BrainLayer: the multilayer brain networks underlying cognitive decline
Cognitive deterioration in lesional brain disease, such as cerebrovascular accidents, multiple sclerosis and glioma, weighs heavily on patients, their caregivers and society, particularly since curative treatment is unavailable. Variation in cognitive decline is large: some patients suffer from progressive deterioration, while others do not, despite comparable disease parameters. Using concepts from graph theory, cognition is increasingly seen as a combination of segregation and integration occurring in the brain network. This network can be measured anatomically and functionally using neuroimaging and neurophysiological modalities. Brain regions form the network nodes, while their number of interconnections and/or extent of functional interdependency define connections. Acute and long-term cognitive decline have been linked to unimodal brain network alterations. However, optimal cognitive functioning in the setting of disease depends on a complex combination of resilience in the form of maintained connectivity despite lesioning, but adaptivity, plasticity or even compensation in the context of continuing cognitive demands. However, ‘traditional’ neuroscientific approaches have not led to accurate operationalization of these processes. In BrainLayer, the theoretical framework of multilayer network theory will be used to synergize multimodal characteristics of connectivity patterns into a single marker of cognitive functioning. Notably, multilayer network characterization supersedes the summation of unilayer characteristics when trying to describe the behavior of the entire system, which may prove essential to sensitively and specifically pick up on individual variation in cognitive functioning. Furthermore, the project will leverage several longitudinal study designs to assess multilayer networks and cognitive decline as a result of on the one hand controlled ‘virtual lesions’ induced with transcranial magnetic stimulation, and on the other hand recurrent/progressive lesional brain disease. Taken together, BrainLayer aims to elucidate individual resilience and adaptivity of the brain network in the context of lesional brain disease, thereby allowing for more accurate understanding and possibly prediction of cognitive decline.