The reference suggests the answer is somewhat nuanced; while not a literal "cleaning," dreaming does play a role in cognitive maintenance. Dream sleep helps to "tidy up" memories and feelings. The true brain "cleaning" through cerebrospinal fluid and the glymphatic system happens during deep sleep, not specifically during dreaming.
Therefore, dreaming is more accurately described as a memory and emotional consolidation process, contributing to cognitive health but not performing the same physical cleaning function as the glymphatic system during deep sleep.
