The Ravenous Brain: How the New Science of Consciousness Explains Our Insatiable Search for Meaning (41 page)

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Authors: Daniel Bor

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It’s important to emphasize in all these studies that, as usual, a negative result on scans is hard to interpret—for instance, if a patient fails to generate the appropriate brain activity, she might just have moved too much in the scanner, which in itself spoils results. However, passing this test clearly reflects consciousness, and as methods are refined, it should become easier both for patients to prove they are aware and for them to communicate.
Although none of these methods are close to being a conventional clinical tool, there is every reason to assume that the situation will change in the next five years or so. Having a standard, brain-based method by which patients could express their thoughts and wishes, despite being completely unable to move a muscle, would give them a much-needed voice and provide hope and reassurance to their anxious families.
CHECKING THE INTEGRITY OF CONSCIOUS NEURAL HIGHWAYS
 
The methods described above essentially seek a lucky glimpse of conscious communication in the peaks and valleys of flittering brain activity. But what if the patient is having a bad day when scanned—for instance, spending much of this time asleep, when in fact he is usually very conscious? Or what if the patient really is only partially conscious, but all the neural architecture is present for a solid recovery? There is certainly mileage in applying less direct neural investigations that bypass questions of online consciousness or communication. Indirect methods with the most potential for these patients include those that examine whether the brain is sufficiently physically wired to support consciousness, or whether regions are still communicating with each other, in a way that reflects awareness. These methods, although less sexy, could nevertheless prove more robust than other techniques that rely on the patient obeying instructions, and they might also offer more reliable predictions of recovery.
And, given the level of maturity of the science of consciousness today, it is certainly possible to exploit existing knowledge about consciousness and the brain in order to make accurate diagnostic tests of PVS.
First, it is well known that the thalamus, that central relay station in the brain, has a critical role in consciousness. Although it might not be as important as the prefrontal parietal network in supporting the richness of our various experiences, its normal functioning, as a means of transmitting and combining information freely throughout the cortex, is necessary for awareness to occur. Significant damage to the thalamus, as seen in anatomical scans, is an obvious indicator that consciousness will be lacking and recovery unlikely. But even if the thalamus seems intact, that doesn’t mean that its connections with the rest of the brain are still functional. So Davinia Fernandez-Espejo, Adrian Owen, and colleagues recently used a relatively novel MRI scanning technique, diffusion tensor imaging, in order to examine how well the thalamus was still connected with other regions in such patients. It turned out that the integrity of these fiber pathways was an excellent diagnostic measure of whether patients were classed as PVS or minimally conscious, securing a 95 percent accuracy. This is a considerably higher success rate than is typically reached by means of standard clinical behavioral assessments, which, you may remember, have a lamentable 43 percent misdiagnosis rate.
Looking directly at the pathways of the prefrontal parietal network is another clear research goal, emerging out of the large bank of evidence arguing that this is the most central set of brain regions for consciousness. Using a complex neuroimaging technique that assesses how one brain region causes activity in another, Melanie Boly and colleagues were able to show that, while in PVS patients the prefrontal cortex was no longer influencing regions toward the back of the brain, in minimally conscious patients and normal subjects there was a more robust, active link between the regions, with information flowing both away from and toward the prefrontal cortex.
Another principled approach, this time springing from information integration theory, uses the TMS-EEG technique mentioned in Chapter 6, where an initial burst of cortical stimulation, initiated by the TMS machine, is then monitored by EEG for its spread and duration. A prolonged bouncing of activity throughout the cortex is found in awake, aware individuals, while only a local, short-lived response is present when we’re in a dreamless sleep. Although this research is in the early stages, the approach is also being used to measure the level of residual awareness in vegetative patients.
THE DIFFICULTY OF REPAIRING HUMPTY DUMPTY
 
