Myelination of language-related areas in the developing brain

Background: The rapid development of language abilities in early childhood coincides with a similarly accelerated progression in brain maturation. Objective: To quantitate myelination in the lateral part of the verbal left hemisphere from birth to 3 years in the living human brain. Methods: One hundred children (mean age 16.6 months) were examined using three-dimensional MRI, and a subgroup of 40 children were also evaluated behaviorally. The volume of myelinated white matter was measured in language-related temporal and frontal regions and in the central sensorimotor region. A method was developed to compose a movie sequence for all the myelination process using volumetric data. Results: A plot of age against relative volume of myelinated white matter graphically detailed the myelination progress in the lateral brain. The changes started in sensorimotor white matter and the Heschl gyrus and ultimately extended to the language-related areas. Both comprehension and production regions showed a very similar myelination course, suggesting simultaneous maturation of the temporofrontal language network. The movie sequence of white matter images dynamically displayed the anatomic details of myelin deposition in this part of the brain. The analysis of language performance showed acceleration in children's vocabulary after 18 months, once a rapid myelination phase was attained in the language brain. Conclusions: This volumetric study may contribute to further characterize the early stages of brain maturation by showing the fine progression of myelin deposition in the language domains and illustrating its relationship to children's vocabulary acquisition.