Figure 5. Comparison of PSPs evoked by stimulation of MLF alone and when preceded by stimulation of iPT or co PT after tDCS.

(A–C and D–F), intracellular records from two GS motoneurons penetrated in the same experiment after tDCS (upper traces; averages of 20 records) and the corresponding records from the cord dorsum. Upper row, effects of a train of four stimuli applied in the MLF alone. Middle and bottom row, effects of the same stimuli preceded by four stimuli applied to either iPT or co PT, as indicated, with EPSPs evoked by MLF alone (grey) superimposed. Large arrows indicate the earliest EPSPs. Small arrows indicate MLF volleys followed by these EPSPs. The increases of EPSPs evoked by second stimulus in % of control are indicated in B and E. Other indications are as in Fig. 2. (G), the diagram showing the stimulation and the recording sites and the involved inhibitory interneurons. (H), decreases in the latencies (mean latencies and SEM; from the first MLF stimulus) of EPSPs and IPSPs evoked by MLF or by joint iPT and MLF stimuli. After tDCS the decreases in latencies of the joint iPT-MLF actions (shaded columns) were significantly larger with respect to EPSPs evoked by both iPT and MLF stimuli under control conditions and only MLF stimuli after tDCS (*p<0.05, t-test paired data; *** p<0.001 t-test two samples). (I), increases in amplitudes of EPSPs and IPSPs evoked by MLF stimuli when combined with iPT stimuli (* p<0.05 t test for either paired data or two samples). In (H) and (I) are data for 10 and 12 motoneurons in which EPSPs were recorded before or during/after tDCS and in 9 and 14 motoneurons in which effects of tDCS were compared on IPSPS.