Abstract
The aim of the present study was to test whether transcranial electrical stimulation can modulate illusory perception in the auditory domain. In two separate experiments we applied transcranial Direct Current Stimulation (anodal/cathodal tDCS, 2 mA; N = 60) and high-frequency transcranial Random Noise Stimulation (hf-tRNS, 1.5 mA, offset 0; N = 45) on the temporal cortex during the presentation of the stimuli eliciting the Deutsch's illusion. The illusion arises when two sine tones spaced one octave apart (400 and 800 Hz) are presented dichotically in alternation, one in the left and the other in the right ear, so that when the right ear receives the high tone, the left ear receives the low tone, and vice versa. The majority of the population perceives one high-pitched tone in one ear alternating with one low-pitched tone in the other ear. The results revealed that neither anodal nor cathodal tDCS applied over the left/right temporal cortex modulated the perception of the illusion, whereas hf-tRNS applied bilaterally on the temporal cortex reduced the number of times the sequence of sounds is perceived as the Deutsch's illusion with respect to the sham control condition. The stimulation time before the beginning of the task (5 or 15 min) did not influence the perceptual outcome. In accordance with previous findings, we conclude that hf-tRNS can modulate auditory perception more efficiently than tDCS.
Highlights
The effects of transcranial Electrical Stimulation have been widely exploited in the last decade to investigate the causal relationship between cortical activity of specific brain areas and cognitive or perceptual tasks (e.g., Miniussi and Ruzzoli, 2013; Filmer et al, 2014)
The results of the second analysis revealed that only the main effect of Category of response was significant [F(1, 54) = 1409.73, p < 0.001, ηp2 = 0.96]: the percentage of illusory responses was higher than the percentage of non-illusory responses (ILL = 94.42% ± 1.54; NO-ILL = 5.58% ± 1.54)
We can speculate that this evidence indirectly shows the involvement of auditory cortex (AC) in the genesis of the illusion, and that this effect can be ascribed either to the enhancement of the temporal cortex excitability or to the interference due to transcranial random noise stimulation (tRNS)
Summary
The effects of transcranial Electrical Stimulation (tES) have been widely exploited in the last decade to investigate the causal relationship between cortical activity of specific brain areas and cognitive or perceptual tasks (e.g., Miniussi and Ruzzoli, 2013; Filmer et al, 2014). Transcranial direct current stimulation (tDCS) is a type of tES that modulates cortical excitability in a polarity-dependent manner. The current is direct and flows from an active to a reference electrode, inducing a polarization of cortical neurons at a subthreshold level (Miniussi et al, 2013). A different type of current tES Effects on the Deutsch’s Illusion release characterizes transcranial random noise stimulation (tRNS). It consists in the application of repetitive alternating current over the cortex at random frequencies (0.1–640 Hz). Through the application of tRNS at high frequency (100–640 Hz) and with an intensity equal to or >1 mA, it has been shown that the stimulation is able to positively modulate the excitability of motor and auditory areas (Moliadze et al, 2012; Van Doren et al, 2014) as well as to improve performance in behavioral tasks, for example in the domain of motor and visual perception learning (Terney et al, 2008; Fertonani et al, 2011)
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