Study of the effects of a 5-day brain stimulation with Paired Associative Stimulation (PAS) against placebo in 28 hemiplegic patients

Abstract

The Paired Associative Stimulation (PAS) is a non-invasive brain stimulation technique combining an electrical peripheral stimulation and a magnetic cortical stimulation. Applied on the wrist extensor muscles, one session induced changes in cortical excitability. We studied the effects of a repetition of 5 PAS sessions against placebo. This is a prospective, randomized, double-blind against placebo study. One session consisted in applying an electrical peripheral stimulation on the wrist extensor muscle followed by a 25-ms later magnetic cortical stimulation over the wrist area, at a 0.1-Hz frequency during 30 minutes, the patient receiving 180 paired stimuli. In the SHAM group, the patient received the electrical peripheral stimulation and a SHAM magnetic stimulation. One session was applied every day during 5 days. The changes in area of the motor-evoked potential (MEP), reflecting the changes in cortical excitability, and motor changes studied by the Fugl-Meyer score were assessed at the end of the 1st and 5th session, 3, 5 and 7 days after the end of the 5 days session. Twenty-eight patients were included (19 men, mean age: 49.9 ± 13.5 years), with stroke from 10.0 ± 5.1 weeks. Only data from 24 patients were exploitable, 13 patients being included in the PAS group. It was not found significant differences between the two groups regardless of the time after stimulation, or the electrophysiological parameters, neither the motor scores. However, there is a greater MEP variability in the PAS group compared to the SHAM group. All patients ( n = 5) for which PAS increased cortical excitability (D8-MEP > +200% D1-MEP) were those with a low initial level of cortical excitability. The initial level of cortical excitability seems to play a key role of repeated sessions of PAS on the lasting effects on brain plasticity. Our results confirm the importance of the initial level of neuronal activation in the cortical modulation induced by TMS.