Changed categorical perception of consonant–vowel syllables induced by transcranial direct current stimulation (tDCS)

Kai Heimrath, Anna Fischer, Hans-Jochen Heinze, Tino Zaehle

Speech-related disorders may refer to impairment of temporal analysis in the human auditory system. By the advance of non-invasive brain stimulation new forms of therapy arise. In the present study, we examined the neuromodulatory effect of auditory tDCS on the perception of temporal modulated speech syllables. In three experimental sessions we assessed phonetic categorization of consonant-vowels (CV)-syllables (/da/,/ta/) with varying voice onset times (VOT) during sham, anodal, and cathodal tDCS delivered bilateral to the auditory cortex (AC). Subsequently, we recorded auditory evoked potentials (AEP) in response to voiced (/ba/,/da/,/ga/) and voiceless (/pa/,/ta/,/ka/) CV-syllables. In result, we demonstrate that bilateral tDCS of the AC can modulate CV-syllable perception. Behaviorally, cathodal tDCS improved phonetic categorization abilities in a VOT continuum accompanied by an elevation of the P50 amplitude of the AEP to CV-syllables during the anodal tDCS after effect. The present study demonstrates the ability of bilateral tDCS over the AC to ameliorate speech perception. The results may have clinical implications by fostering potential approaches for a treatment of speech-related pathologies with a deficit of temporal processing.