Frontal Functional Connectivity Impairment in Early Stages of Alzheimer’s Disease

Abstract Background Many neurophysiological markers such as neuronal oscillations, cortical neuronal synchronization and long-range neuronal coupling have been suggested to permit the identification of early cognitive impairments in Alzheimer's disease (AD). However, it is still unclear whether alterations in long-range Functional Connectivity (FC) constitute part of early mechanisms in the initial stages of AD.MethodsEighteen participants (69-88 years old), classified as early AD and matching healthy controls, were evaluated while performing a virtual spatial navigation task. We combined electroencephalography (EEG) and eye movement recordings during the performance of a virtual version of the Morris Water Maze (VMWM), where participants had to find a submerged, invisible platform. The groups were compared in their navigation performance with different metrics of brain activity.ResultsWe found that the subjects of both groups showed characteristic visual exploration patterns, with a central and over the horizontal midline exploration in controls and more peripheral and sparse fixations, in early AD subjects. In addition, regions in visual exploration between the groups were significantly different. The control group presented a marked occipital activity in the beta band (15-20 Hz) in comparison to the early AD group at early processing time. These differences in the beta band were much more robust in prefrontal regions with significant differences in the frontal cortex, which has been associated with spatial navigation tasks in addition to planning and decision making.ConclusionsThese results suggest that long-range Functional connectivity networks generated from early visual activity contribute to the mechanisms involved in the loss of spatial encoding at the early stages of AD.