A, modulation of monosynaptic field averaged across all datasets following conditioning stimulation of the PT or peripheral nerve. B, percentage occurrence of individual facilitation effects which were individually significant at the P < 0.05 level. No significant suppression events were observed following stimulation of any peripheral nerve. (PT, three datasets; nerve, eight datasets). C, modulation of monosynaptic field potential plotted against modulation of antidromic cortical field by preceding PT stimuli for interstimulus intervals between 5 and 50 ms. The magnitudes of the conditioning effects are proportional over the range 15–50 ms.