After his experience, he investigated how the brain is wired to see if he could find a physiological explanation for his NDE. Alexander concluded that his experience could only be explained if consciousness does not require the brain for its existence. He also concluded that biological explanations such as abnormal CO2 and oxygen levels or abnormal brain chemicals like DMT or ketamine could not explain his experience. He said that before his NDE he believed Neuroscience could explain how the brain produced consciousness, but after the NDE he understood that "mind and consciousness are independent of the brain". This is extremely significant coming from a neurosurgeon who combines what he knows about Neuroscience and what he learned from his own near-death experience. Dr. Alexander states, "consciousness outside of the brain is a fact. It's an established fact."