In the brain, when the intensity of the neuronal response to a stimulus exceeds a certain threshold, a second wave of cerebral activity is produced, about 300 milliseconds after the stimulus occurs. This second wave of activity is no longer confined to the brain regions related to the sensory nature of the stimulus (the visual cortex for an image or the auditory cortex for a sound), like a wildfire that has spread throughout the brain.
If this second massive wave takes over the brain almost entirely, the stimulus is conscious. Otherwise, it isn’t. The cerebral activity leaves a mark that is a sort of digital signature of consciousness, allowing us to know if a person is conscious or not, to access their subjectivity, and to know the contents of their mind.
This wave of cerebral activity, which is only registered in conscious processes, is:
(1) MASSIVE. A state of great cerebral activity propagated and distributed throughout the entire brain.
(2) SYNCHRONIZED AND COHERENT. The brain is made up of different modules that carry out specific activities. When a stimulus accesses consciousness, all of these cerebral modules synchronize.
(3) MEDIATED. How does the brain manage to create a state of massive, coordinated activity among modules that usually work independently? What performs that task? The answer is, again, analogous to the social networks. What makes information go viral? On the web there are hubs or traffic centres that function as huge information propagators. For example, if Google prioritizes a particular piece of information in a search, its diffusion increases.
In the brain there are at least three structures that carry out that role:
(a) The frontal cortex, which acts sort of like a control tower.
(b) The parietal cortex, which has the virtue of establishing dynamic route changes between different brain modules, sort of like a railway switch that allows a train to pass from one track to another.
(c) The thalamus, which is in the centre of the brain, connected to all the cortices, and in charge of linking them all. When the thalamus is inhibited, it strongly disassociates traffic in the cerebral network–as if one day Google shut down–and the different modules of the cerebral cortex cannot synchronize themselves, making consciousness vanish.
(4) COMPLEX. The frontal cortex, the parietal cortex and the thalamus allow the different actors within the brain to act in a coherent manner. But how coherent does the activity in the brain have to be in order for it to be effective? If the activity were completely disorganized, the traffic and flow of information between different modules would become impossible. Full synchronicity, on the other hand, is a state in which ranks and hierarchies are lost, and where modules and compartments that can realize specialized functions are not formed. In the extreme states of completely ordered or chaotic cerebral activity, consciousness disappears.
This means that the synchronization must have an intermediate degree of complexity and internal structure. We can understand it with an analogy to musical improvisation; if it is totally disorganized, the result is pure noise; if the music is homogeneous and no instrument offers any variation from the others, all musical richness is lost. What’s most interesting happens at an intermediate degree between those two states, in which there is coherence between the different instruments but also a certain freedom. It is the same with consciousness.
Reading consciousness
In July 2005 a woman had a car accident that left her in a coma. After the routine procedures, including surgery to reduce pressure in the brain caused by various haemorrhages, the days passed with no signs of her recovering consciousness. From that moment on, and over weeks and months, the woman opened her eyes spontaneously, and had cycles of sleep and wakefulness and some reflexes. But she made no gesture that indicated a voluntary response. All these observations corresponded with the diagnosis of a vegetative state. Was it possible that, against all clinical evidence, the patient had a rich mental life, with a subjective landscape similar to that of a person in a state of full consciousness? How could we know? How can we investigate the mental life in someone else’s mind if they can’t communicate their thoughts?
In general, other people’s mental states–happiness, desire, boredom, weariness, nostalgia–are inferred by their gestures and their verbal expression. Language allows us to share, in a more or less rudimentary way, our own private states: love, desire, pain, a special memory or image. But if you are unable to externalize this mental life, as happens for example while sleeping, a person is locked in. Vegetative patients do not externalize their thoughts and, therefore, it was normal to assume that they might not have consciousness. This has all changed. The properties of conscious activity that we enumerated become dramatically relevant because they allow us to decide, in an objective way, whether a person has signatures of consciousness. They work as a tool to read and decipher other people’s mental states, something that becomes more pertinent when it is the only way to do so, such as in the case of vegetative patients.*
Observing the imagination
Some seven months after the car accident that left her in a vegetative state, doctors made a study of the woman using functional magnetic resonance imaging. Can tracing cerebral activity provide a view of her thoughts? Her brain activity, when hearing different phrases, was comparable with that of a healthy person. Most interestingly, the response was more pronounced when the phrase was ambiguous. This suggested that her brain was struggling with that ambiguity, which indicated an elaborate form of thinking. Perhaps the woman wasn’t truly in a vegetative state? The observations of her brain were not enough to respond conclusively to such a significant question. During deep sleep or under anaesthesia–where one presumes that a person is indeed unconscious–the brain also responds elaborately to phrases and sounds. How can the signature of consciousness be more precisely examined?
