title: A novel approach for documenting phosphenes induced by transcranial magnetic stimulation.
abstract: Stimulation of the human visual cortex produces a transient perception of light, known as a phosphene. Phosphenes are induced by invasive electrical stimulation of the occipital cortex, but also by non-invasive Transcranial Magnetic Stimulation (TMS)(1) of the same cortical regions. The intensity at which a phosphene is induced (phosphene threshold) is a well established measure of visual cortical excitability and is used to study cortico-cortical interactions, functional organization (2), susceptibility to pathology (3,4) and visual processing (5-7). Phosphenes are typically defined by three characteristics: they are observed in the visual hemifield contralateral to stimulation; they are induced when the subject s eyes are open or closed, and their spatial location changes with the direction of gaze (2). Various methods have been used to document phosphenes, but a standardized methodology is lacking. We demonstrate a reliable procedure to obtain phosphene threshold values and introduce a novel system for the documentation and analysis of phosphenes. We developed the Laser Tracking and Painting system (LTaP), a low cost, easily built and operated system that records the location and size of perceived phosphenes in real-time. The LTaP system provides a stable and customizable environment for quantification and analysis of phosphenes.
authors.affiliation: Department of Anatomy and Neurobiology, Boston University School of Medicine.
authors.forename: Seth
authors.initials: S
authors.lastname: Elkin-Frankston
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Fried
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.forename: R J
authors.initials: RJ
authors.lastname: Rushmore
authors.forename: Antoni
authors.initials: A
authors.lastname: Valero-Cabr
mesh_terms: D006801:Humans; D010719:Phosphenes / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*