title: Acute changes in motor cortical excitability during slow oscillatory and constant anodal transcranial direct current stimulation.
abstract: Transcranial oscillatory current stimulation has recently emerged as a noninvasive technique that can interact with ongoing endogenous rhythms of the human brain. Yet, there is still little knowledge on how time-varied exogenous currents acutely modulate cortical excitability. In ten healthy individuals we used on-line single-pulse transcranial magnetic stimulation (TMS) to search for systematic shifts in corticospinal excitability during anodal sleeplike 0.8-Hz slow oscillatory transcranial direct current stimulation (so-tDCS). In separate sessions, we repeatedly applied 30-s trials (two blocks at 20 min) of either anodal so-tDCS or constant tDCS (c-tDCS) to the primary motor hand area during quiet wakefulness. Simultaneously and time-locked to different phase angles of the slow oscillation, motor-evoked potentials (MEPs) as an index of corticospinal excitability were obtained in the contralateral hand muscles 10, 20, and 30 s after the onset of tDCS. MEPs were also measured off-line before, between, and after both stimulation blocks to detect any lasting excitability shifts. Both tDCS modes increased MEP amplitudes during stimulation with an attenuation of the facilitatory effect toward the end of a 30-s tDCS trial. No phase-locking of corticospinal excitability to the exogenous oscillation was observed during so-tDCS. Off-line TMS revealed that both c-tDCS and so-tDCS resulted in a lasting excitability increase. The individual magnitude of MEP facilitation during the first tDCS trials predicted the lasting MEP facilitation found after tDCS. We conclude that sleep slow oscillation-like excitability changes cannot be actively imposed on the awake cortex with so-tDCS, but phase-independent on-line as well as off-line facilitation can reliably be induced.
authors.affiliation: Department of Neurology, Christian-Albrechts University Kiel, D-24105 Kiel, Germany. t.bergmann@neurologie.uni-kiel.de
authors.forename: Til Ole
authors.initials: TO
authors.lastname: Bergmann
authors.forename: Sergiu
authors.initials: S
authors.lastname: Groppa
authors.forename: Markus
authors.initials: M
authors.lastname: Seeger
authors.forename: Matthias
authors.initials: M
authors.lastname: Mölle
authors.forename: Lisa
authors.initials: L
authors.lastname: Marshall
authors.forename: Hartwig Roman
authors.initials: HR
authors.lastname: Siebner
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods*; D019054:Evoked Potentials, Motor; D006225:Hand; D006801:Humans; D016014:Linear Models; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D010507:Periodicity; D011712:Pyramidal Tracts / Q000502:physiology; D012890:Sleep; D011795:Surveys and Questionnaires; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D014851:Wakefulness; D055815:Young Adult