Complex sentence: Bartzokis et al., has noted that there is a decrease in grey matter volume between adulthood an old age, whereas white matter volume was found to increase from age 19-40, and decline after this age.
Split into simpler sentences: Bartzokis et al., has noted that there is a decrease in grey matter volume between adulthood an old age. Whereas, white matter volume was found to increase from age 19-40, and decline after this age.