Abstract
Transcranial magnetic stimulation (TMS) is commonly employed for diagnostic and therapeutic purposes to enhance recovery following brain injury, such as stroke or intracerebral hemorrhage (ICH). Single-pulse TMS, most commonly used for diagnostic purposes and with motor evoked potential (MEP) recordings, is not suitable for clinical use in patients with severe motor paresis. To overcome this problem, we developed a quadripulse theta burst transcranial magnetic stimulation (QTS) device that combines the output from 16 stimulators to deliver a train of 16 monophasic magnetic pulses through a single coil. High-frequency theta rhythm magnetic bursts (bursts of four monophasic pulses, at 500 Hz, i.e., with a 2-ms interpulse interval, repeated at 5 Hz) were generated via a set of 16 separate magnetic stimulators connected to a specially designed combination module. No adverse effects or electroencephalogram (EEGs) abnormalities were identified during or after the recordings. MEP amplification in the QTS during four-burst theta rhythm stimulations produced four independent MEPs 20 ms after each burst onset maximizing the final third or fourth burst, which exhibited significantly greater amplitude than those resulting from a single burst or pulse. Motor functional palsy grades after ICH and QTS-MEP parameters and resting motor threshold (RMT) and amplitudes were significantly correlated (r = −0.83/−0.81 and 0.89/0.87; R2 = 0.69/0.66 and 0.79/0.76, p < 0.001; anterior/posterior-stimulus polarity, respectively). In conclusion, QTS-MEPs enabled a linear functional evaluation in patients with various degrees of motor paresis. However, the benefits, safety, and limitations of this device should be further explored in future studies.
Highlights
Transcranial magnetic stimulation (TMS) is commonly employed as an exploratory or diagnostic tool in neuroscience research and for various neurological disorders (Rothwell, 1997; MüllerDahlhaus and Vlachos, 2013)
Theta burst stimulation (TBS) of the human motor cortex, which was originally reported in experimental hippocampal studies for long-term potentiation/depression induction (Hess and Donoghue, 1996), has been successfully translated to awake humans
It has been demonstrated that anterior-posterior (AP) directed continuous quadripulse theta burst magnetic stimulation (QTS) at 666 Hz, with a burst repetition rate of 5 Hz, using 90% active motor threshold-TMS to the hand area of the primary motor cortex, induced an AP-motor evoked potential (MEP) amplitude increase lasting up to 60 min (Jung et al, 2016)
Summary
Transcranial magnetic stimulation (TMS) is commonly employed as an exploratory or diagnostic tool in neuroscience research and for various neurological disorders (Rothwell, 1997; MüllerDahlhaus and Vlachos, 2013). The configuration of the induced current flow (monophasic polarity, 500 Hz high-frequency bursts at theta rhythm, and motor threshold of stimulus intensity) via a standard figure-8 coil was tested to assess whether it was comparable or superior to the TMS-induced electric fields resulting from a single pulse (SP) or 500-Hz quadripulse single train stimulation of the motor cortex in healthy participants. We hypothesized that 500-Hz high-frequency monophasic TBS using TMS will strongly amplify MEPs and demonstrate a direct link between behavioral motor palsy and quantifiable functional parameters In this regard, we evaluated whether QTS-MEP potentials are quantifiable and beneficial neurophysiological biomarkers of functionally active corticospinal tracts at various degrees of motor paresis after stroke
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