Motor axon reflex and indirect double discharge: ephaptic transmission? A reappraisal.

Causal mechanisms of the motor axon reflex (MAR) and indirect double discharge (IDD) are re-examined. The hypothesis that these indirect intermediate latency responses result from an axono-axonal ephaptic transmission mechanism has recently been suggested. The various conceivable responses of models of axonal cross-talk are compared with actual observations made from the limbs. We conclude that the ephaptic hypothesis does not explain MAR and IDD, and that the earlier understanding that MAR results from axonal branching and IDD from proximal re-excitation on the axon holds true.