) is poorly understood. Here we investigated the directed connectivity differences between VaD and normal elderly while performing a visual oddball task. Multichannel EEG data during a visual oddball task were recorded for 12 patients with early VaD and 12 age, gender and education matched healthy elderly. Directed transfer function was used to investigate the directed connectivity of brain during pre-stimulus and post-stimulus periods in delta, theta, alpha and beta frequency bands. Significantly reduced inter-hemispheric connectivity was found in patients with early VaD compared to normal elderly in the delta and theta frequency bands during the pre-stimulus period. During the post-stimulus period, besides the decreased inter-hemispheric connectivity, significantly decreased parietal-to-frontal/central connectivity was also found in VaD compared to normal elderly in the delta frequency band. In addition to the decreased connectivity in VaD, significantly increased connectivity was also found both in the pre-stimulus and post-stimulus periods. These results suggest that pathophysiology changes in early VaD may cause the altered directed connectivity of the brain network. Our observations demonstrate the altered brain connectivity of early VaD and reveal impairment and compensation co-exist in patients with early VaD.