When a conscious person imagines that they are playing tennis, the part of the brain that activates the most is known as the supplementary motor area (SMA). This region controls muscular movement.* On the other hand, when someone imagines walking through their house–we can all mentally follow a route through many maps, train lines, friends’ grandmothers’ houses, cities, trails–a network activates, which primarily involves the parahippocampus and the parietal cortex.
The regions that activate when someone imagines they are playing tennis are very different from the ones that activate when they imagine walking through their house. This can be used to decipher thought in a rudimentary but effective way. It is no longer necessary to ask someone if they are imagining tennis or imagining moving through their house. It is possible to decode it precisely just by observing their cerebral activity. In effect, we can read someone else’s mind; at least along a binary code of tennis or house. This tool becomes particularly relevant when we cannot ask questions. Or, more accurately, when the person cannot answer them.
Can that 23-year-old vegetative woman imagine? The British neuroscientist Adrian Owen and his colleagues posed that question in the resonator in January 2006. They asked the patient to imagine tennis and then imagine walking around her house, then tennis again, then walking again, and so on, alternately imagining one activity and then the other.
The cerebral activation was indistinguishable from that of a healthy person. So it can be reasonably inferred that she was capable of imagining and, therefore, that she had conscious thoughts that could not have been supposed by her doctors based on clinical observation.
The moment when she managed to break through the opaque shell that had confined her thoughts for months–as Owen and his team observed her thinking directly in her brain–was a landmark in the history of human communication.
Shades of consciousness
The demonstration with tennis and spatial navigation has an even greater significance: it is a way of communicating. A rudimentary but effective one.
With this we can establish a sort of Morse code. Every time you want to say ‘yes’, imagine you are playing tennis. Every time you want to say ‘no�
��, imagine you are walking through your house. In this way, Owen’s group could communicate for the first time with a vegetative patient, who was twenty-nine years old. When they asked him if his father’s name was Alexander, the supplementary motor area activated, indicating that he was imagining tennis and meaning, in this code, a ‘yes’. Then they asked the patient if his father was named Tomás and the parahippocampus activated, indicating spatial navigation and representing a ‘no’ in the code they’d established. They asked him five questions, which he responded to correctly with this method. But he didn’t respond to the sixth.
The researchers argued that perhaps he hadn’t heard the question, or maybe he had fallen asleep. This, of course, is very difficult to determine in a vegetative patient. At the same time, the result shows the infinite potential of this window on to a previously inaccessible world, as well as raising a certain scepticism.
This last statement, as I see it, is a pertinent and necessary warning about a ‘broken link’ in science communication, one that distorts reality. The traces of communication in vegetative patients are promising but still very rudimentary. It is likely that the current limitations can be overcome with improving technology, but it is deceptive to believe–or make others believe–that these measures indicate an awareness that is similar in form or content to that of a normal life. Perhaps it is a much more confused and disordered state, a disintegrated, fragmented mind. How can we know?
Tristán Bekinschtein, a friend and companion in many adventures, and I set out to approach this question. Our approach was somewhat minimalist: we tried to identify the minimum behaviour that defines consciousness. And we found the solution in an experiment that Larry Squire, the great neurobiologist of memory, had done by adapting Pavlov’s classic demonstration.
The experiment works like this: a person watching a film–by Charlie Chaplin–hears a sequence of tones: beep buup beep beep buup… One is high-pitched and the other is low. Each time the low tone* is heard, a second later that person receives a slightly annoying burst of air on to one eyelid.
Close to half of the participants recognized the structure: the low tone was always followed by the puff of air. The other half didn’t learn the relationship; they didn’t discover the rules of the game. They could describe the tones and the bothersome burst of air but didn’t perceive any relationship between them. Only those who consciously described the rules of the game acquired the natural reflex of closing their eyelid after the low-pitched tone, anticipating the air and attenuating its bothersome effect.
Squire’s results seem innocent enough but are actually quite meaningful. This extremely simple procedure establishes a minimal test–a Turing test–for the existence of consciousness. It is the perfect bridge between what we wanted to know–whether vegetative patients have consciousness–and what we could measure–if they blink or not, something that vegetative patients can do–so Tristán and I built that bridge to measure consciousness in vegetative patients.
I remember the moment as one of the few in my scientific career when I felt the giddiness of discovery: Tristán and I were in Paris, and we discovered that a patient was capable of learning just as well as people with full consciousness. Then, by laboriously repeating the procedure, we found that only three out of the thirty-five patients we had examined showed this residual form of consciousness.
