[Neurophysiological analysis of interhemispheric motor tracts in neurodegenerative diseases]

The corpus callosum (CC) is the morphological correlate of inter-hemispheric connectivity. Its integrity is of great importance for motor function and inter-hemispheric coordination of bimanual movements. Callosal fibre tracts show a high vulnerability as they are involved in number of neurodegenerative disease like parkinsonian syndromes and amyotrophic lateral sclerosis, even at early stages of the diseases. The integrity of callosal fibre bundles may be investigated by magnetic resonance imaging techniques and electrophysiologically by transcranial magnetic stimulation (TMS) investigating the transcallosal inhibition (TI). TMS investigation of the TI may be performed by measurement of the ipsilateral silent period (iSP). Most common findings are a loss or a prolongation of the iSP latency. Alternatively, a double pulse paradigm may be used to demonstrate altered TI. Furthermore, the transcallosal conduction time may be lengthened. TMS investigation of TI may a helpful diagnostic tool and may give new insights into the pathophysiology.