“…The smallest interval explored was 6 msec, since it has been shown in a previous paper (Pierrot-Deseilligny et al 1976 belong to the fraction of the soleus a motoneurone pool which has already discharged in response to the conditioning volley (see above). In these motoneurones, the excitatory post-synaptic potentials resulting from the conditioning Ia afferent volley are eliminated by the action potentials they have elicited (Coombs, Eccles & Fatt, 1955b (Coombs, Eccles & Fatt, 1955a); (2) enhancement of the 324 B. BUSSEL AND E. PIERROT-DESEILLIGNY recurrent inhibition caused by the increased reflex discharge (H 1) in response to the SI conditioning volley (Ryall, Piercey, Polosa & Goldfarb, 1972); (3) activation, when the intensity of the conditioning stimulus is increased, of a larger number of either Ib fibres disynaptically inhibiting the homonymous motoneurones (Laporte & Lloyd, 1952), or of Ia fibres giving presynaptic inhibition of the test volley (Barnes & Pompeiano, 1970). Intensity of SI (mA) Fig.…”