title: The causal role of the lateral occipital complex in visual mirror symmetry detection and grouping: an fMRI-guided TMS study.
abstract: Despite the fact that bilateral mirror symmetry is an important characteristic of the visual world, few studies have investigated its neural basis. Here we addressed this issue by investigating whether the object-selective lateral occipital (LO) cortex, a key brain region in object and shape processing, is causally involved in bilateral symmetry detection. Participants were asked to discriminate between symmetric and asymmetric dot patterns, while fMRI-guided repetitive TMS was delivered online over either the left LO, the right LO or two control sites in the occipital cortex. We found that the application of TMS over both right and left LO impaired symmetry judgments, with disruption being greater following right LO than left LO TMS, indicative of right hemisphere lateralization in symmetry processing. TMS over LO bilaterally also affected a visual contour detection task, with no evidence for hemispheric difference in this task. Overall, our results demonstrates that LO bilaterally plays a causal role in symmetry detection possibly due to symmetry acting as a strong cue in Gestalt processes mediating object recognition.
authors.affiliation: Brain Research Unit, OV Lounasmaa Laboratory, Aalto University School of Science, Espoo, Finland; BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Central Hospital, Helsinki, Finland; Advanced Magnetic Imaging Centre, Aalto Neuroimaging, OV Lounasmaa Laboratory, School of Science, Aalto University, Espoo, Finland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Bona
authors.affiliation: Department of Psychology, Rochester Institute of Technology, Rochester, NY, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Herbert
authors.affiliation: Department of Psychology, University of Milano, Milano, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Toneatto
authors.affiliation: Brain Research Unit, OV Lounasmaa Laboratory, Aalto University School of Science, Espoo, Finland; Department of Psychology, Faculty of Science and Technology, University of Westminster, UK.
authors.forename: Juha
authors.initials: J
authors.lastname: Silvanto
authors.affiliation: Department of Psychology, University of Milano, Milano, Italy; Brain Connectivity Center, IRCCS Mondino, Pavia, Italy. Electronic address: zaira.cattaneo@unimib.it.
authors.forename: Zaira
authors.initials: Z
authors.lastname: Cattaneo
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Bilateral mirror symmetry; LO; Lateralization; Shape detection; Symmetry detection; TMS; Visual cortex