Anodal transcranial direct current stimulation reduces collinear lateral inhibition in normal peripheral vision

Abstract

Collinear flanking stimuli can reduce the detectability of a Gabor target presented in peripheral vision. This phenomenon is called collinear lateral inhibition and it may contribute to crowding in peripheral vision. Perceptual learning can reduce collinear lateral inhibition in peripheral vision, however intensive training is required. Our aim was to assess whether modulation of collinear lateral inhibition can be achieved within a short time-frame using a single 20-minute session of primary visual cortex anodal transcranial direct current stimulation (a-tDCS). Thirteen observers with normal vision performed a 2AFC contrast detection task with collinear flankers positioned at a distance of 2λ from the target (lateral inhibition) or 6λ (control condition). The stimuli were presented 6˚to the left of a central cross and fixation was monitored with an infra-red eye tracker. Participants each completed two randomly sequenced, single-masked stimulation sessions; real anodal tDCS and sham tDCS. For the 2λ separation condition, a-tDCS induced a significant reduction in detection threshold (reduced lateral inhibition). Sham stimulation had no effect. No effects of a-tDCS were observed for the 6λ separation condition. This result lays the foundation for future work investigating whether a-tDCS may be useful as a visual rehabilitation tool for individuals with central vision loss who are reliant on peripheral vision.

Anodal Occipital Transcranial Direct Current Stimulation Enhances Perceived Visual Size Illusions

“…Visual size illusions have been found to be correlated with the functional and structural features of the primary visual cortex ( V1). Specifically, the spatial extent of V1 activity reflects the perceived size rather than the physical size of an object (Pooresmaeili, Arrighi, Biagi, & Morrone, 2013;Fang, Boyaci, Kersten, & Murray, 2008;Murray, Boyaci, & Kersten, 2006). Similar V1 activation patterns have been observed for an afterimage whose apparent size varies with distance (Sperandio, Chouinard, & Goodale, 2012).…”

Visual cortex cTBS increases mixed percept duration while a-tDCS has no effect on binocular rivalry

“…The most obvious explanation for the lack of an a-tDCS effect on mixed percept duration is that a-tDCS simply had no effect on the visual cortex at all. Although we certainly can't rule out this possibility, the vast majority of published studies using the same or similar stimulation parameters over visual cortex have reported a-tDCS effects, including effects that are consistent with reduced GABA-mediated inhibition such as reduced surround suppression (22), reduced lateral inhibition (23) and an equalization of the cortical response to each eye in adults with amblyopia (3,4). Therefore, we also propose a number of alternative explanations.…”

Reduction of collinear inhibition in observers with central vision loss using anodal transcranial direct current stimulation: A case series

“…A larger target/flanker separation of 6λ was also tested as an additional control condition. Larger target flanker separations induce collinear facilitation, the opposite to collinear inhibition [10,15]. Participants were encouraged to adopt their habitual head position so that they could see the fixation cross clearly.…”

“…In particular, anodal tDCS (a-tDCS) increases cortical excitability and reduces the concentration of the inhibitory neurotransmitter GABA [14]. Using a-tDCS over the visual cortex, we have recently demonstrated that collinear inhibition can be reduced in observers with normal vision [15]. Collinear inhibition (also called lateral masking) refers to the impaired detectability of a visual target when it is flanked by similarly oriented high contrast targets and is one of the low-level mechanisms involved in visual crowding [16].…”