Kaplan-Meier presentation of overall group performance in mice. Curves represent group performance (n = 13–15 per group). They indicate the cumulative probability of members of each group not to finish the task (that is, not to reach performance criteria in the 1.0-sec stimulus duration phase). EPO-treated mice are superior, that is, have a lower probability not to finish the task as compared with no-inject and placebo groups. On day 59 after cessation of treatment, the first mouse reached criteria in the 1.0-sec phase. This mouse belonged to the EPO group. Day 94 is the time point on which > 60% of one experimental group (here the EPO group) had finished the task.