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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

Electrodes montage for the High Definition transcranial direct current stimulation (HD-tDCS) experiment. (A) the gray point represents the central electrode, placed over PO8; the black points represent the other four (return) electrodes, placed over P4, OZ, TP8 and PO10. (B) Easycap, with electrodes placed according to the selected montage.
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Figure 3: Electrodes montage for the High Definition transcranial direct current stimulation (HD-tDCS) experiment. (A) the gray point represents the central electrode, placed over PO8; the black points represent the other four (return) electrodes, placed over P4, OZ, TP8 and PO10. (B) Easycap, with electrodes placed according to the selected montage.

Mentions: The selected target region for the stimulation was V5. HD-tDCS was administered using a battery-driven, constant-current generator (DC-Stimulator MC, neuroConn GmbH, Germany), connected to a passive HD-tDCS distributor (Soterix Medical, NY, USA). The optimal electrodes montage was selected by means of a bioelectromagnetic simulator of the current flow into the brain (Soterix HD-Explore, Soterix Medical, NY, USA). This software uses a finite element method to compute the distribution of the electrical field into a standard adult male head model, once the location of the electrodes and the stimulation parameters are given. Optimization criteria for the software were high focality and high field intensity in the target area. According to the solution of the optimization problem, the following montage was selected: the HD-tDCS cathode casing (Minhas et al., 2010) was placed in PO8 and four anode casings were placed at a distance of about 5 cm from the cathode, their location corresponding to P4, OZ, TP8, and PO10 according to the 10–10 standard EEG system (Figure 3). With this montage, the central electrode is right above V5 (Dumoulin et al., 2000). In order to increase conductivity, the hair under the casings was separated to expose the scalp skin, and about 3 ml of Signa Gel (Parker Laboratories, NJ, USA) were injected into the electrode casings. The electrodes were then placed into the gel solution inside the casings, and held in place with the casing cap (Easycap GmbH, Germany) (Borckardt et al., 2012). Impedance values were examined for each of the 5 electrodes and were all verified to be < 6 kΩ for the duration of the entire session. For real HD-tDCS, the current was ramped up to 2 mA (ramp duration of 30 s and maintained for 20 min. For sham HD-tDCS, the current was ramped up to 2 mA (ramp duration of 30 s and, after 1 min of full stimulation, it was ramped down to 0 mA (ramp duration of 30 s, and stayed off until the end of the session. This helped to mask sham and real conditions and gave to the participants a few seconds to adapt to the tickling sensation of the current.


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)

Electrodes montage for the High Definition transcranial direct current stimulation (HD-tDCS) experiment. (A) the gray point represents the central electrode, placed over PO8; the black points represent the other four (return) electrodes, placed over P4, OZ, TP8 and PO10. (B) Easycap, with electrodes placed according to the selected montage.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: Electrodes montage for the High Definition transcranial direct current stimulation (HD-tDCS) experiment. (A) the gray point represents the central electrode, placed over PO8; the black points represent the other four (return) electrodes, placed over P4, OZ, TP8 and PO10. (B) Easycap, with electrodes placed according to the selected montage.
Mentions: The selected target region for the stimulation was V5. HD-tDCS was administered using a battery-driven, constant-current generator (DC-Stimulator MC, neuroConn GmbH, Germany), connected to a passive HD-tDCS distributor (Soterix Medical, NY, USA). The optimal electrodes montage was selected by means of a bioelectromagnetic simulator of the current flow into the brain (Soterix HD-Explore, Soterix Medical, NY, USA). This software uses a finite element method to compute the distribution of the electrical field into a standard adult male head model, once the location of the electrodes and the stimulation parameters are given. Optimization criteria for the software were high focality and high field intensity in the target area. According to the solution of the optimization problem, the following montage was selected: the HD-tDCS cathode casing (Minhas et al., 2010) was placed in PO8 and four anode casings were placed at a distance of about 5 cm from the cathode, their location corresponding to P4, OZ, TP8, and PO10 according to the 10–10 standard EEG system (Figure 3). With this montage, the central electrode is right above V5 (Dumoulin et al., 2000). In order to increase conductivity, the hair under the casings was separated to expose the scalp skin, and about 3 ml of Signa Gel (Parker Laboratories, NJ, USA) were injected into the electrode casings. The electrodes were then placed into the gel solution inside the casings, and held in place with the casing cap (Easycap GmbH, Germany) (Borckardt et al., 2012). Impedance values were examined for each of the 5 electrodes and were all verified to be < 6 kΩ for the duration of the entire session. For real HD-tDCS, the current was ramped up to 2 mA (ramp duration of 30 s and maintained for 20 min. For sham HD-tDCS, the current was ramped up to 2 mA (ramp duration of 30 s and, after 1 min of full stimulation, it was ramped down to 0 mA (ramp duration of 30 s, and stayed off until the end of the session. This helped to mask sham and real conditions and gave to the participants a few seconds to adapt to the tickling sensation of the current.

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