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Modulating parameters of excitability during and after transcranial direct current stimulation of the human motor cortex
Author(s) -
Nitsche Michael A.,
Seeber Antje,
Frommann Kai,
Klein Cornelia Carmen,
Rochford Christian,
Nitsche Maren S.,
Fricke Kristina,
Liebetanz David,
Lang Nicolas,
Antal Andrea,
Paulus Walter,
Tergau Frithjof
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.092429
Subject(s) - transcranial direct current stimulation , facilitation , neuroscience , motor cortex , stimulation , primary motor cortex , psychology , transcranial magnetic stimulation , neuroplasticity , brain stimulation
Weak transcranial direct current stimulation (tDCS) of the human motor cortex results in excitability shifts which occur during and after stimulation. These excitability shifts are polarity‐specific with anodal tDCS enhancing excitability, and cathodal reducing it. To explore the origin of this excitability modulation in more detail, we measured the input–output curve and motor thresholds as global parameters of cortico‐spinal excitability, and determined intracortical inhibition and facilitation, as well as facilitatory indirect wave (I‐wave) interactions. Measurements were performed during short‐term tDCS, which elicits no after‐effects, and during other tDCS protocols which do elicit short‐ and long‐lasting after‐effects. Resting and active motor thresholds remained stable during and after tDCS. The slope of the input–output curve was increased by anodal tDCS and decreased by cathodal tDCS. Anodal tDCS of the primary motor cortex reduced intracortical inhibition and enhanced facilitation after tDCS but not during tDCS. Cathodal tDCS reduced facilitation during, and additionally increased inhibition after its administration. During tDCS, I‐wave facilitation was not influenced but, for the after‐effects, anodal tDCS increased I‐wave facilitation, while cathodal tDCS had only minor effects. These results suggest that the effect of tDCS on cortico‐spinal excitability during a short period of stimulation (which does not induce after‐effects) primarily depends on subthreshold resting membrane potential changes, which are able to modulate the input‐output curve, but not motor thresholds. In contrast, the after‐effects of tDCS are due to shifts in intracortical inhibition and facilitation, and at least partly also to facilitatory I‐wave interaction, which is controlled by synaptic activity.