Rapid on-line estimation of responses to transcranial magnetic and peripheral nerve electrical stimulation in single human motoneurons.

Cross-correlation experiments allow to obtain information about synaptic potentials in human motoneurons. However, recording cross-correlation responses of one motoneuron to transcranial magnetic and electrical peripheral nerve stimulation requires a considerable recording time when both responses are recorded consecutively. In this paper a method is introduced yielding the same information about the responses of a single motoneuron to both types of stimuli while requiring only a fraction of the recording time necessary for a conventional cross-correlation experiment. The main features of the method introduced were: (i) use of the recharging time of the magnetic stimulator for response recording to the electrical stimulus, (ii) use of specific stimulus timing with respect to the motor unit discharges, and (iii) on-line display with statistical testing of the response functions allowing to stop stimulus application, if the responses to both types of stimuli had reached statistical significance. Application of the method is demonstrated with response recording of 70 tibialis anterior motor units from five healthy volunteers to transcranial magnetic and peroneal nerve electrical stimulation.