FIG. 6.

The sensory evoked potential (SEP) paired-pulse (PP) ratio in contralesional cortex is significantly increased at 3 days and 4 weeks after traumatic brain injury. (A) An example plot of the paired-pulse design used, showing the stimulus artifacts (stim1, stim,2), the inter-stimulus interval (ISI) used to delay the onset of the second stimulus, and the resulting SEP pulses (P1, P2, N1) recorded following each stimulus. The pulses immediately following the first and second stimuli (P1A, P1B, respectively) were quantified. (B) Group-averaged, SEP signal of the PP stimulus response at 50-200 msec ISI averaged from all electrode pairs, and temporally realigned to the first stimulus artifact to illustrate the lowered second peak amplitude at 100 msec ISI, especially at 4 weeks compared with pre-injury, giving rise to reduced P1B/P1A PP ratios. (C) Plot of PP ratio data values from all electrode pairs (apart from two posterior pairs that responded differently; Fig. 7B) and for all post-injury time-points as a functions of ISI time, showing a significant difference at 28 days post-injury at a 100 msec ISI and a trend at 3 days. (D) Plots of PP ratio values for each ISI value versus post-injury time and normalized by individual rat pre-injury value. Data shows non-significant trends toward increased PP ratios at 35, 50, and 200 msec ISI at most post-injury times, and a significant increase at 3 and 28 days at 100 msec ISI. *p < 0.05 (Linear mixed models analysis of variance, Dunnett-corrected multiple-comparisons on raw data). Horizontal dotted line = mean pre-injury values.