In a coma or awake?: measuring consciousness is not easy

The health personnel told them that María did not feel pain. But how could they know what was going on in her brain without her being able to communicate? Can current medicine predict whether someone is able to come out of a coma?

Be aware and be aware

Humans – and all animals – go through at least two states of consciousness cyclically: we are alternately asleep and awake. Consciousness can be understood as a continuum that includes being awake, but also the different phases of sleep, states induced by anesthesia and coma.

When animals are awake, we are not only alert, but our consciousness is filled with content. This content refers to our subjective experience, which encompasses both external perception (perceiving the different color tones of a sunset) and internal perception (the experience of pain itself).

Although part of that perception is conscious, a large part occurs unconsciously and we cannot report it.

Detecting consciousness is not easy

Various brain injuries can produce a serious alteration in consciousness known as a coma, which is characterized by people not responding to external stimulation.

After a while, patients can recover sleep-wake rhythms (which we can determine thanks to the encephalographic recording) and even open and close their eyes, although they continue not to respond to external sensory stimulation. This prolonged state of unconsciousness is known as unresponsive wakefulness syndrome.

Sometimes, the condition of these patients improves and progresses to what is known as a state of minimal consciousness. This is diagnosed when patients can respond to simple commands, including providing yes or no responses, present unintelligible speech, or perform purposeful voluntary movements. But they are variable responses and not always reproducible.

Clinically, it is important to detect the state of minimal consciousness as soon as possible, since these patients have a better chance of regaining consciousness. However, detecting the state of minimal consciousness is not easy, and sometimes months – or even years – pass without health professionals detecting it.

MRI can help detect the state of minimal consciousness, as a 2006 study showed. The authors knew that the brain activity of healthy people differs if they are asked to imagine that they are playing tennis (in which case areas of the brain are activated). motor and premotor parts of the brain) or moving around your home (in which case brain regions related to spatial navigation are activated). When they put a person with unresponsive wake syndrome into the scanner, they discovered that she activated exactly those same brain areas. That is, despite her unconscious state, she was able to understand the task instructions and follow them to produce a complex brain response.

Since then, there have been numerous experimental studies that strive to detect brain responses in people with unresponsive wakefulness syndrome. And thanks to the recent contributions of artificial intelligence applied to neuroscience, it has been possible to predict with a level of precision above 77% whether a person will regain consciousness or not.

Beyond diagnosis, these advances allow rehabilitation efforts to be focused on these patients.

Captivity syndrome

Another essential clinical challenge is identifying patients with a syndrome known as locked-in syndrome. Those affected can easily be confused with patients with unresponsive wakefulness syndrome or with patients in a state of minimal consciousness. They are paralyzed at the motor level, being able only to blink and move their eyes vertically. However, they are fully aware of everything that is happening around them and their own bodily sensations.

A follow-up of 44 of these patients showed that the average time it took to diagnose this syndrome was… 78 days! And it was mainly family members, and not health personnel, who raised the alarm.

Measuring the contents of consciousness

If detecting a person’s state of consciousness is a complex task, it is even more complex to determine what exactly they perceive, and what their conscious experience is. In the case of humans, the use of language helps us understand part of their conscious experience. But in studies with non-verbal humans (infants or people with language impairments) and non-human animals we must be able to measure conscious experience without the need for verbal responses.

At the current moment we can determine whether something was perceived or not, how similar are the brain representations that are created when perceiving two objects, or how sure humans or some animal species are of our perception (what is known as metacognition). .

To demonstrate the existence of these metacognitive processes in other animal species, a group of bees have been trained in the laboratory to respond to stimuli that are easy and complex to perceive. If the bees responded correctly, they were reinforced with an appetizing juice (sucrose); If not, they were punished with an aversive substance (quinine). They also had the option of leaving the room and not responding.

Interestingly, it was observed that bees more often chose to leave when the stimuli were difficult to perceive. These data indicate that bees can evaluate the results of their actions, a metacognitive ability that until a few years ago was attributed only to humans (and other species that we have considered “superior” such as primates). However, we are still far from being able to understand what it feels like to be a bee or a mouse.

Scientific advances in the detection of conscious states have been impressive in recent years, but they have not yet reached clinical practice. Detecting states of consciousness, as well as understanding how the brain activity of humans and other animal species gives rise to our subjective experience, is a great challenge. Another current challenge is to create these subjective experiences in artificial intelligence, although it is important to discuss the ethical and practical implications of these future scientific advances that are a little less distant every day.

This article has been published in ‘The conversation‘.