Neuronavigated TMS of early visual cortex eliminates unconscious processing of chromatic stimuli

Mikko Hurme; Mika Koivisto; Linda Henriksson; Henry Railo

doi:10.1016/j.neuropsychologia.2019.107266

Neuronavigated TMS of early visual cortex eliminates unconscious processing of chromatic stimuli

Neuropsychologia. 2020 Jan:136:107266. doi: 10.1016/j.neuropsychologia.2019.107266. Epub 2019 Nov 21.

Authors

Mikko Hurme¹, Mika Koivisto², Linda Henriksson³, Henry Railo⁴

Affiliations

¹ Department of Psychology, University of Turku, 20014, Finland; Turku Brain and Mind Centre, University of Turku, 20014, Finland. Electronic address: mijhur@utu.fi.
² Department of Psychology, University of Turku, 20014, Finland; Turku Brain and Mind Centre, University of Turku, 20014, Finland.
³ Department of Neuroscience and Biomedical Engineering, Aalto University, 02150, Finland.
⁴ Department of Psychology, University of Turku, 20014, Finland; Turku Brain and Mind Centre, University of Turku, 20014, Finland; Department of Clinical Neurophysiology, University of Turku and Turku University Hospital, 20521, Finland.

PMID: 31758972
DOI: 10.1016/j.neuropsychologia.2019.107266

Abstract

Some neurological patients with primary visual cortex (V1) lesions can guide their behavior based on stimuli presented to their blind visual field. One example of this phenomenon is the ability to discriminate colors in the absence of awareness. These so-called patients with blindsight must have a neural pathway that bypasses V1, explaining their ability to unconsciously process stimuli. The pathways that have been most often hypothesized to be the cause of blindsight connect lateral geniculate nucleus (LGN) or superior colliculus (SC) to extrastriate cortex, most likely V5, and parietal areas. To test if similar pathways function in neurologically healthy individuals or if unconscious processing depends on early visual cortex, we disturbed the visibility of a chromatic stimulus with metacontrast masking (Experiment 1) or neuronavigated transcranial magnetic stimulation (TMS) of early visual cortex, exact target being retinotopically mapped V1 (Experiment 2). We measured unconscious processing using the redundant target effect (RTE), which is the speeding up of reaction times in response to dual stimuli compared with one stimulus, when the task is to respond to any number of stimuli. An unconscious chromatic RTE was found when the visibility of the redundant chromatic stimulus was suppressed with a visual mask. When TMS was targeted to the correct retinotopic location of V1, and conscious perception of the redundant chromatic stimulus suppressed, the RTE was eliminated. Whether the elimination of unconscious RTE during TMS was exclusively due to disruption of V1 activity, or whether it was due to the possible interference with processing in V2 or even V3, is discussed. Based on our results and converging evidence from previous studies, we conclude that unconscious processing of chromatic information depends on the early visual cortex, in neurologically healthy participants.

Keywords: Blindsight; Color perception; Early visual cortex; Redundant target effect; TMS; Unconscious vision; V1.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Color Perception / physiology*
Female
Humans
Male
Neuronavigation
Perceptual Masking / physiology*
Transcranial Magnetic Stimulation*
Unconscious, Psychology*
Visual Cortex / physiology*
Young Adult