Abstract
Brain lesions in the visual associative cortex are known to impair visual perception, i.e., the capacity to correctly perceive different aspects of the visual world, such as motion, color, or shapes. Visual perception can be influenced by non-invasive brain stimulation such as transcranial direct current stimulation (tDCS). In a recently developed technique called high definition (HD) tDCS, small HD-electrodes are used instead of the sponge electrodes in the conventional approach. This is believed to achieve high focality and precision over the target area. In this paper we tested the effects of cathodal and anodal HD-tDCS over the right V5 on motion and shape perception in a single blind, within-subject, sham controlled, cross-over trial. The purpose of the study was to prove the high focality of the stimulation only over the target area. Twenty one healthy volunteers received 20 min of 2 mA cathodal, anodal and sham stimulation over the right V5 and their performance on a visual test was recorded. The results showed significant improvement in motion perception in the left hemifield after cathodal HD-tDCS, but not in shape perception. Sham and anodal HD-tDCS did not affect performance. The specific effect of influencing performance of visual tasks by modulating the excitability of the neurons in the visual cortex might be explained by the complexity of perceptual information needed for the tasks. This provokes a “noisy” activation state of the encoding neuronal patterns. We speculate that in this case cathodal HD-tDCS may focus the correct perception by decreasing global excitation and thus diminishing the “noise” below threshold.
Highlights
The visual cortex is the region of the brain responsible for visual perception
A typical montage for High Definition Transcranial direct current stimulation (tDCS) (HD-tDCS) is the 4 × 1 ring configuration, in which a central electrode is placed over the target region, and four return electrodes are placed around it in a ring-shape configuration (Datta et al, 2009)
We investigated the influence of high definition (HD)-tDCS on motion and shape perception
Summary
The visual cortex is the region of the brain responsible for visual perception. It is divided into the primary visual cortex V1, anatomically equivalent to Brodmann Area (BA) 17, and the extrastriate visual cortical areas V2, V3, V4, and V5, corresponding to BA 18 and 19 (Engel et al, 1997; Van den Stock et al, 2014).Abbreviations:HD-tDCS, High Definition transcranial direct current stimulation; BA, Brodmann Area; MT, Middle temporal area; MST, Medial superior temporal area; VA, Visual angle; VH, Visual hemifield; TAP, Test of Attentional Performance.HD-tDCS and visual motion perceptionThese visual areas are organized into two hierarchically and functionally specialized processing pathways: a ventral ‘‘what’’ stream, including V1, V2, V4 and the inferior temporal areas TEO and TE, for object vision; and a dorsal ‘‘where’’ stream, including V1, V2, V3, the middle temporal area (V5-MT), the medial superior temporal area (MST), and further stations in the inferior parietal and superior temporal sulcal cortex, for spatial vision and motion perception (Ungerleider and Haxby, 1994; Huberle et al, 2012).Visual perception can be influenced by non-invasive brain stimulation. Accornero et al studied the tDCS-induced modifications in visual evoked potentials (VEPP100) in humans, and found that anodal polarization reduced VEP-P100 amplitude whereas cathodal polarization significantly increased amplitude (Accornero et al, 2007). This suggests that, according to the polarity of the stimulation, anodal and cathodal tDCS elicits different effects. For instance, showed that conventional cathodal tDCS over the left V5 affected a visuomotor task by modifying only visual perception, and controlled it by stimulating different areas of the visual and motor cortex; anodal tDCS did not affect behavior. Behavioral performance on a visual motion task after stimulation of the right V5 needs to be further explored
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