Brain growth was studied from day of birth through 23 days of age in three outbred and one inbred groups of mice. The results showed that the brain grows rapidly from Birth through 11 days and quite slowly thereafter. We found no evidence of the several spurts and plateaus in growth that are central to the theory of phrenoblysis (correlated brain and mind growth). Our results show the main features of mouse brain growth to parallel those of human brain growth except for timing of rapid and slow growth.

Epstein has suggested that normal brain development is characterized by spurts and plateaus. In mice, these spurts seem to appear at 0-6,8-12 or 13, and 17-23 days, and plateaus appear at 6-8,12-17, and after 23 days of age. Results have demonstrated enhanced learning in a spurt (11 and 19 days of age) and a decrement in learning at a plateau (15 days of age), using an active avoidance task to measure learning in Fuller BWS high and low brain-weight lines. We tested Fuller BWS high-and low-line mice in a passive avoidance task at 11, 15, and 19 days of age. Mice were also tested at 12 days of age, since a recent study found that 12-day-old mice are in a plateau rather than a spurt, as previously reported. As high activity levels may conflict with the response made, activity levels were also measured on the day of testing. The results revealed an age effect and an Age by Line interaction, but no line effect: Mice at 11 and 19 days of age (spurts) differed significantly from mice 15 and 12 days of age (plateaus). Activity was not found to be a confounding measure.Recent work has shown that brain size can be influenced by variables such as nutrition, environment, maternal behavior, and genes (Hahn, Jensen, & Dudek, 1979). It also appears that brain size is related to behavior, as species with larger average brain size in relation to average body size show greater ability to process and utilize information. Epstein (1979) has shown a stagewise growth in average brain weight, and he correlates these braingrowth stages with mind-growth stages, or Piaget's stages of intellectual development. He suggests that the normal course of human brain development is not a linear process but, rather, is characterized by specific stages of rapid and slow growth, or spurts and plateaus, respectively.A study by Gottlieb, Keydar, and Epstein (1977) on mouse and rat brain growth from birth to weaning shows rapid growth (spurts) at 0-6, 8-12 or 13, and 17-23 days, and slow growth (plateaus) at 6-8,12-17, and after 23 days of age. Epstein's (1979) work predicts a decrement in learning ability at a plateau and increased learning in a spurt.