We spent many years refining the process in order to explore in further detail how reality is seen from the perspective of a vegetative patient who has traces of consciousness. In order to do so, Tristán adapted the experiment with beeps and puffs of air into a more sophisticated version. This time, the participants had to discover that different words in a single semantic category were preceded by a puff of air. Being fully aware wasn’t enough to learn that relationship; they also had to be able to direct their attention to the words. Which is to say, those who were distracted learned in a much more rudimentary way.
So we were able to question the attention focus of vegetative patients and we found that their way of learning was very similar to that of distracted people. Perhaps this is a better metaphor for the functioning of the minds of some vegetative patients with signs of consciousness: flightier ways of thinking, in a much more fluctuating, less attentive and more disordered state.
Consciousness has many signatures. These can be naturally combined in order to determine whether a person has consciousness, but the argument for or against the determination of a patient’s consciousness can never be definitive or certain. If their frontal and thalamic activity is normal, if their cerebral activity has an intermediate range of coherence, if certain stimuli generate synchronous activity and after about 300 milliseconds produce a massive wave of cerebral activity, and if, in addition, there is a trail of directed imagination and forms of learning that require consciousness–if all of these conditions are simultaneously found, then it is very plausible that the patient has consciousness. If only some of them exist, then there is less certainty. All these tools in conjunction are the best means we have today of coming up with an objective diagnosis of conscious activity.
Do babies have consciousness?
Research into others’ thoughts is also a window into the mysterious universe of newborns’ thinking. How does consciousness develop before a child can express it in gestures and concise words?*
Newborns have a much more sophisticated and abstract thought organization than we imagine. They are able to form numerical and moral concepts, as we saw in Chapter 1. But these ways of thinking could be unconscious and don’t tell us much about the subjective experience during development. Are babies consciously aware of what is happening to them, of their memories, their loved ones, or their sadness? Or do they merely express reflexes and unconscious thinking?
This is a very new field of investigation. And it was my friend and colleague of many years Ghislaine Dehaene-Lambertz who took the first stab at it. The strategy is simple; it involves observing whether babies’ brain activity has the cerebral signatures that indicate conscious thought in adults. The trick is very similar to the experiment to understand how, in the adult brain, a conscious process diverges from an unconscious one.
At five months old, the first phase of cerebral response is practically established. This phase codifies visual stimuli, independently of whether they access consciousness. At this point, the visual cortex is already able to recognize faces and does so in similar ways and at a similar speed as adults do.
The second wave–exclusive of conscious perception–changes during development. At one year of life it is already practically consolidated and presents very similar forms to an adult’s but with a revealing exception: it is much slower. Instead of at 300 milliseconds, it consolidates almost a second after seeing a face, as if babies’ conscious film had a slight lag, like when we watch a game being broadcast with a delay and we hear our neighbours shouting ‘goal’ before we see it.
This lag in response is much more exaggerated in five-month-old babies. Long before developing use of speech, before crawling, when they can barely sit up, babies already have cerebral activity denoting an abrupt and extended response throughout the brain, which persists after the stimulus disappears.
It is the best proof we have for supposing that they have consciousness of the visual world. Surely less anchored to precise images, probably more confused, slower and hesitant, but consciousness nonetheless. Or at least that is what their brains tell us.
This is the first approximation in science to navigating a previously completely unknown territory: babies’ subjective thought. Not what they are able to do, respond to, observe or remember, but something much more private and opaque, that which they are able to perceive from their conscious minds.
Deciding on the state of consciousness of a baby or a person in a vegetative state is no longer merely deliberating intuitions. Today we have tools that allow us to enter–live and direct–into the factory of thought. These tools allow us to break through one of the most hermet
ic and opaque barriers of solitude.
Today we still know very little about the material substratum of consciousness, as was the case before with the physics of heat. But what’s most striking is that despite so much ignorance we can today manipulate consciousness: turn it on and off, read it and recognize it.
CHAPTER FOUR
Voyages of consciousness
(or consciousness tripping)
What happens in the brain as we dream; is it possible for us to decipher, control and manipulate our dreams?
Altered states of consciousness
They are both lying down. He is telling her a story he’s told her a thousand times, in a low, monotone voice. He pushes out the air that makes his vocal cords vibrate. The sound is modulated by his tongue, lips and palate. In less than a thousandth of a second, that wave of sound pressure bounces in his daughter’s ear. The sound again becomes movement in her eardrum. That movement activates some mechanical receptors at the tip of the hair cells, a magnificent piece of biological machinery that converts the vibrations of the air into electrical pulses. Each swing of those cells opens up microscopic channels in the membranes through which ions slip in and generate a current that spreads throughout the auditory cortex, and this neuronal activity encodes the words that she, as always, repeats in a whisper. The same words that sound in her father’s deep, monotone voice with delicate inflections now live in the narrative she constructs in her mind when she hears the story that she has already heard a thousand times before.
The Secret Life of the Mind Page 13
