title: Stimulus set meaningfulness and neurophysiological differentiation: a functional magnetic resonance imaging study.
abstract: A meaningful set of stimuli, such as a sequence of frames from a movie, triggers a set of different experiences. By contrast, a meaningless set of stimuli, such as a sequence of 'TV noise' frames, triggers always the same experience--of seeing 'TV noise'--even though the stimuli themselves are as different from each other as the movie frames. We reasoned that the differentiation of cortical responses underlying the subject's experiences, as measured by Lempel-Ziv complexity (incompressibility) of functional MRI images, should reflect the overall meaningfulness of a set of stimuli for the subject, rather than differences among the stimuli. We tested this hypothesis by quantifying the differentiation of brain activity patterns in response to a movie sequence, to the same movie scrambled in time, and to 'TV noise', where the pixels from each movie frame were scrambled in space. While overall cortical activation was strong and widespread in all conditions, the differentiation (Lempel-Ziv complexity) of brain activation patterns was correlated with the meaningfulness of the stimulus set, being highest in the movie condition, intermediate in the scrambled movie condition, and minimal for 'TV noise'. Stimulus set meaningfulness was also associated with higher information integration among cortical regions. These results suggest that the differentiation of neural responses can be used to assess the meaningfulness of a given set of stimuli for a given subject, without the need to identify the features and categories that are relevant to the subject, nor the precise location of selective neural responses.
authors.affiliation: Department of Neurology, University of Wisconsin, Madison, Wisconsin, United States of America; Department of Psychiatry, University of Wisconsin, Madison, Wisconsin, United States of America.
authors.forename: Melanie
authors.initials: M
authors.lastname: Boly
authors.affiliation: Department of Psychiatry, University of Wisconsin, Madison, Wisconsin, United States of America.
authors.forename: Shuntaro
authors.initials: S
authors.lastname: Sasai
authors.affiliation: Department of Psychiatry, University of Wisconsin, Madison, Wisconsin, United States of America; Coma Science Group, Cyclotron Research Centre and Department of Neurology, University of Liege and CHU Sart Tilman Hospital, Liege, Belgium.
authors.forename: Olivia
authors.initials: O
authors.lastname: Gosseries
authors.affiliation: Department of Psychiatry, University of Wisconsin, Madison, Wisconsin, United States of America; Riken Brain Science Institute, Tokyo, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Oizumi
authors.affiliation: Department of Biomedical and Clinical Sciences 'Luigi Sacco', University of Milan, Milan, Italy.
authors.forename: Adenauer
authors.initials: A
authors.lastname: Casali
authors.affiliation: Department of Biomedical and Clinical Sciences 'Luigi Sacco', University of Milan, Milan, Italy; Instituto Di Ricovero e Cura a Carattere Scientifico, Fondazione Don Carlo Gnocchi, Milan, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Massimini
authors.affiliation: Department of Psychiatry, University of Wisconsin, Madison, Wisconsin, United States of America.
authors.forename: Giulio
authors.initials: G
authors.lastname: Tononi
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009040:Motion Pictures; D010775:Photic Stimulation