[Ageing and central motor conduction time]

The corticomotoneuronal pathway in the aged was studied using the technique of percutaneous electrical stimulation of the brain and the spinal cord. Central motor conduction time (CMCT) from the cerebral motor cortex to the cervical segment of the spinal cord (C-CMCT) was measured in 26 intact volunteers (20-85 years old) by substracting the latency to onset of EMG activity of the thenar muscle after cervical stimulation from the latency to onset of EMG activity of the same muscle after cortical stimulation. The latencies to onset of action potential of the anterior tibial muscle after cortical stimulation and the onset of action potential of the same muscle after lumbar stimulation were also measured in 11 volunteers (aged 46-67 years), and the difference between the two latencies was evaluated as the central motor conduction time from the cortex to the lumbar segment of the spinal cord (L-CMCT). Mean C-CMCT was 5.1 ms. and mean L-CMCT was 12.8 ms. Neither was related to the patient's height or age. There was no difference in either C-CMCT or L-CMCT between males and females. The results suggested that the conduction of the pyramidal tract is not affected by age, and this must be recognised when motor functions in the aged are studied.