Purpose: Repetitive transcranial magnetic stimulation (rTMS) has attracted attention as a putative clinical neuromodulatory tool, including for ameliorating hallucinations, although existing clinical data are inconsistent. There is a notable paucity of research on its physiological effects on normal neuronal functioning.
Methods: We neuroimaged 24 healthy adult volunteers undertaking a variable loading passive auditory task, randomized into 2 matched and double-masked groups: half received a 17-minute 1 Hz right temporoparietal rTMS paradigm and half sham rTMS.
Results: One hertz rTMS led to attenuation of the underlying auditory cortex response to the stimulus and a contralateral increase in cortical activity. Subanalysis of the auditory tasks demonstrated that rTMS effects varied with stimulus frequency and differences between the active and sham conditions were lost at the highest frequency.
Conclusions: This work is, to the best of our knowledge, the first to neuroimage the effects of a "hallucinatory rTMS protocol" on basic auditory processing in healthy controls. Our data demonstrated that a so-called "inhibitory paradigm" can also produce distal neuronal activation and that effects can vary with neural loading. These results highlight the insufficient knowledge of the effects of rTMS on normal physiology, and this, combined with a lack of consensus on clinical trial parameters, may be contributing to the ambivalent data in therapeutic trials.