Improving the Transcranial Magnetic Stimulation Experience: How Transcranial Magnetic Stimulation Parameters and Coil Design Affect Somatosensory Sensations

OBJECTIVES: Transcranial magnetic stimulation (TMS) often elicits scalp sensations and muscle twitches. These sensory side effects can confound research outcomes and cause discomfort in clinical use, yet they remain poorly characterized. The goal of this study is to systematically characterize TMS-induced sensations and investigate (1) the effects of key TMS parameters (intensity, location, protocol, coil type), (2) whether a novel coil design reduces unpleasant sensations, and (3) whether an advanced sham coil can effectively mimic the sensory profile of active TMS. MATERIALS AND METHODS: Overall, 48 participants participated in two experiments. Scalp sensations were rated using a ten-dimensional questionnaire across stimulation sites (F3, Cz, P4), intensities (80%, 100%, and 120% of resting motor threshold), and protocols (1 Hz, 10 Hz, and intermittent theta burst stimulation), using different coil types (experiment I: novel vs overlapping; experiment II: novel vs standard vs sham). RESULTS: Scalp sensations were systematically influenced by stimulation intensity, position, and protocol, with consistent main effects across nearly all sensory dimensions and various interactions shedding light on the complex interplay of TMS parameters. Coil type significantly shaped the sensory profile: The novel coil reduced muscle twitches compared with the standard coil, and the sham coil closely replicated the sensory experience of active stimulation. CONCLUSIONS: This study provides a comprehensive characterization of TMS-induced sensations and highlights the significant effects of the TMS parameters and their interplay on scalp sensations. Novel coil designs offer promising options to reduce discomfort and improve sensory blinding, thereby minimizing confounding effects in both experimental and clinical TMS applications.