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This Article Full Text Full Text (PDF) Supplemental Tables All Versions of this Article: 102/4/2303    most recent 00437.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Bergmann, T. O. Articles by Siebner, H. R. PubMed PubMed Citation Articles by Bergmann, T. O. Articles by Siebner, H. R.

RESEARCH-ARTICLE

Acute Changes in Motor Cortical Excitability During Slow Oscillatory and Constant Anodal Transcranial Direct Current Stimulation

¹Department of Neurology, Christian-Albrechts University of Kiel; ²Department of Neuroendocrinology, University of Lübeck, Lübeck, Germany; and ³Danish Research Center for Magnetic Resonance, Department of Magnetic Resonance, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark

Submitted 20 May 2009; accepted in final form 14 August 2009

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.