Single-pulse TMS |
Resting motor threshold and active motor threshold | Minimum TMS intensity to elicit an MEP with (usually) 50 μV peak-to-peak amplitude in the target muscle, either at rest (RMT) or during voluntary contraction (AMT) | Voltage-gated, sodium-channel-mediated neuronal membrane excitability | Increased by voltage-gated sodium channel blockers (e.g., carbamazepine, phenytoin and lamotrigine); decreased by ketamine | Lang et al. (61) (2013) Menzler et al. (62) (2014) Ziemann et al. (63) (1996) |
Amplitude of motor evoked potentials | Evoked by stimulus intensity above the motor threshold | Trans-synaptic activation of corticospinal neurons regulated by glutamatergic, GABAergic and neuromodulating neurotransmitters | Increased by ketamine, noradrenaline agonists (e.g., methylphenidate) and 5-HT agonists (e.g., sertraline); decreased by positive allosteric modulators of GABA receptors (e.g., lorazepam) | Ilic et al. (64) (2003) Gerdelat-Mas et al. (65) (2005) Paulus et al. (66) (2008) Boroojerdi et al. (30) (2001) Di Lazzaro et al. (67) (2000) |
Duration of cortical silent period | Duration of TMS-induced interruption in voluntary EMG activity of the target muscle | Motor cortical inhibition mediated by activation of GABA-A receptors (short CSPs) or GABA-B receptors (long CSPs) | Increased by benzodiazepines (short CSPs) and baclofen (specific GABA-B receptor agonist) | Inghilleri et al. (68) (1996) Siebner et al. (69) (1998) |
Short-latency afferent inhibition | Conditioning afferent electrical stimulus to the median or ulnar nerve at the wrist precedes TMS of the contralateral motor cortex by roughly 20 ms | Physiologic marker of the integrity and excitability of central cholinergic pathways | Increased by acetylcholinesterase inhibitors and nicotine; decreased by scopolamine (acetylcholine antagonist) and lorazepam (benzodiazepine) | Di Lazzaro et al. (70) (2005) Di Lazzaro et al. (71) (2005) Di Lazzaro et al. (67) (2000) |
Transcallosal inhibition | Single TMS pulses over the motor cortex ipsilateral to the voluntarily contracted hand muscle to induce a silent period in EMG activity | Duration of the silent period is thought to reflect the functioning of the corpus callosum and an inhibitory system in the contralateral motor cortex | | Ferbert et al. (34) (1992) Meyer et al. (72) (1998) |
Paired-pulse TMS |
Short-interval intracortical inhibition | Subthreshold conditioning stimulus precedes suprathreshold test stimulus by 1~5 ms | Short-lasting inhibition in regional corticospinal neurons mediated by GABA-A receptors containing α2 or α3 subunits | Increased by benzodiazepines (positive modulators at α1, α2, α3 or α5 subunits of GABA-A receptors); not affected by zolpidem (specific positive modulator of α1-GABA-A receptor) or S44819 (selective antagonist of α5-GABA-A receptor) | Di Lazzaro et al. (73) (2007) Di Lazzaro et al. (74) (2006) |
Intracortical facilitation | Subthreshold conditioning stimulus precedes suprathreshold test stimulus by 7~20 ms | Net excitation of an excitatory motor cortical network | Increased by noradrenergic agonists; decreased by NMDA receptor antagonists and benzodiazepines | Ziemann et al. (32) (1998) Ziemann et al. (75) (1996) Boroojerdi et al. (30) (2001) |
Long-interval intracortical inhibition | Two suprathreshold conditioning and test stimuli separated by 50~200 ms | GABA-B receptor–mediated slow inhibitory postsynaptic potentials | Increased by baclofen, tiagabine and vigabatrin | Pierantozzi et al. (76) (2004) Werhahn et al. (77) (1999) McDonnell et al. (29) (2006) |