Stephen D. Mayhew1, Karen J. Mullinger2, Camillo Porcaro3, 4, Richard W. Bowtell2, Andrew P. Bagshaw1, Susan T. Francis2
1BUIC, School of Psychology, University of Birmingham, Birmingham, United Kingdom; 2SPMMRC, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom; 3Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom; 4LETs-ISTC-CNR, Fatebenefratelli Hospital-Isola Tiberina, Rome, Italy
Conventional GLM analyses of fMRI data localise brain activity from the average stimulus response, ignoring trial-by-trial variability which is most relevant to the dynamics of brain function and behavioural outcomes. We combine data from visual, motor and somatosensory tasks to show that single-trial responses across the whole brain are concurrently modulated with activity in the stimulated primary sensory cortex. These modulations induce a positive correlation between single-trial positive and negative BOLD responses, despite a negative correlation between the average response magnitudes. These findings demonstrate that stimulus modulations extend over a far greater extent of the brain than previously suspected.