Cognitive reserve modulates task-induced activations and deactivations in healthy elders, amnestic mild cognitive impairment and mild Alzheimer's disease.
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.
Bosch
Beatriz
B
Alzheimer's Disease and Other Cognitive Disorders Unit, Neurology Service, Hospital Clínic de Barcelona, Catalonia, Spain.
Bartrés-Faz
David
D
Rami
Lorena
L
Arenaza-Urquijo
Eider M
EM
Fernández-Espejo
Davinia
D
Junqué
Carme
C
Solé-Padullés
Cristina
C
Sánchez-Valle
Raquel
R
Bargalló
Núria
N
Falcón
Carles
C
Molinuevo
José Luis
JL
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*
D010100:Oxygen