title: Brain signal variability is parametrically modifiable.
abstract: Moment-to-moment brain signal variability is a ubiquitous neural characteristic, yet remains poorly understood. Evidence indicates that heightened signal variability can index and aid efficient neural function, but it is not known whether signal variability responds to precise levels of environmental demand, or instead whether variability is relatively static. Using multivariate modeling of functional magnetic resonance imaging-based parametric face processing data, we show here that within-person signal variability level responds to incremental adjustments in task difficulty, in a manner entirely distinct from results produced by examining mean brain signals. Using mixed modeling, we also linked parametric modulations in signal variability with modulations in task performance. We found that difficulty-related reductions in signal variability predicted reduced accuracy and longer reaction times within-person; mean signal changes were not predictive. We further probed the various differences between signal variance and signal means by examining all voxels, subjects, and conditions; this analysis of over 2 million data points failed to reveal any notable relations between voxel variances and means. Our results suggest that brain signal variability provides a systematic task-driven signal of interest from which we can understand the dynamic function of the human brain, and in a way that mean signals cannot capture.
authors.affiliation: Max Planck Society-University College London Initiative for Computational Psychiatry and Ageing Research (ICPAR), Center for Lifespan Psychology, Max Planck Institute for Human Development, 14195 Berlin, Germany.
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Garrett
authors.affiliation: Rotman Research Institute, Toronto, Ontario, Canada M6A 2E1, Department of Psychology, University of Toronto, Toronto, ON, Canada M5S 3G3 and.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: McIntosh
authors.affiliation: Rotman Research Institute, Toronto, Ontario, Canada M6A 2E1, Department of Psychology, University of Toronto, Toronto, ON, Canada M5S 3G3 and Department of Psychiatry, University of Toronto, Toronto, ON, Canada M5T 1R8.
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Grady
mesh_terms: D000328:Adult; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D001931:Brain Mapping; D005145:Face; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D015999:Multivariate Analysis; D010100:Oxygen / Q000097:blood; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D017603:Signal Detection, Psychological; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: brain signal variability; fMRI; face processing; noise