Transcranial Direct Current Stimulation Does Not Increase Auditory False Perceptions in Healthy Participants

We aimed to test a neurocognitive model positing that auditory hallucinations arise from a hyperactive left temporoparietal cortex and a hypoactive left dorsolateral prefrontal cortex. Specifically, 104 healthy individuals completed a signal detection task that induces auditory false perceptions while receiving transcranial direct current stimulation (tDCS). All participants were tested twice, once with real and once with sham tDCS. However, in half of the participants, the electrode montage mimicked the hypertemporal/hypofrontal model (anode over temporoparietal cortex and cathode over dorsolateral prefrontal cortex). In the other half, electrodes were reversed as in treatments of auditory verbal hallucinations. We hypothesized that these montages would lead to increased and decreased rates of auditory false perceptions, respectively. Moreover, we expected that auditory false perceptions would be triggered more often when participants expected certain words (top-down effect) and when these words were masked by human noise (bottom-up effect). The results revealed robust top-down and bottom-up interactions, but they were neither modulated by electrode montage nor by whether real or sham tDCS was administered. The results thus support the notion that auditory verbal hallucinations arise from an interaction of bottom-up and top-down processes but do not support the hypertemporal/hypofrontal model. Possible explanations for the lack of tDCS effects are discussed, including the idea that the tDCS electrodes might not have stimulated the targeted areas.