No Effects of Transcranial Direct Current Stimulation on Visual Evoked Potential and Peak Gamma Frequency
Evidence suggests that the visual evoked potential (VEP) and gamma oscillations elicited by visual stimuli reflect the balance of excitatory and inhibitory (E-I) cortical processes. As tDCS has been shown to modulate E–I balance, the current study investigated whether amplitudes of VEP components (N1 and P2) and peak gamma frequency are modulated by transcranial direct current stimulation (tDCS). Healthy adults underwent two electroencephalography (EEG) recordings while viewing stimuli designed to elicit a robust visual response. Between the two recordings, participants were randomly assigned to three tDCS conditions (anodal-, cathodal-, and sham- tDCS) or received no-tDCS. tDCS electrodes were placed over the occipital cortex (Oz) and the left cheek with an intensity of 2 mA for 10 min. Data of 39 participants were analysed for VEP amplitudes and peak gamma frequency using mixed-model ANOVAs. The results showed no main effects of tDCS in any metric. Possible explanations for the absence of tDCS effects are discussed.
Excitation-inhibition (E-I) balance has been indirectly inferred from psychophysical measures (i.e., performance in orientation discrimination task [ODT]) and neurophysiological measures (i.e.,…
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The discrepancy in the effectiveness of transcranial Direct Current Stimulation (tDCS) on cognitive processes raises the need for further investigations.