Variability of Intracortical Oscillations on Human Cortex and their Potential Relevance for Individualized Noninvasive Brain Stimulation

Background/Purpose: In neuronal developmental disorders, synaptic plasticity is discussed as a central pathophysiological role. In the induction of synaptic plasticity by transcranial magnetic stimulation (TMS), individual intracortical oscillations (I-waves) seem to be of importance. In particular, plasticity induction by individualized TMS might be central for clinical-therapeutic application. The aim of this study is to investigate the variability of I-waves.

Methods: I-waves were studied in posterior-anterior (PA) and anterior-posterior (AP) current flow directions in human primary motor cortex (M1) of 16 healthy subjects (24–34 years, w = 12) using a newly engineered stimulator. Paired pulses with interstimulus intervals of 0.1 to 6 ms in 0.1 ms steps with a biphasic pulse configuration were applied and the individual I-wave latencies were determined. For variability determination, a comparison with the intervals known from the literature (1.5 ms) was calculated.

Results: The I-waves showed interindividual variability compared with fixed interstimulus intervals (PA: I1 t(15) = −3.746, p = 0.002, d = −0.936; I2 (t15) = −3.943, p = 0.001, d = −0.985; I3 t(15) = 3.860, p = 0.002, d = 0.965; AP I2 t(14) = −4.178, p = 0.001, d = −1.078; I3 t(14) = 2.707, p = 0.017, d = 0.698).

Conclusion: The results suggest inter-individual variability of I-wave latencies. This could be a crucial factor in the development of individualized TMS protocols. Thus, the therapeutic effect, e.g., by combining TMS adapted to individual I waves with functional treatment in neuronal developmental disorders, could lead to sustained functional gains.

Publication History

Article published online:
28 October 2021