Summary of firing rate development. Development of the activity levels in ghrelin treated cultures (ghr, n = 11) and controls (ctrl, n = 7). (A) The average activity levels of both groups at different culture ages, up to 30 days in vitro (DIV). Error bars indicate the SEM and reflect differences between cultures. *indicates a significant difference (p < 0.04; 2-tailed t-test, unequal variances). The absolute activity levels differed substantially between cultures within either group. To emphasize the rate of development at different ages, we normalized the activity development of all individual experiments to a mean value of 1 before averaging across cultures. (B) The mean normalized activity levels at different ages. Error bars indicate the SEM. *indicates a significant difference (p < 0.01; 2-tailed t-test, unequal variances).