The Effects of Motor Imagery and Paired Associative Stimulation on Cortical Excitability

Kumpulainen, Susanne 2009. The effect of PAS and motor imagery on the excitability of the motor cortex. Department of Biology of Physical Activity, University of Jyväskylä. Master’s theses of biomechanics. 41 pages. The plasticity of the brain is an increasingly important topic for physical therapists interested in (re)learning and repair following injury. A number of potential endogenous and exogenous protocols have been developed with the improved understanding of the mechanisms of synaptic plasticity. The purpose of this study was twofold: First, the effect of motor imagery of plantarflexion on motor cortex excitability was investigated since it has been shown that motor imagery may result in the same types of plastic changes in the motor system as actual physical practise. The second aim was to study the effect of facilitatory paired associative stimulation (PAS) on motor imagery. PAS is an exogenous protocol which has been used to induce bidirectional changes in the motor cortex excitability. Transcranial megnetic stimulation was used to measure changes in the motor evoked potentials (MEPs) of the soleus muscle with, and without, motor imagery and before, immediately after, and 15 min after the PAS intervention. During motor imagery of plantar flexion, a remarkable increases in the amplitude of the MEP of the soleus were observed with each time points 76 ± 62 %; 30 ± 33 % and 31 ± 50 %, respectively. The lack of background EMG assured that changes weren’t associated with muscle activity. Interestingly, instead of facilitatory PAS, the protocol induced a remarkable inhibitory PAS. Inhibition was bigger with the motor imagery condition (38 ± 19 % and 31 ± 28 %) compared to the passive condition (16 ± 26 % and 5 ± 37 %), suggesting that the effect of PAS was more substantial during motor imagery. It can be concluded that the use of motor imagery in neurological rehabilitation may be defended on the basis of these results.