Enhanced awareness followed reversible inhibition of human visual cortex: a combined TMS, MRS and MEG study

Allen, Christopher, Dunkley, Benjamin, Muthukumaraswamy, Suresh ORCID: https://orcid.org/0000-0001-7042-3920, Edden, Richard, Evans, Christopher John ORCID: https://orcid.org/0000-0002-6619-4245, Sumner, Petroc ORCID: https://orcid.org/0000-0002-0536-0510, Singh, Krishna ORCID: https://orcid.org/0000-0002-3094-2475 and Chambers, Christopher ORCID: https://orcid.org/0000-0001-6058-4114 2014. Enhanced awareness followed reversible inhibition of human visual cortex: a combined TMS, MRS and MEG study. PLoS ONE 9 (6) , e100350. 10.1371/journal.pone.0100350

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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 c-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 b 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-byinhibition in the visual cortex may provide a key foundation of consciousness.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Psychology
Subjects:	B Philosophy. Psychology. Religion > BF Psychology R Medicine > R Medicine (General)
Publisher:	Public Library of Science
ISSN:	1932-6203
Funders:	BBSRC, Wales Institute of Cognitive Neuroscience, Wellcome Trust, NIH
Date of First Compliant Deposit:	30 March 2016
Date of Acceptance:	23 May 2014
Last Modified:	05 Dec 2023 02:56
URI:	https://orca.cardiff.ac.uk/id/eprint/60955

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