title: Enhanced awareness followed reversible inhibition of human visual cortex: a combined TMS, MRS and MEG study.
abstract: This series of experiments investigated the neural basis of conscious vision in humans using a form of transcranial magnetic stimulation (TMS) known as continuous theta burst stimulation (cTBS). Previous studies have shown that occipital TMS, when time-locked to the onset of visual stimuli, can induce a phenomenon analogous to blindsight in which conscious detection is impaired while the ability to discriminate 'unseen' stimuli is preserved above chance. Here we sought to reproduce this phenomenon using offline occipital cTBS, which has been shown to induce an inhibitory cortical aftereffect lasting 45-60 minutes. Contrary to expectations, our first experiment revealed the opposite effect: cTBS enhanced conscious vision relative to a sham control. We then sought to replicate this cTBS-induced potentiation of consciousness in conjunction with magnetoencephalography (MEG) and undertook additional experiments to assess its relationship to visual cortical excitability and levels of the inhibitory neurotransmitter γ-aminobutyric acid (GABA; via magnetic resonance spectroscopy, MRS). Occipital cTBS decreased cortical excitability and increased regional GABA concentration. No significant effects of cTBS on MEG measures were observed, although the results provided weak evidence for potentiation of event related desynchronisation in the β band. Collectively these experiments suggest that, through the suppression of noise, cTBS can increase the signal-to-noise ratio of neural activity underlying conscious vision. We speculate that gating-by-inhibition in the visual cortex may provide a key foundation of consciousness.
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: Christopher P G
authors: CP
authors: Allen
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom; The Hospital for Sick Children, Toronto, Ontario, Canada.
authors: Benjamin T
authors: BT
authors: Dunkley
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: Suresh D
authors: SD
authors: Muthukumaraswamy
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom; School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America.
authors: Richard
authors: R
authors: Edden
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: C John
authors: CJ
authors: Evans
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: Petroc
authors: P
authors: Sumner
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: Krish D
authors: KD
authors: Singh
authors: Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom.
authors: Christopher D
authors: CD
authors: Chambers
mesh_terms: D000328:Adult; D001364:Awareness; D003243:Consciousness / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011597:Psychomotor Performance; D011930:Reaction Time / Q000502:physiology; D059629:Signal-To-Noise Ratio; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D005680:gamma-Aminobutyric Acid