Figure 6. Effects of conditioning stimulation of group II afferents on responses of an intermediate zone interneurone evoked by group II afferents.

A and B, responses evoked by 5T stimulation of Q alone. C and D, responses evoked by the same stimuli following a short train of conditioning stimuli, at 5T, applied to the same nerve (at a conditioning-testing interval of 57 ms). E-H, corresponding control and conditioned field potentials. A, C, E and G, slow time base records with the corresponding records of afferent volleys from the surface of the spinal cord. B, D, F and H, expanded rightmost parts of records in A, C, E and G and PSTHs and cumulative sums of interneuronal responses evoked by 20 stimuli. Note that after the conditioning stimuli, the early responses disappeared and the neurone only responded at a longer latency. Dotted lines indicate latencies of monosynaptically and disynaptically evoked responses. Note also that the interneuronal spikes coincided with group II components of the field potentials, 0.5-1 ms from their onset. Field potentials were not properly recorded in B and C because low-cut filters were used while recording from interneurones for the purpose of constructing PSTHs.