P 97. Could plasticity-like changes be qualified by the evolution of complexity in transcranial magnetic stimulation induced surface EMG?

• Published in: Clinical neurophysiology Vol. 124; no. 10; p. e111
• Main Authors: Cukic, M., Kalauzi, A., Ljuibisavljevic, M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ireland Ltd 01.10.2013
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2013.04.175

The aim of this study was to determine whether a single-pulse TMS induces changes in complexity of surface EMG immediately after the stimulation. We analyzed changes in Fractal Dimension (FD) in FDI muscle of the dominant hand in 9 healthy subjects, while exerting three intensities of voluntary activation: weak (<30% of MVC), medium (30–60%) and strong (>60%); control group were 5 healthy volunteers sustaining the same three levels of contraction without presentation of TMS. FD was calculated using Higuchi’s algorithm, on EMG immediately after TMS-induced silent period and compared with those calculated from preceding TMS EMG sections; FD with moving window was used to depict the curves of complexity changes, and then we performed FFT on the data. All analysis were performed in response to three intensities of TMS stimulation set at 1.1×MT, 1.2×MT and 1.3×MT (Motor threshold MT). Ten single TMS stimuli were delivered in each series using a figure-of-eight coil positioned over the optimal spot on the skull to elicit MEP from FDI muscle. The FD of the EMG after TMS fell (compared with the values of FD from the EMG section of the record before TMS) in the majority of examined series of recordings (in 72 out of 90 series), and cyclic-like changes were observed in all the curves constructed. Statistically significant changes in FD of series ‘before’ and ‘after’ were found more frequent for recordings during sustaining mild and medium MVC, than in strong MVC (p<0.05). It appears that single pulse TMS of the motor cortex induces plasticity-like changes in the voluntary EMG signal.