Sustained upgaze in coma.

Sustained upgaze is a rare phenomenon that is observed primarily in those patients with coma secondary to cardiac arrest or prolonged hypotension. Because of "selective vulnerability" of the brain, cardiac arrest or prolonged hypotension may produce both cerebral and cerebellar cortical damage sparing the brain stem vestibulo-ocular reflex (VOR) pathways. This selective damage may be responsible for the generation of sustained upgaze. The VORs receive their selective inhibition from the cerebellar flocculus. This inhibition is exerted on only one of the two VOR pathways converging on each extra-ocular muscle, so that total disinhibition of the VOR pathway activities will result in a tonic upward bias. The underlying neuronal mechanism of sustained upgaze appears to be due to total floccular disinhibition resulting in upward drift produced by the biased VOR and the lack of correcting saccades due to cerebral dysfunction releasing the brain stem ocular motor systems from their control.