Age dependence of interhemispheric inhibition of the motor cortex in humans

Ongoing voluntary electromyographic activity of the small hand muscles can be suppressed by a single focal magnetic stimulus applied to the ipsilatera l motor cortex. This inhibition is mediated from one motor cortex to the co ntralateral side via a transcallosal pathway. We investigated the transcall osal inhibition in 24 healthy volunteers aged 26-80 years. The aim of this study was to investigate a possible correlation between the age and the gen der of the subjects and the parameters of the transcallosal inhibition. A f ocal magnetic stimulus was applied to the hand area of the motor cortex and the onset latency of the inhibition of the ongoing EMG activity of the ips ilateral first dorsal interosseus muscle was evaluated. Corticomuscular con duction time to the same muscle was measured using a magnetic stimulus over the contralateral motor cortex. The difference between these values was ca lculated as transcallosal conduction time. All subjects had a transient com plete inhibition of the EMG; activity of their ipsilateral first dorsal int erosseus muscle. The transcallosal conduction time was 12.2 +/- 2.6 ms and the duration of the inhibition was 38.9 +/- 10.1 ms. No statistically signi ficant correlation between the age of the subjects and the transcallosal co nduction time or the depth of the inhibition could be found. There was no s ignificant difference between the transcallosal inhibition of the hemispher es or between both genders.