P 86 Plasticity induction in humans by individualized quadri theta burst stimulation – preliminary results

• Published in: Clinical neurophysiology 2022-05, Vol.137, p.e65-e66
• Main Authors: Brich, L., Gleich, B., Schaff, F., Heidsieck, A., Sandurkov, B., Mall, V., Jung, N.
• Format: Article
• Language: English
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2022.01.117

Introduction: Synaptic plasticity in the form of long-term potentiation (LTP) and long-term depression (LTD) is considered a neurophysiological correlate of learning and memory processes that can be studied using transcranial magnetic stimulation (TMS). TMS over the primary motor cortex (M1) produces descending volleys (I-waves) with three main maxima that appear to play a role in plasticity induction. Their latencies can be determined by short-interval intracortical facilitation (SICF) and show interindividual variability. “Individualized quadri theta burst stimulation” (iqTBS) adapted to I-waves could lead to an increase in corticospinal excitability. The aim of this study was to investigate the effects of iqTBS, in posterior-anterior (PA) and anterior-posterior (AP) current flow directions on corticospinal excitability in humans. Material & Methods: I-wave latencies were studied in PA (experiment I) and AP (experiment II) current flow directions across the M1 in 12 healthy subjects (24-34 years, w = 8) using a newly developed stimulator (MIBE). Paired pulses with interstimulus intervals of 0.1 ms to 6 ms in 0.1 ms steps with a biphasic pulse configuration were applied. The iqTBS consisted of 1440 full-sine pulses given continuously to M1 with bursts of four TMS pulses separated by individually set interstimulus intervals. To determine the change in corticospinal excitability, motor evoked potential (MEP) was recorded before and up to 1 h after iqTBS. For statistical analysis rmANOVA and t-tests were performed. Results: Preliminary results show an increase in MEP amplitude in both experiment I (PA) and experiment II (AP) after iqTBS matched to individual I-wave latencies. MEP amplitude already increased in experiment I immediately after iqTBS, whereas it showed a significant increase after 15 minutes in experiment II. Conclusion: The iqTBS adapted to individual I-wave latencies showed a significant increase in corticospinal exitability over M1 in humans in both PA and AP current flow directions. In contrast to qTBS with fixed interstimulus intervals of 1.5 ms, which induces current flow dependent bidirectional plasticity, iqTBS also showed it in PA current flow direction. The results may indicate possible high fidelity spike-timing dependent plasticity mechanisms. The results could play a role in basic-scientific applications of high-frequency TMS in humans and enable individualized non-invasive brain stimulation in a clinical therapeutic context, e.g.,