Abstract
Given the polarity dependent effects of transcranial direct current stimulation (tDCS) in facilitating or inhibiting neuronal processing, and tDCS effects on pitch perception, we tested the effects of tDCS on temporal aspects of auditory processing. We aimed to change baseline activity of the auditory cortex using tDCS as to modulate temporal aspects of auditory processing in healthy subjects without hearing impairment. Eleven subjects received 2mA bilateral anodal, cathodal and sham tDCS over auditory cortex in a randomized and counterbalanced order. Subjects were evaluated by the Random Gap Detection Test (RGDT), a test measuring temporal processing abilities in the auditory domain, before and during the stimulation. Statistical analysis revealed a significant interaction effect of time vs. tDCS condition for 4000 Hz and for clicks. Post-hoc tests showed significant differences according to stimulation polarity on RGDT performance: anodal improved 22.5% and cathodal decreased 54.5% subjects' performance, as compared to baseline. For clicks, anodal also increased performance in 29.4% when compared to baseline. tDCS presented polarity-dependent effects on the activity of the auditory cortex, which results in a positive or negative impact in a temporal resolution task performance. These results encourage further studies exploring tDCS in central auditory processing disorders.
Highlights
The processing of auditory information, an essential component of language, involves a complex neural network [1,2] composed of auditory pathway structures such as the cochlear nuclei, lateral lemniscus, inferior colliculus, medial geniculate nucleus and superior temporal gyrus
Based on the polarity dependent effect of transcranial direct current stimulation (tDCS) on neuronal spontaneous firing in which anodal stimulation leads to cellular membrane depolarization and cathodal to hyperpolarization [11], our hypothesis was that anodal stimulation would increase performance on Random Gap Detection Test (RGDT) and, cathodal stimulation would decrease RGDT performance
The main finding of this study was the observed effect of tDCS over auditory cortex in a test of central auditory processing
Summary
The processing of auditory information, an essential component of language, involves a complex neural network [1,2] composed of auditory pathway structures such as the cochlear nuclei, lateral lemniscus, inferior colliculus, medial geniculate nucleus and superior temporal gyrus. Failure or interference in the cortical processing of auditory information will affect the integration, understanding and, interpretation of sound stimuli In this sense, several studies have investigated the negative impact of changes in the central auditory processing in patients with neurological disorders [4,5], children with learning disabilities [6,7,8], and normal aging [9] that result in deficits on speech perception. Several studies have investigated the negative impact of changes in the central auditory processing in patients with neurological disorders [4,5], children with learning disabilities [6,7,8], and normal aging [9] that result in deficits on speech perception In this scenario, non-invasive alternatives to modulate specific central auditory functions that may promote gains in sound processing and speech perception are desirable
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