title: Subjective characteristics of TMS-induced phosphenes originating in human V1 and V2.
abstract: One way to study the neural correlates of visual consciousness is to localize the cortical areas whose stimulation generates subjective visual sensations, called phosphenes. While there is support for the view that the stimulation of several different visual areas in the occipital lobe may produce phosphenes, it is not clear what the contribution of each area is. Here, we studied the roles of the primary visual cortex (V1) and the adjacent area V2 in eliciting phosphenes by using functional magnetic resonance imaging-guided transcranial magnetic stimulation (TMS) combined with spherical modeling of the TMS-induced electric field. Reports of the subjective visual features of phosphenes were systematically collected and analyzed. We found that selective stimulation of V1 and V2 are equally capable of generating phosphenes, as demonstrated by comparable phosphene thresholds and similar characteristics of phosphene shape, color, and texture. However, the phosphenes induced by V1 stimulation were systematically perceived as brighter than the phosphenes induced by the stimulation of V2. Thus, these results suggest that V1 and V2 have a similar capability to produce conscious percepts. Nevertheless, V1 and V2 contribute differently to brightness: neural activation originating in V1 generates a more intense sensation of brightness than similar activation originating in V2.
authors.affiliation: Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
authors.forename: Niina
authors.initials: N
authors.lastname: Salminen-Vaparanta
authors.affiliation: Advanced Magnetic Imaging Centre, Brain Research Unit, O.V. Lounasmaa Laboratory, Aalto University School of Science, Finland.
authors.forename: Simo
authors.initials: S
authors.lastname: Vanni
authors.affiliation: Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
authors.forename: Valdas
authors.initials: V
authors.lastname: Noreika
authors.affiliation: Department of Neurobiology and Biophysics, Vilnius University, Lithuania and.
authors.forename: Vladas
authors.initials: V
authors.lastname: Valiulis
authors.affiliation: Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland.
authors.forename: Levente
authors.initials: L
authors.lastname: Móró
authors.affiliation: Centre for Cognitive Neuroscience, Department of Psychology, University of Turku, Finland School of Humanities and Informatics, University of Skövde, Sweden.
authors.forename: Antti
authors.initials: A
authors.lastname: Revonsuo
mesh_terms: D000328:Adult; D001931:Brain Mapping; D003243:Consciousness / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010719:Phosphenes / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: V2; brightness; functional magnetic resonance imaging; primary visual cortex; transcranial magnetic stimulation