Typically, affected children survive only a few months after birth, but those that do survive seem to remarkably more conscious than you would guess based on theories that suggest the cortex is where all the action happens to support consciousness.
Swedish neuroscientist Bjorn Merker wrote an article [pdf] in February’s Behavioural and Brain Sciences journal arguing that these cases suggest we need to rethink our ideas about how the brain supports conscious thought, and perhaps, even consciousness itself.
Merker argues that the brain stem supports an elementary form of conscious thought in kids with hydranencephaly. It also contains auditory structures capable of preserving hearing in someone without a cortex. In contrast, optic nerve damage in hydranencephaly frequently impairs vision, regardless of what the brain stem does.
Self-awareness and other “higher” forms of thought may require cortical contributions. But Merker posits that “primary consciousness,” which he regards as an ability to integrate sensations from the environment with one’s immediate goals and feelings in order to guide behavior, springs from the brain stem.
If he’s right, virtually all vertebrates‚Äîwhich share a similar brain stem design‚Äîbelong to the “primary consciousness” club. Moreover, medical definitions of brain death as a lack of cortical activity would face a serious challenge. At the very least, physicians could no longer assume that individuals with hydranencephaly don’t need pain medication or anesthesia during invasive medical procedures.