Many doctors and biomedical students may have been taught the same about consciousness. However, scientists are still debating whether that theory holds true.

Imagine a child observing an elephant for the first time. Light reflects off the animal and enters the child's eyes. Retinal photoreceptors in the back of the eyes convert this light into electrical signals, which travel through the optic nerve to the brain's cortex. This forms vision or visual consciousness.

How do these electrical signals miraculously transform into a vivid mental image? How do they turn into the child's thoughts, followed by an emotional reaction—"Wow, the elephant is so big!"

The question of how the brain generates subjective perceptions, including images, feelings, and experiences, was coined by Australian cognitive scientist David Chalmers in 1995 as the "hard problem."

As it turns out, having a brain may not be a prerequisite for consciousness.

'Brainless' but Not Mindless

The Lancet recorded a case of a French man diagnosed with postnatal hydrocephalus—excess cerebrospinal fluid on or around the brain—at the age of 6 months.

Despite his condition, he grew up healthy, became a married father of two children, and worked as a civil servant.

When he was 44 years old, he went to the doctor due to a mild weakness in his left leg. The doctors scanned his head thoroughly and discovered that his brain tissue was almost entirely gone. Most of the space in his skull was filled with fluid, with only a thin sheet of brain tissue.

"The brain was virtually absent," wrote the lead author of the case study, Dr. Lionel Feuillet, of the Department of Neurology, Hôpital de la Timone in Marseille, France.

The man had been living a normal life and had no problem seeing, feeling, or perceiving things.