title: Brain signal complexity rises with repetition suppression in visual learning.
abstract: Neuronal activity associated with visual processing of an unfamiliar face gradually diminishes when it is viewed repeatedly. This process, known as repetition suppression (RS), is involved in the acquisition of familiarity. Current models suggest that RS results from interactions between visual information processing areas located in the occipito-temporal cortex and higher order areas, such as the dorsolateral prefrontal cortex (DLPFC). Brain signal complexity, which reflects information dynamics of cortical networks, has been shown to increase as unfamiliar faces become familiar. However, the complementarity of RS and increases in brain signal complexity have yet to be demonstrated within the same measurements. We hypothesized that RS and brain signal complexity increase occur simultaneously during learning of unfamiliar faces. Further, we expected alteration of DLPFC function by transcranial direct current stimulation (tDCS) to modulate RS and brain signal complexity over the occipito-temporal cortex. Participants underwent three tDCS conditions in random order: right anodal/left cathodal, right cathodal/left anodal and sham. Following tDCS, participants learned unfamiliar faces, while an electroencephalogram (EEG) was recorded. Results revealed RS over occipito-temporal electrode sites during learning, reflected by a decrease in signal energy, a measure of amplitude. Simultaneously, as signal energy decreased, brain signal complexity, as estimated with multiscale entropy (MSE), increased. In addition, prefrontal tDCS modulated brain signal complexity over the right occipito-temporal cortex during the first presentation of faces. These results suggest that although RS may reflect a brain mechanism essential to learning, complementary processes reflected by increases in brain signal complexity, may be instrumental in the acquisition of novel visual information. Such processes likely involve long-range coordinated activity between prefrontal and lower order visual areas.
authors.affiliation: Université de Montréal, Département de psychologie, Montreal, QC H3C 3J7, Canada; CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada. Electronic address: marc.philippe.lafontaine@umontreal.ca.
authors.forename: Marc Philippe
authors.initials: MP
authors.lastname: Lafontaine
authors.affiliation: CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada; École de Technologie Supérieure, Département de Génie Électrique, Montreal, QC H3C 1K3, Canada.
authors.forename: Karine
authors.initials: K
authors.lastname: Lacourse
authors.affiliation: École de Technologie Supérieure, Département de Génie Électrique, Montreal, QC H3C 1K3, Canada; Centre de Recherches Mathématiques, Montreal, QC H3T 1J4, Canada.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Lina
authors.affiliation: Rotman Research Institute, Baycrest Center, Toronto, Ontario M6A 2E1, Canada; University of Toronto, Department of Psychology, Ontario M5S 3G3, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: McIntosh
authors.affiliation: Université de Montréal, Département de psychologie, Montreal, QC H3C 3J7, Canada.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gosselin
authors.affiliation: Université de Montréal, Département de psychologie, Montreal, QC H3C 3J7, Canada; CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada.
authors.forename: Hugo
authors.initials: H
authors.lastname: Théoret
authors.affiliation: Université de Montréal, Département de psychologie, Montreal, QC H3C 3J7, Canada; CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lippé
mesh_terms: D000328:Adult; D003627:Data Interpretation, Statistical; D004569:Electroencephalography / Q000379:methods; D000066499:Facial Recognition / Q000502:physiology*; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology*; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D021641:Recognition, Psychology / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013702:Temporal Lobe / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation; D055815:Young Adult
keywords: EEG; learning; multiscale entropy; prefrontal cortex; repetition suppression; tDCS