Neuronal plasticity II: modulation of cortical excitability

Objective: The aim of modulation of cortical excitability is the improvement of training based neuronal plasticity. The aim of this study was the modulation of cortical excitability by selective regional plexus anaesthesia of the upper arm.

Methods: Plexus brachialis (C5– C6) was selectively blocked and a standardised metronom triggered pinch training of the M. flexor pollicis brevis was performed. The motor evoked potentials (MEP) amplitude and the cortical excitability were measured before and after this intervention by ftmS after 1, 3, 5 and 10 ms (n=6 healthy adults) with paired pulse technique. The cortical excitability results were polled in a variable of the paired puls excitability.

Results: In five adults (one was excluded after ineffective plexus block) the paired-pulse excitability increased significantly (0.81 to 1.27, Wilcoxon test p=0,043) after selective regional plexus anaesthesia of the upper arm and repetitive training. A clearly increase of the MEP amplitude was shown in three probands (MEP 452.38 to 840.53).

Conclusion: The cortical excitability is modulated by selective regional plexus block, demonstrated by us for the first time by significant reduction of the intracortical inhibition. A reduction of the intracortical inhibition and an increase of the cortical excitability increase the capacity of training induced neuronal plasticity. The modulation of cortical excitability may explain the motor improvement at stroke patients after selective regional plexus anaesthesia of the upper arm (Muellbacher et al., 2002).

Keywords: cortical plasticity, tmS, regional plexus anaesthesia, deafferentation