FIGURE 8-12 Neuronal Maturation in Cortical Language Areas In postnatal cortical differentiation—shown here around Broca’s area, which controls speaking—neurons begin with simple dendritic fields that become progressively more complex until a child reaches about 2 years old. Brain maturation thus parallels a behavioral development: the emergence of language.

Figure from Biological Foundations of Language (pp. 160–161), by E. Lenneberg, 1967, New York: Wiley.