This week’s Nature has an intriguing short paper by a team of neuroscientists who ‘awoke’ a man from a ‘minimally conscious state’ by activating a surgically implanted brain electrode.
Like a coma, ‘minimally conscious state‘ (MCS) occurs after severe brain injury, but is not a state of complete unconsciousness.
Instead, the patient seems mostly unresponsive but can occasionally produce simple responses to commands or prompts that suggest inconsistent consciousness, such as short purposeful actions, brief verbalisations or emotional reactions.
Like coma, MCS is not a caused by a specific type a brain injury. It’s a description of the person’s behaviour, so it could be caused by varying damage to a wide range of brain systems.
However, it is known that MCS can be caused by problems with arousal. In other words, the major brain systems of the cortex might be relatively intact, but the system that regulates how active they are might be damaged, meaning the person has trouble staying conscious, despite having the potential for possible quite complex mental processes.
The frontal lobes, the brain stem and the thalamus are known to be key parts of the arousal system.
The man in question had been in a MCS for six years after suffering an assault with a blunt instrument that caused haematoma – bleeding in the brain, and subsequently, hydrocephalus – a build up of cerebral spinal fluid. Both of which put pressure on the brain that deformed and damaged it.
Because the man in question could intermittently respond to commands and give verbal responses, the researchers thought this might be a case where impaired arousal might be responsible.
To try and boost the activity in his arousal system, the team implanted a deep brain stimulation device (DBS) that sent electrical pulses directly into the thalamus via two brain electrodes.
After the initial tests, just 48 hours after surgery, there seemed to be some minor improvement in responses and EEG patterns.
This was a good sign, but because this was a new technique and each patient’s pattern of brain injury is distinct, the researchers had to then begin experimenting with different stimulation patterns.
After 18 weeks of testing, they found what seemed to be the optimal stimulation programme.
The patient showed longer periods of eye-opening and increased responsiveness to command and better limb control. He began to name simple objects, chew his own food and could produce up to six-word sentences.
In terms of the patient’s pre-injury level of functioning, the results are modest, but as an improvement on MCS, largely thought to be untreatable after 12 months, it’s a remarkable achievement.
The researchers note that this might not help all people with MCS, as this patient was specifically chosen because of his ‘widely preserved brain structure’, but, as with a previous treatment for coma we reported it’s more evidence that targeting the arousal system might be key in some cases.
In the same issue of Nature there’s an interesting (but closed access) commentary that makes some interesting points about what this tells us about consciousness, and particularly, the brain’s unconscious decision about when to rouse us into consciousness:
In essence, the brain does not process information in the abstract but instead consults information acquired through the senses and in memory insofar as it bears on the decisions made about potential actions and strategies. Our brains allow us to decide among possible options ‚Äî that is, how and in what context to engage with the world around us. The brain makes many such decisions unconsciously. Indeed, the decision to engage at all is, in effect, an unconscious decision to be conscious. Thus, the brain of the sleeping mother queries the environment for the cry of her newborn. We suspect that the normal unconscious brain monitors the environment for cues that prompt it to decide whether to awaken and engage. This mechanism may be disrupted in various disorders of consciousness, including the minimally conscious state, hypersomnolence, concussion, abulia (lack of will) and possibly severe depression.
Previous theories of consciousness have relied on a central executive and magical physiological phenomena (for example, synchronized reverberations) to elevate the subconscious functions of the brain to consciousness. However, viewed as a decision to engage, consciousness can instead be studied in the same framework as other types of decision and the allocation of attention. Rather than a central executive, there seems to be a network of brain regions that organize the resting state and maintain overall orientation towards context. It is quite possible that they make decisions about whether or not to engage and in what way. They do what Sartre considered impossible: they choose whether to choose or not.
Link to Nature news story on the research (via Retrospectacle).
Link to summary of scientific paper.
Link to Nature commentary.
mp3 of Nature podcast discussion (starts 19 minutes in).
Link to write-up from ABC News.