In 2014, a month-long bout of dizziness and vomiting brought a 24-year-old woman in China to the hospital. She was no stranger to these symptoms: she’d never been able to walk steadily and suffered from dizziness nearly her whole life. These were serious, debilitating symptoms. And yet, they might have seemed almost mild once CT and MRI scans presented a diagnosis: the woman was missing the majority of her brain – in a manner of speaking.
Yes, most of the players on the brain’s ‘stage’ were present: the cerebral cortex, the largest, outermost part of the brain responsible for most of our thinking and cognition, was present and accounted for; the subcortex and the midbrain, with their myriad functions involving movement, memory and body regulation – also present; the brainstem, essential for controlling breathing, sleep and communicating with the rest of the body – present and accounted for.
But none of these arenas hold the majority of the brain’s currency – neurons, the cells that fire impulses to transmit information or relay motor commands. This distinction goes to the cerebellum, a structure situated behind the brainstem and below the cerebral cortex. Latin for ‘little brain’, the highly compact cerebellum occupies only 10 per cent of the brain’s volume, yet contains somewhere between 50 and 80 per cent of the brain’s neurons.
And indeed, it was in this sense that the hospitalised Chinese woman was missing the majority of her brain. Incredibly, she had been born without a cerebellum, yet had made it through nearly two and a half decades of life without knowing it was missing. Compare that with strokes and lesions of the cerebral cortex, whose neuron-count is a fraction of the cerebellum’s. These patients can lose the ability to recognise colours or faces and to comprehend language – or they might develop what’s known as a ‘disorder of consciousness’, a condition resulting in loss of responsiveness or any conscious awareness at all.
Understanding consciousness might be the greatest scientific challenge of our time. How can physical stuff, eg electrical impulses, explain mental stuff, eg dreams or the sense of self? Why does a network of neurons in our brain feel like an experience, when a network of computers or a network of people doesn’t feel like anything, as far as we know?
Alas, this problem feels impossible. And yet, an unmet need for progress in disorders of consciousness, in which the misdiagnosis rate is between 9 and 40 per cent, demands that we try harder. Without trying harder, we’ll never know if injured patients are truly unconscious – or unresponsive but covertly conscious with a true inner life. Without this knowledge, how can doctors know whether a patient is likely to recover or whether it’s ethical to withdraw care?