title: Cognitive reserve modulates task-induced activations and deactivations in healthy elders, amnestic mild cognitive impairment and mild Alzheimer's disease.
abstract: BACKGROUND
  Cognitive reserve (CR) reflects the capacity of the brain to endure neuropathology in order to minimize clinical manifestations. Previous studies showed that CR modulates the patterns of brain activity in both healthy and clinical populations. In the present study we sought to determine whether reorganizations of functional brain resources linked to CR could already be observed in amnestic mild cognitive impairment (a-MCI) and mild Alzheimer's disease (AD) patients when performing a task corresponding to an unaffected cognitive domain. We further investigated if activity in regions showing task-induced deactivations, usually identified as pertaining to the default-mode network (DMN), was also influenced by CR.
  
  
  METHODS
  Fifteen healthy elders, 15 a-MCI and 15 AD patients underwent functional magnetic resonance imaging (fMRI) during a speech comprehension task. Differences in the regression of slopes between CR proxies and blood-oxygen-level dependent (BOLD) signals across clinical groups were investigated for activation and deactivation areas. Correlations between significant fMRI results and a language comprehension test were also computed.
  
  
  RESULTS
  Among a-MCI and AD we observed positive correlations between CR measures and BOLD signals in task-induced activation areas directly processing speech, as well as greater deactivations in regions of the DMN. These relationships were inverted in healthy elders. We found no evidence that these results were mediated by gray matter volumes. Increased activity in left frontal areas and decreased activity in the anterior cingulate were related to better language comprehension in clinical evaluations.
  
  
  CONCLUSIONS
  The present findings provide evidence that the neurofunctional reorganizations related to CR among a-MCI and AD patients can be seen even when considering a preserved cognitive domain, being independent of gray matter atrophy. Areas showing both task-induced activations and deactivations are modulated by CR in an opposite manner when considering healthy elders versus patients. Brain reorganizations facilitated by CR may reflect behavioral compensatory mechanisms.
authors: Alzheimer's Disease and Other Cognitive Disorders Unit, Neurology Service, Hospital Clínic de Barcelona, Catalonia, Spain.
authors: Beatriz
authors: B
authors: Bosch
authors: David
authors: D
authors: Bartrés-Faz
authors: Lorena
authors: L
authors: Rami
authors: Eider M
authors: EM
authors: Arenaza-Urquijo
authors: Davinia
authors: D
authors: Fernández-Espejo
authors: Carme
authors: C
authors: Junqué
authors: Cristina
authors: C
authors: Solé-Padullés
authors: Raquel
authors: R
authors: Sánchez-Valle
authors: Núria
authors: N
authors: Bargalló
authors: Carles
authors: C
authors: Falcón
authors: José Luis
authors: JL
authors: Molinuevo
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000473:pathology / Q000503:physiopathology*; D001921:Brain / Q000473:pathology / Q000502:physiology / Q000503:physiopathology*; D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000473:pathology / Q000503:physiopathology*; D032882:Comprehension / Q000502:physiology*; D005260:Female; D006304:Health Status; D006801:Humans; D007807:Language Tests; D008279:Magnetic Resonance Imaging; D008297:Male; D036421:Nerve Fibers, Unmyelinated / Q000473:pathology / Q000502:physiology; D009434:Neural Pathways / Q000473:pathology / Q000502:physiology / Q000503:physiopathology; D009483:Neuropsychological Tests; D009929:Organ Size; D010100:Oxygen / Q000097:blood; D012044:Regression Analysis; D012815:Signal Processing, Computer-Assisted; D013067:Speech Perception / Q000502:physiology*
chemical_list: D010100:Oxygen