Doctors in Cincinnati who are treating the American college student released by North Korea in a coma say he has severe injury to all regions of his brain.

On Thursday, they described 22-year-old Otto Warmbier as in a state of “unresponsiveness wakefulness.”

They say he doesn’t show any consistent response to stimulation, shows no sign of understanding language, responding to commands or awareness of his environment.

Doctors with the University of Cincinnati Health System say Warmbier shows extensive loss of brain tissue, consistent with respiratory arrest, when oxygen to the brain is cut off, but they aren’t sure why.

They said his prognosis remains confidential.

Warmbier is in stable condition at UC Medical Center, where he was taken Tuesday night after his arrival in Ohio.