title: Interhemispheric coupling improves the brain's ability to perform low cognitive demand tasks in Alzheimer's disease and high cognitive demand tasks in normal aging.
abstract: OBJECTIVE
  Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects the corpus callosum (CC), which plays a key role in interhemispheric coupling in high-demand conditions. Using 3D callosal measurements and a letter-matching paradigm, this 2-part study investigated the neural substrate of interhemispheric coupling in individuals with AD or amnestic mild cognitive impairment (a-MCI) and age-matched healthy individuals (HC).
  
  
  METHODS
  Thirty-three right-handed participants were MRI scanned to measure the volume of the CC in 5 sections. In Study 1, AD, a-MCI, and HC individuals performed a low-demand perceptual letter shape-matching task (e.g., A-A); in Study 2, a-MCI and HC individuals performed a "case-sensitive" letter-matching task (Study 2A) and a "load-sensitive" letter-matching task (Study 2B).
  
  
  RESULTS
  The results showed a positive correlation between Response Times and the midbody of the CC at the lowest cognitive demand level (Study 1) in participants with AD, and the total CC, midbody, caudal body, and isthmus of the CC at high cognitive demand levels (Study 2A) in normal aging. The volume of the anterior part of the CC was significantly negatively correlated with the interhemispheric behavioral indices for the a-MCI group (Study 1 and Study 2B).
  
  
  CONCLUSIONS
  This study provides evidence that interhemispheric coupling may constitute a flexible mechanism that can improve the brain's ability to meet processing demands for low cognitive demand in AD and for high cognitive demand in normal aging.
authors.affiliation: Institut Universitaire de Gériatrie de Montréal, and Université de Montréal, Quebec, Canada. jennyfer.ansado@umontreal.ca
authors.forename: Jennyfer
authors.initials: J
authors.lastname: Ansado
authors.forename: Louis
authors.initials: L
authors.lastname: Collins
authors.forename: Sven
authors.initials: S
authors.lastname: Joubert
authors.forename: Vladimir
authors.initials: V
authors.lastname: Fonov
authors.forename: Oury
authors.initials: O
authors.lastname: Monchi
authors.forename: Simona Maria
authors.initials: SM
authors.lastname: Brambati
authors.forename: Francesco
authors.initials: F
authors.lastname: Tomaiuolo
authors.forename: Michael
authors.initials: M
authors.lastname: Petrides
authors.forename: Sylvane
authors.initials: S
authors.lastname: Faure
authors.forename: Yves
authors.initials: Y
authors.lastname: Joanette
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D000544:Alzheimer Disease / Q000150:complications* / Q000473:pathology / Q000523:psychology*; D000704:Analysis of Variance; D003072:Cognition Disorders / Q000209:etiology* / Q000473:pathology; D003337:Corpus Callosum / Q000473:pathology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D013223:Statistics as Topic