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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

Figure adapted from Antal et al. (2004). Example of the mechanism of interaction between tDCS and the cortical excitability. (A) in the Sham condition, many concurrent neuronal patterns, together with the optimal one, are simultaneously activated producing a “noisy” activation state. (B) in the Cathodal condition, the cortical excitability is globally decreased and the optimal pattern is the only one still above threshold, thus a focus effect is present. (C) in the Anodal condition, the global excitation of the concurrent patterns does not produce any change in the behavior because the “noise” is not filtered.
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Figure 6: Figure adapted from Antal et al. (2004). Example of the mechanism of interaction between tDCS and the cortical excitability. (A) in the Sham condition, many concurrent neuronal patterns, together with the optimal one, are simultaneously activated producing a “noisy” activation state. (B) in the Cathodal condition, the cortical excitability is globally decreased and the optimal pattern is the only one still above threshold, thus a focus effect is present. (C) in the Anodal condition, the global excitation of the concurrent patterns does not produce any change in the behavior because the “noise” is not filtered.

Mentions: A speculative explanation of such effects was found in the complexity of perceptual information needed for the tasks. When high resolution, temporo-spatial analysis, and comparison of motion speeds and directions are involved, different encoding neuronal patterns in response to the different speeds and motion directions may activate simultaneously. This probably results in a globally “noisy” activation state, where optimal and suboptimal patterns are both present at the same time (Figure 6A). Hypothesizing a threshold in the neuronal activation, above which a behavioral change can be observed, Antal et al. speculated that cathodal stimulation may focus the correct perception of these parameters by decreasing global activation level. As a consequence of this, the amount of activation of concurrent patterns is diminished below threshold (Figure 6B; Antal et al., 2006). Similar argumentations can be made for the results of the present study. In our Speed Task, for instance, speeds of dots moving in several random directions are compared. The random directions of the dots might tune different groups of neurons, and this might result in the “noisy” activation state addressed by Antal et al. Here the optimal neuronal patterns represent the target speeds, and the suboptimal patterns represent the different motion directions of the dots. It is plausible that, after cathodal HD-tDCS, the neuronal activation state looks like the one shown in Figure 6B, where only the optimal pattern is still above threshold. Anodal stimulation would, on the other hand, increase the neuronal activation even more but, since the mentioned concurrent patterns are already above threshold, no effect on the performance is observed (Figure 6C). This explanation is supported by studies in macaque monkeys, where it has been demonstrated that different neurons in V5 show a high selectivity for different motion speeds and directions (Maunsell and Van Essen, 1983; Albright, 1984; Duijnhouwer et al., 2013).


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)

Figure adapted from Antal et al. (2004). Example of the mechanism of interaction between tDCS and the cortical excitability. (A) in the Sham condition, many concurrent neuronal patterns, together with the optimal one, are simultaneously activated producing a “noisy” activation state. (B) in the Cathodal condition, the cortical excitability is globally decreased and the optimal pattern is the only one still above threshold, thus a focus effect is present. (C) in the Anodal condition, the global excitation of the concurrent patterns does not produce any change in the behavior because the “noise” is not filtered.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: Figure adapted from Antal et al. (2004). Example of the mechanism of interaction between tDCS and the cortical excitability. (A) in the Sham condition, many concurrent neuronal patterns, together with the optimal one, are simultaneously activated producing a “noisy” activation state. (B) in the Cathodal condition, the cortical excitability is globally decreased and the optimal pattern is the only one still above threshold, thus a focus effect is present. (C) in the Anodal condition, the global excitation of the concurrent patterns does not produce any change in the behavior because the “noise” is not filtered.
Mentions: A speculative explanation of such effects was found in the complexity of perceptual information needed for the tasks. When high resolution, temporo-spatial analysis, and comparison of motion speeds and directions are involved, different encoding neuronal patterns in response to the different speeds and motion directions may activate simultaneously. This probably results in a globally “noisy” activation state, where optimal and suboptimal patterns are both present at the same time (Figure 6A). Hypothesizing a threshold in the neuronal activation, above which a behavioral change can be observed, Antal et al. speculated that cathodal stimulation may focus the correct perception of these parameters by decreasing global activation level. As a consequence of this, the amount of activation of concurrent patterns is diminished below threshold (Figure 6B; Antal et al., 2006). Similar argumentations can be made for the results of the present study. In our Speed Task, for instance, speeds of dots moving in several random directions are compared. The random directions of the dots might tune different groups of neurons, and this might result in the “noisy” activation state addressed by Antal et al. Here the optimal neuronal patterns represent the target speeds, and the suboptimal patterns represent the different motion directions of the dots. It is plausible that, after cathodal HD-tDCS, the neuronal activation state looks like the one shown in Figure 6B, where only the optimal pattern is still above threshold. Anodal stimulation would, on the other hand, increase the neuronal activation even more but, since the mentioned concurrent patterns are already above threshold, no effect on the performance is observed (Figure 6C). This explanation is supported by studies in macaque monkeys, where it has been demonstrated that different neurons in V5 show a high selectivity for different motion speeds and directions (Maunsell and Van Essen, 1983; Albright, 1984; Duijnhouwer et al., 2013).

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