Figure 3.

Temporally correlated motor unit activity is increased in MK801-injected compared with saline- or PCPA-injected P7–P8 pups. A, B, Raw EMG records (A) and waveform overlays of two discriminated motor units (B) (calibration bars: 0.3 mV, 10 s and 3 ms, respectively). C, Temporal correlations were seen in motor unit recording from MK801-injected pups, indicated by peaks in the cross-correlograms. The left cross-correlogram from a PCPA-injected mouse shows no correlation. The middle and right cross-correlograms (constructed with 100 and 10 ms bins, respectively) are from the same MK801-injected animal and show temporal correlation over a period of 1.4 s. D–F, The strength of temporal correlation for each motor unit pair was determined by the index k′ − 1 (D) and by the correlation index over 20 ms (E) and 100 ms (F) intervals. Values for each motor unit pair are shown (black circles, saline; white circles, PCPA; black triangles, MK801). The connected circles (black) represent the mean ± SEM index values for the saline, PCPA, and MK801 experimental groups. The index k′ − 1 was significantly increased in MK801-injected pups (p = 0.001, ANOVA on ranks with Dunn's post hoc test). A similar increase was also seen in the correlation index over 20 ms bins (p = 0.014) and 100 ms bins (p = 0.005, ANOVA on ranks with Dunn's post hoc test; n = 8–11 motor unit pairs).