title: State-dependent effects of transcranial oscillatory currents on the motor system: what you think matters.
abstract: Imperceptible transcranial alternating current stimulation (tACS) changes the endogenous cortical oscillatory activity in a frequency-specific manner. In the human motor system, tACS coincident with the idling beta rhythm of the quiescent motor cortex increased the corticospinal output. We reasoned that changing the initial state of the brain (i.e., from quiescence to a motor imagery task that desynchronizes the local beta rhythm) might also change the susceptibility of the corticospinal system to resonance effects induced by beta-tACS. We tested this hypothesis by delivering tACS at different frequencies (theta, alpha, beta, and gamma) on the primary motor cortex at rest and during motor imagery. Motor-evoked potentials (MEPs) were obtained by transcranial magnetic stimulation (TMS) on the primary motor cortex with an online-navigated TMS-tACS setting. During motor imagery, the increase of corticospinal excitability was maximal with theta-tACS, likely reflecting a reinforcement of working memory processes required to mentally process and "execute" the cognitive task. As expected, the maximal MEPs increase with subjects at rest was instead obtained with beta-tACS, substantiating previous evidence. This dissociation provides new evidence of state and frequency dependency of tACS effects on the motor system and helps discern the functional role of different oscillatory frequencies of this brain region. These findings may be relevant for rehabilitative neuromodulatory interventions.
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Sezione di Neurologia e Neurofisiologia Clinica, Azienda Ospedaliera-Universitaria Senese, Policlinico Le Scotte, I-53100, Siena, Italy, Servizio di Statistica Medica e Tecnologie di Informazione, Associazione Fatebenefratelli per la Ricerca Biomedica e Salute, Centro San Benedetto Menni-Fatebenefratelli, I-00186, Roma, Italy, and Epidemiologia e Biostatistica, Casa di Cura "San Raffaele-Cassino", Tosinvest, I-03043, Cassino, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Feurra
authors.forename: Patrizio
authors.initials: P
authors.lastname: Pasqualetti
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bianco
authors.forename: Emiliano
authors.initials: E
authors.lastname: Santarnecchi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rossi
authors.forename: Simone
authors.initials: S
authors.lastname: Rossi
mesh_terms: D000328:Adult; D058256:Brain Waves / Q000502:physiology*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D011597:Psychomotor Performance / Q000502:physiology*; D013850:Thinking / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods