title: Low Intensity TMS Enhances Perception of Visual Stimuli.
abstract: BACKGROUND
  Transcranial magnetic stimulation (TMS) is a popular functional mapping tool in cognitive and sensory neuroscience. While strong TMS typically degrades performance, two recent studies have demonstrated that weak TMS, delivered to visual cortex, can improve performance on simple visual tasks. The improvement was interpreted as the summation of visually-evoked and TMS-elicited neuronal activity in visual cortex, but the nature of this interaction remains unclear.
  
  
  OBJECTIVE
  The present experiments sought to determine whether these weak pulses of TMS assist subjects to see the visual stimulus itself or create a distinct "melded" percept that may not be recognizable as the visual stimulus.
  
  
  METHODS
  We measured contrast thresholds in an orientation discrimination task in which participants reported the orientation (left or right) of gratings tilted 45° from vertical.
  
  
  RESULTS
  Weak TMS improved sensitivity for identifying gratings, suggesting that TMS sums with but preserves orientation information so that the subject can recognize the visual stimulus. We explain the effect using a mechanism of non-linear transduction of sensory signals in the brain.
  
  
  CONCLUSIONS
  The capability of low-intensity TMS to augment the neural signal while preserving information encoded in the stimulus can be employed as a novel approach to study the neural correlates of consciousness by selectively "pushing" an unconscious stimulus into consciousness.
authors.affiliation: School of Psychology, University of Sydney, Australia; Lab for Human Systems Neuroscience, RIKEN Brain Science Institute, Japan. Electronic address: arman@brain.riken.jp.
authors.forename: Arman
authors.initials: A
authors.lastname: Abrahamyan
authors.affiliation: School of Psychology, University of Sydney, Australia; School of Psychology, University of New South Wales, Australia.
authors.forename: Colin W G
authors.initials: CW
authors.lastname: Clifford
authors.affiliation: School of Psychology, University of Sydney, Australia; Eccles Institute of Neuroscience, The John Curtin School of Medical Research, Australian National University, Australia.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Arabzadeh
authors.affiliation: School of Psychology, University of Sydney, Australia.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Harris
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009949:Orientation / Q000502:physiology; D010775:Photic Stimulation; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Consciousness; Contrast detection; Orientation discrimination; Pedestal effect; Transcranial magnetic stimulation (TMS); Visual perception