Fig. 3. Effect of 30% nitrous oxide on second population spike at 42-ms interstimulus intervals. a) The ratios of second population spike/first population spike remained stable at a 42 ms interstimulus interval (pre-nitrous oxide  versus nitrous oxide; 0.88 ± 1.10  versus . 0.87 ± 0.12;  P = NS by paired Student  t test, n = 6). b) At an interstimulus interval of 42 ms, traces show representative population spike before (  solid ) and 20 min after (  dotted ) nitrous oxide administration. c) The graph shows input-output curves for second population spike amplitude recorded before (  diamonds ) and 20 min after (  squares ) nitrous oxide administration from a single slice at an interstimulus interval of 42 ms. Nitrous oxide did not change second population spike based on input/output curves.