What developmental condition is characterized by excessive proliferation of neural stem cells?

The correct answer is indeed characterized by excessive proliferation of neural stem cells. Megalencephaly refers to an abnormal increase in the size of the brain, which can result from various factors, including an overproduction of neural stem cells during development. This condition can lead to an enlarged head size in infants and a variety of associated neurological issues.

This occurs because the regulated process of neurogenesis, which involves the proliferation, differentiation, and maturation of neural stem cells into neurons, can become dysregulated. An overabundance of stem cells can lead to excess neuron production, contributing to the larger brain size observed in megalencephaly.

In contrast, microcephaly is characterized by a smaller-than-normal head size, often arising from various genetic and environmental factors that inhibit normal brain development. Asymmetrical division refers to a specific mode of cell division that results in daughter cells with different fates, which can be an aspect of neurogenesis but does not define a developmental condition. Neurogenesis itself refers to the process of generating new neurons and is not a condition but rather a normal biological process that includes both proliferation and differentiation of neural stem cells.