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Cathodal HD-tDCS on the right V5 improves motion perception in humans.

Zito GA, Senti T, Cazzoli D, Müri RM, Mosimann UP, Nyffeler T, Nef T - Front Behav Neurosci (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Gerontechnology and Rehabilitation Group, University of Bern Bern, Switzerland.

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.

No MeSH data available.


Related in: MedlinePlus

Visual tests setup, as it appeared to the subjects. (A) hemispherical screen used to perform the tests. (B) Speed Task. The arrows represent the speed of the dots, which, in this example, are faster in the left hemisphere. Here subjects are asked to decrease the speed of the dots on the left in order to make them as fast as the dots on the right. (C) Shape Task with two ellipses, the axes ratio of the ellipse in the left hemisphere is higher than the one in the right. Here subjects are asked to decrease the axes ratio of the ellipse on the left in order to make it identical to the ellipse on the right.
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Figure 2: Visual tests setup, as it appeared to the subjects. (A) hemispherical screen used to perform the tests. (B) Speed Task. The arrows represent the speed of the dots, which, in this example, are faster in the left hemisphere. Here subjects are asked to decrease the speed of the dots on the left in order to make them as fast as the dots on the right. (C) Shape Task with two ellipses, the axes ratio of the ellipse in the left hemisphere is higher than the one in the right. Here subjects are asked to decrease the axes ratio of the ellipse on the left in order to make it identical to the ellipse on the right.

Mentions: For the visual tests, subjects were seated with their head resting on a chin- and forehead rest at the center of a hemispherical screen (cupola, Figure 2A), where visual stimuli were projected, and held an input device with three buttons in their dominant hand; two buttons to manipulate the images and one to confirm the choice. The tests followed a balance paradigm, in which subjects had to compare two images presented on the left and the right half of the cupola, respectively, at an eccentricity of 7.6° visual angles (VA) from its center, while fixating a central marker point (0° VA eccentricity). In this setup, the two halves of the hemispherical screen corresponded to the two visual hemifields (VH). Two different subtasks, with 12 repetitions per task, were administered in a pseudo-random order. In the first one, called the Speed Task, two patterns of dots moving in random direction at two different speeds were presented. The subjects were asked to consider the speed of the dots on the right VH as reference, and to use the two buttons of the input device to change (increase or decrease) the speed of the dots on the left VH until they matched the reference (Figure 2B). Reference speeds were 0.36° VA/s, 1.07° VA/s, 1.80° VA/s, and 2.52° VA/s. In the second subtask, called the Shape Task, two ellipses with different ratios between the vertical and the horizontal axes, were presented. The subjects were asked to consider the ellipse on the right VH as reference, and to change the ratio of the ellipse on the left VH until it was perceived as identical as the one on the right VH (Figure 2C). Reference ratios were 0.3, 0.6, 1.5 and 1.8.


Cathodal HD-tDCS on the right V5 improves motion perception in humans.

Zito GA, Senti T, Cazzoli D, Müri RM, Mosimann UP, Nyffeler T, Nef T - Front Behav Neurosci (2015)

Visual tests setup, as it appeared to the subjects. (A) hemispherical screen used to perform the tests. (B) Speed Task. The arrows represent the speed of the dots, which, in this example, are faster in the left hemisphere. Here subjects are asked to decrease the speed of the dots on the left in order to make them as fast as the dots on the right. (C) Shape Task with two ellipses, the axes ratio of the ellipse in the left hemisphere is higher than the one in the right. Here subjects are asked to decrease the axes ratio of the ellipse on the left in order to make it identical to the ellipse on the right.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585077&req=5

Figure 2: Visual tests setup, as it appeared to the subjects. (A) hemispherical screen used to perform the tests. (B) Speed Task. The arrows represent the speed of the dots, which, in this example, are faster in the left hemisphere. Here subjects are asked to decrease the speed of the dots on the left in order to make them as fast as the dots on the right. (C) Shape Task with two ellipses, the axes ratio of the ellipse in the left hemisphere is higher than the one in the right. Here subjects are asked to decrease the axes ratio of the ellipse on the left in order to make it identical to the ellipse on the right.
Mentions: For the visual tests, subjects were seated with their head resting on a chin- and forehead rest at the center of a hemispherical screen (cupola, Figure 2A), where visual stimuli were projected, and held an input device with three buttons in their dominant hand; two buttons to manipulate the images and one to confirm the choice. The tests followed a balance paradigm, in which subjects had to compare two images presented on the left and the right half of the cupola, respectively, at an eccentricity of 7.6° visual angles (VA) from its center, while fixating a central marker point (0° VA eccentricity). In this setup, the two halves of the hemispherical screen corresponded to the two visual hemifields (VH). Two different subtasks, with 12 repetitions per task, were administered in a pseudo-random order. In the first one, called the Speed Task, two patterns of dots moving in random direction at two different speeds were presented. The subjects were asked to consider the speed of the dots on the right VH as reference, and to use the two buttons of the input device to change (increase or decrease) the speed of the dots on the left VH until they matched the reference (Figure 2B). Reference speeds were 0.36° VA/s, 1.07° VA/s, 1.80° VA/s, and 2.52° VA/s. In the second subtask, called the Shape Task, two ellipses with different ratios between the vertical and the horizontal axes, were presented. The subjects were asked to consider the ellipse on the right VH as reference, and to change the ratio of the ellipse on the left VH until it was perceived as identical as the one on the right VH (Figure 2C). Reference ratios were 0.3, 0.6, 1.5 and 1.8.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Gerontechnology and Rehabilitation Group, University of Bern Bern, Switzerland.

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.

No MeSH data available.


Related in: MedlinePlus