title: Task difficulty modulates young-old differences in network expression.
abstract: The extent of task-related fMRI activation can vary as a function of task difficulty. Also the efficiency or capacity of the brain networks underlying task performance can change with aging. We asked whether the expression of a network underlying task performance would differ as a function of task demand in old and young individuals. 26 younger and 23 older healthy adults performed a delayed item recognition task that used the response signal method to parametrically manipulate the extrinsic difficulty of the task by imposing five different deadlines for recognition response. Both age groups showed a speed-accuracy trade-off, but the younger group achieved greater discriminability at the longer deadlines. We identified a spatial pattern of fMRI activation during the probe phase whose expression increased as the response deadline shortened and the task became more difficult. This pattern was expressed to a greater degree by the old group at the long deadlines, when the task was easiest. By contrast, this pattern was expressed to a greater degree by the younger group at the short deadlines, when the task was hardest. This suggests reduced efficiency and capacity of this network in older subjects. These findings suggest that neuroimaging studies comparing task-related activation across groups with different cognitive abilities must be interpreted in light of the relative difficulty of the task for each group.
authors.affiliation: Cognitive Neuroscience Division of the Taub Institute for the Study of Alzheimer's Disease and the Aging Brain, Columbia University College ofPhysicians and Surgeons, 630 W 168th St, New York, NY 10032, USA. ys11@columbia.edu
authors.forename: Yaakov
authors.initials: Y
authors.lastname: Stern
authors.forename: Brian C
authors.initials: BC
authors.lastname: Rakitin
authors.forename: Christian
authors.initials: C
authors.lastname: Habeck
authors.forename: Yunglin
authors.initials: Y
authors.lastname: Gazes
authors.forename: Jason
authors.initials: J
authors.lastname: Steffener
authors.forename: Arjun
authors.initials: A
authors.lastname: Kumar
authors.forename: Aaron
authors.initials: A
authors.lastname: Reuben
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D011930:Reaction Time; D021641:Recognition, Psychology; D013997:Time Factors; D055815:Young Adult
chemical_list: D010100:Oxygen