Motor thresholds in humans: a transcranial magnetic stimulation study comparing different pulse waveforms, current directions and stimulator types

Modulation of somatosensory evoked potentials using transcranial magnetic intermittent theta burst stimulation

“…A similar effect of current orientation has been described on MEPs evoked by single biphasic pulses from M1 (Kammer et al, 2001) where anteromedially directed initial current has a slightly higher threshold and generates smaller MEPs than posterolateral current. Direct recordings of descending motor volleys evoked by the stimuli show that this is because different orientations of the stimulus evoke different combinations of I-wave volleys in the corticospinal tract (Di Lazzaro et al, 2001).…”

Inter-individual variability in optimal current direction for transcranial magnetic stimulation of the motor cortex

“…= 13.7 • ). A previous study with biphasic current that presents the motor threshold in individual participants finds that in all tested participants an initial current pulse in postero-lateral direction is more effective than the reverse orientation (Kammer et al, 2001). That study however evaluated only two directions -antero-medial and postero-lateral -and therefore any deviation of the optimal orientation from this axis would have gone undetected.…”

“…During biphasic stimulation the charge accumulation reaches its maximum amplitude during the second pulse (Corthout et al, 2001), and the maximal response is elicited when this second pulse is directed towards antero-medial, with the first pulse flowing postero-lateral (Kammer et al, 2001;Sommer et al, 2006).…”

Phosphene thresholds evoked with single and double TMS pulses

“…Similar to the motor cortex (e.g. Kammer et al, 2001a) biphasic pulses are more efficient compared to monophasic pulses. The replication of this observation in the visual cortex confirms a general neurophysiologic principle that holds for peripheral nerve preparations (Maccabee et al, 1998) as well as for cortical networks.…”