Modulation of oscillatory activity in response to very low intensity transcranial magnetic stimulation in the human primary motor cortex

Transcranial Magnetic Stimulation (TMS) is widely used to probe and modulate human brain function, yet the neural effects of stimulation delivered at very low intensities remain unclear. Here, we show that very low intensity TMS can alter ongoing oscillatory activity in the human primary motor cortex. In healthy participants, we combined TMS with electroencephalography (EEG) and assessed neural responses to single pulses and rhythmic stimulation in the motor cortex.

Conventional high intensity stimulation produced robust local evoked responses and synchronized beta-frequency oscillations in the directly TMS-targeted cortical area. Low intensity rhythmic stimulation, despite not evoking measurable responses, modified local oscillatory activity in a manner consistent with phase-dependent enhancement of ongoing rhythms. These findings suggest that cortical oscillations can be influenced by magnetic fields substantially weaker than those typically employed to date in human studies.

Very low intensity stimulation may therefore offer a route towards portable, energy-efficient technologies for investigating and modulating brain networks. Mutanen for conceptual contributions and support with TMS-EEG data analyses, and Ms. Carlo Leto for assistance with data collection.

This work and contributions of X.C.-T. were mainly supported by the BrainMAG project funded by the Agence Nationale de la Recherche in France (ANR-19-CE37-0021) to A.V.-C. Additional support for MRI datasets and IRB coverage was provided by the Big Brain Theory (BBT-3; FORTE) ICM grant to Dr. Cécile Gallea, A.V.-C. and M.B.

The participation of M.B. was also supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement 897941. IHU-ICM CARNOT Maturation grant and additional funding came from Investissements d’avenir (ANR-10- IAIHU-0006) awarded to XC-T and AV-C for associated projects. Causal Dynamics, Plasticity and Rehabilitation Group, FRONTLAB team, Sorbonne Université, Institut du Cerveau – Paris Brain Institute – ICM, INSERM 1127, CNRS, 7225, APHP-Hôpital de la Pitié Salpêtrière, Paris, France Xavier Corominas-Teruel, Martina Bracco & Antoni Valero-Cabré Danish Research Centre for Magnetic Resonance, Department of Radiology and Nuclear Medicine, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark Department of Psychology and Research Center for Behaviour Assessment (CRAMC), Universitat Rovira i Virgili, Neurobehavior and Health Research Group, NEUROLAB, Tarragona, Spain MOV’IT team, Sorbonne Université, Institut du Cerveau – Paris Brain Institute – ICM, INSERM 1127, CNRS 7225, APHP-Hôpital de la Pitié Salpêtrière, Paris, France Development, Adaptation and Ageing, INSERM 1345 & CNRS8263, IBPS-Dev2A, Sorbonne Université, Paris, France ‘Network Dynamics and Cellular Excitability’ team, Sorbonne Université, Institut du Cerveau – Paris Brain Institute – ICM, INSERM, CNRS, APHP, Hôpital de la Pitié Salpêtrière, Paris, France Cognitive Neuroscience and Information Tech.

Research Program, Open University of Catalonia (UOC), Barcelona, Spain Severine Mahon, Stéphane Charpier & Antoni Valero-Cabré Dept. Anatomy and Neurobiology, Laboratory of Cerebral Dynamics, Boston University School of Medicine, Boston, MA, USA The authors declare no competing interests. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.