Taxometric analysis of biceps femoris EMG following electrocutaneous stimulation over the sural nerve: Determining the latent structure of the nociceptive flexion reflex (NFR)

The nociceptive flexion reflex (NFR) is a polysynaptic withdrawal reflex typically assessed from biceps femoris electromyogram (EMG) following noxious stimulation of the ipsilateral sural nerve. Electrophysiological evidence suggests the reflex is elicited following the activation of small diameter A-delta afferents. As a result, the NFR is assumed to be a categorically distinct construct that emerges from EMG activity only following nociceptor activation. Despite the widespread use of the NFR in pain research, there has been little attempt to verify the latent structure of the NFR. The present study used “coherent cut kinetics” taxometric analyses to examine whether the latent structure of biceps femoris EMG reflects the taxonic structure that would be predicted from electrophysiological evidence. To achieve this end, preliminary analyses first compared different methods of scoring NFR magnitude. Results suggested the presence of a taxon in the covariance of biceps femoris EMG and stimulus intensity that is likely to be the NFR. Furthermore, preliminary analyses suggested the best method of scoring NFR magnitude was using Cohen's d. Implications of these results are discussed.