Comments on 'the discrepancy between human peripheral nerve chronaxie times as measured using magnetic and electric field stimuli: the relevance to MRI gradient coil safety'.

A recent electrostimulation study with human subjects (Recoskie et al 2009 Phys. Med. Biol. 54 5965-79) reported a large difference between chronaxie times when stimuli were delivered to the same body locus (the wrist) either through contact electrodes (electric stimulation) or through a pulsed magnetic field (magnetic stimulation). This paper reviews the procedures and analytic methods used in that study that might account for the reported discrepancies. Factors possibly accounting for reported discrepancies include the maximum and minimum pulse widths of the experimental stimuli; variations in experimental waveforms vis-à-vis mathematically ideal functions; differences in the spatial distribution of the in situ electric field for the two methods of delivery and differences in derived chronaxie relative to strength-duration time constants.