Reliable longitudinal research on the brain as it is growing from childhood into adolescence showed:

Reliable longitudinal research on the brain as it is growing from childhood into adolescence showed "a decrease in gray matter and an increase in white matter".

Gray matter is a noteworthy segment of the central nervous system, comprising of neuronal cell bodies, neuropil (dendrites and myelinated and in addition unmyelinated axons), glial cells (astrocytes and oligodendrocytes), neurotransmitters, and vessels.  

Gray matter is recognized from white matter in that it contains various cell bodies and moderately couple of myelinated axons, while white issue contains generally few cell bodies and is made primarily out of long-run myelinated axon tracts. The color distinction emerges basically from the whiteness of myelin. In living tissue, dim issue really has a light dark shading with yellowish or pinkish tones, which originate from capillary blood and neuronal cell bodies.

answer; i believe the correct answer is enlightenment;

the branch of biology that deals with the normal functions of living organisms and their parts.

the way in which a living organism or bodily part functions.