Sleep Can Be Considered an Altered State of Consciousness; Not

Sleep can be considered an altered state of consciousness; not unconsciousness. Moreover, it is well known that sleep is needed to consolidate learning and memories. Studying the rhythmicity of the _______, therefore, will likely yield the most useful information about why we need to sleep.

A) respiratory centers in the medulla
B) suprachiasmatic nucleus in the hypothalamus
C) hippocampus and association cortices
D) spinal cord
E) visual cortex