title: Functional connectivity in mild cognitive impairment during a memory task: implications for the disconnection hypothesis.
abstract: Mild cognitive impairment (MCI) has been considered an intermediate state between healthy aging and dementia. The early damage in anatomical connectivity and progressive loss of synapses that characterize early Alzheimer's disease suggest that MCI could also be a disconnection syndrome. Here, we compare the degree of synchronization of brain signals recorded with magnetoencephalography from patients (22) with MCI with that of healthy controls (19) during a memory task. Synchronization Likelihood, an index based on the theory of nonlinear dynamical systems, was used to measure functional connectivity. During the memory task patients showed higher interhemispheric synchronization than healthy controls between left and right -anterior temporo-frontal regions (in all studied frequency bands) and in posterior regions in the γ band. On the other hand, the connectivity pattern from healthy controls indicated two clusters of higher synchronization, one among left temporal sensors and another one among central channels. Both of them were found in all frequency bands. In the γ band, controls showed higher Synchronization Likelihood values than MCI patients between central-posterior and frontal-posterior channels and a high synchronization in posterior regions. The inter-hemispheric increased synchronization values could reflect a compensatory mechanism for the lack of efficiency of the memory networks in MCI patients. Therefore, these connectivity profiles support only partially the idea of MCI as a disconnection syndrome, as patients showed increased long distance inter-hemispheric connections but a decrease in antero-posterior functional connectivity.
authors.affiliation: Laboratory of Cognitive and Computational Neuroscience, Center of Biomedical Technology, Madrid, Spain. ricbajo@gmail.com
authors.forename: Ricardo
authors.initials: R
authors.lastname: Bajo
authors.forename: Fernando
authors.initials: F
authors.lastname: Maestú
authors.forename: Angel
authors.initials: A
authors.lastname: Nevado
authors.forename: Miguel
authors.initials: M
authors.lastname: Sancho
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gutiérrez
authors.forename: Pablo
authors.initials: P
authors.lastname: Campo
authors.forename: Nazareth P
authors.initials: NP
authors.lastname: Castellanos
authors.forename: Pedro
authors.initials: P
authors.lastname: Gil
authors.forename: Stephan
authors.initials: S
authors.lastname: Moratti
authors.forename: Ernesto
authors.initials: E
authors.lastname: Pereda
authors.forename: Francisco
authors.initials: F
authors.lastname: Del-Pozo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D054022:Cerebrum / Q000502:physiology* / Q000503:physiopathology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods; D008568:Memory / Q000502:physiology*; D009415:Nerve Net / Q000473:pathology / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*