Functional plasticity induced by mirror training: the mirror as the element connecting both hands to one hemisphere.

BACKGROUND: Mirror therapy (MT) is a promising therapeutic approach in stroke patients with severe hand paresis. OBJECTIVE: The ipsilateral (contralesional) primary sensorimotor cortex (SMC) and the mirror neuron system have been suggested to play decisive roles in the MT network. The present study investigated its underlying neural plasticity. METHODS: Two groups of healthy participants (n = 13 in each group) performed standardized fine motor tasks moving pegs and marbles (20 min/d for 4 days) with their right hand with either a mirror (mirror training group, MG) or a nonreflective board (control training group, CG) positioned orthogonally in front of them. The number of items moved by each hand was tested after each training session. Functional MRI (fMRI) was acquired before and after the training procedure to investigate the mirror training (MTr)-specific network by the analysis of the factors Time and Group. RESULTS: The hand performance test of the trained right hand did not differ between the 2 groups. The untrained left hand improved significantly more in the MG compared with the CG. fMRI analysis of action observation and imitation of grasping tasks demonstrated MTr-specific activation changes within the right dorsal and left ventral premotor cortex as well as in the left SMC (SMC(left)). Analysis of functional and effective connectivity showed a MTr-specific increase of functional coupling between each premotor region and the left supplementary motor area, which in turn showed an increased functional interaction with the ipsilateral SMC(left). CONCLUSIONS: MTr remodels the motor system by functionally connecting hand movement to the ipsilateral SMC. On a system level, it leads to interference of the neural circuit related to motor programming and observation of the trained hand with the illusionary movement of the untrained hand.

Changes in intracortical excitability after successful epilepsy surgery.

Interictal activity from epileptic foci may have remote effects as demonstrable by assessing brain perfusion, metabolism and excitability. So far, the effect of surgical removal of the epileptic focus on cortical networks has only rarely been addressed. This study aims at an assessment of changes in intracortical inhibition and excitability in patients undergoing successful epilepsy surgery. Twenty-two patients (12 females, 10 males, mean age 37.8 years) with identical pre- and postsurgical antiepileptic medication were investigated using focal transcranial magnetic stimulation. Motor thresholds (MT), contralateral cortical silent periods (CSP) and amplitudes of motor evoked potentials (MEP) using paired pulse paradigms were investigated both, at the focal and non-focal hemisphere before and at least 3 months after successful epilepsy surgery. The postsurgical mean MT when stimulating at the focal hemisphere was significantly higher than at the non-focal hemisphere (p=0.01). Postsurgically, the mean duration of the CSP at 120% and at 150% of MT of the non-focal hemisphere was significantly shorter than presurgically (p=0.04), and the mean MEP amplitude following paired-pulse stimulation with an interstimulus interval of 10 ms of the non-focal hemisphere was significantly lower than presurgically (p=0.03). In summary, both parameters representing inhibition and facilitation changed following epilepsy surgery; effects were statistically significant on the non-focal hemisphere. Transcranial magnetic stimulation thus gave evidence of remote effects of an epileptic focus and its surgical removal. Extended changes in excitability due to the presence or absence of an epileptic focus may be related to widespread functional impairments in patients with focal epilepsy.