Accurately finding ways of judging whether a vegetative patient is conscious is always only half of what’s on the mind of the patient’s loved ones. The family members also want to know if the patient will recover, and whether there are any treatments that will aid the healing process. Here, the news is not so encouraging, although there are a range of potential treatments.
For instance, Nicholas Schiff and colleagues carried out a procedure known as deep brain stimulation on one thirty-eight-year-old patient who had previously been in a minimally conscious state for six years. This technique involves an operation to insert electrodes deep into the brain, and in this case using those wires to continuously stimulate the thalamus for 12 hours each day. In this way, not only was the thalamus reactivated, but so were its many connected regions, including the prefrontal cortex.
Before the surgery, there were only the barest signs of awareness, with the patient occasionally able to follow verbal instructions, but unable to utter a single word himself. Almost immediately after the electrodes were turned on, the patient seemed to wake up far more effectively; he could now keep his eyes open and turn his head toward a spoken voice. This was dramatic in itself, but the patient continued steadily to improve. By the end of the study six months later, he was not only uttering single words for the first time and naming objects, but sometimes even saying short sentences. Whereas before he’d had little motor control and wasn’t even able to chew food, now he could hold a cup to his lips and feed himself three meals a day. These are all remarkable improvements, but it’s important to emphasize that, despite such dramatic progress, the patient was by the end still very ill, a shadow of his former self. It’s also unclear whether this procedure would work at all on PVS patients, who, unlike this man before his operation, show no obvious signs of consciousness.
A different and controversial approach, this time deliberately directed instead to PVS patients, simply involves dosing these patients with medication. Ralf Claus and colleagues have provided provisional evidence that, for some vegetative patients, a common sleeping drug, zolpidem, can paradoxically allow them to wake up for about 4 hours at a time. It’s almost as if their ability to sleep and wake has gone totally askew and this drug may temporarily reset and recalibrate the system. From showing no signs of consciousness beforehand, one PVS patient a few hours after zolpidem was administered could verbally answer questions appropriately and even perform simple calculations. Although other research groups have also shown that zolpidem can indeed improve conscious levels in such patients, it seems that only a small minority, about one in fifteen participants, will have any kind of benefit from the drug.
Occasionally, patients with few signs of consciousness can spontaneously recover on their own, even after years. In one famous case, a man named Terry Wallis suffered from massive brain damage and a coma after being thrown from his pickup truck. A few weeks after the accident, he was judged to be in a minimally conscious state. He remained in this state for nineteen years, until one day, out of the blue, he appeared almost normally conscious. Three days after this, he was already able to speak almost normally. This sounds, on the surface, miraculous, but when you start examining the details, you find that the situation isn’t nearly as encouraging as it at first appeared. Wallis had severe amnesia, poor working memory, an inability to plan or strategize, impulsive behavior, and a changed character, now far less mature than his nineteen-year-old self at the time of the accident. In line with this, his brain scans revealed severe brain shrinkage, even though there was some promising evidence that new pathways were growing, which might have explained why he woke up in the first place.
With all these patients, a good prognosis critically depends on how much brain damage has already occurred and what caused the patient to be in this state in the first place. Returning to the case of Terri Schiavo, despite the hopes and prayers of her parents, her brain shrinkage was so severe that there was, sadly, very little brain left (see
Figure 9
), and certainly no hope that any pill or stimulator would fix her.
For the vast majority of these PVS patients, or indeed anyone who suffers from some form of serious brain damage, probably the best future hope for effective treatment is via some form of stem cell therapy. Theoretically, stem cells injected into the brain could turn into new neurons to reverse the extensive brain damage. At present, though, there are both real dangers to the treatment, with stem cells tending to form tumors, and great difficulties in rebuilding large sections of cortex. And even if, in the decades to come, stem cell therapy did mature and become a viable treatment, it might well be that patients would emerge with most of their old memories, skills, and personalities wiped out from the initial brain damage. They would be disturbingly reborn, with a new consciousness and character to grow, piece by piece. It’s hard to imagine what extra challenges such a patient would face, when even in normal development and in our daily lives we so frequently struggle to find a mentally healthy path through our experiences.
8
 
Consciousness Squeezed, Stretched, and Shrunk
 
Mental Illness as Abnormal Awareness
 
SHARP FRACTURES IN AWARENESS
 
My wife and I have been together for thirteen years. In some ways, because of her fierce emotional warmth, her busy intellect, and the fact that we think alike on many topics, it has been very easy to be with her. In other ways, through absolutely no fault of hers, it has been, on occasion, a struggle. My wife suffers from one of the various forms of bipolar disorder and, like many people plagued by this illness, she endured many exasperating years as the psychiatrists toyed with a sequence of alternative diagnoses before landing on the current label. They then prescribed an even longer sequence of largely ineffective medications, and we reacted to each new drug with the increasingly tired cycle of hope, frustration, and despair.
When my wife is ill, she is usually “down”: She will sleep much of the day, profess to be perpetually lethargic, and be globally, profoundly lacking in motivation—sometimes to such an extent that she can hardly move her body. She can’t make decisions, can’t recall normally vivid memories, and will fail to understand topics that in normal circumstances she’d grasp with ease. She will feel either numb or terribly distraught. Her thoughts and feelings will bend heart-wrenchingly away from rationality. They will converge on the view that she is the most ugly person alive (when in fact she is very good looking), that she is incredibly fat (she has a BMI of about 21), that she is utterly stupid (she holds a PhD in genetics, along with a clutch of other degrees, from both Oxford and Cambridge Universities), and that she is the most unkind, unpopular person in the world (she in fact has a large set of friends, and is very giving toward them).
Far less frequently, she will be “up”: She will sleep little—perhaps skipping bed for a night or two. She will feel high, disinhibited, excited, and easily excitable, almost as if she were drunk. She will have lots of energy and start various new projects, some of which, under normal circumstances, she would think were a complete waste of time. She will make lots of connections between ideas, rather like forming new, insightful chunks, but at their extreme form, the connections will make no sense, and the ideas may be somewhat absurd and, in hindsight, embarrassing.
Of course, illnesses like bipolar disorder are tremendously complex. But I’ve been struck at times by the extent that her symptoms could be explained by a warping of her consciousness. When she’s within a depressive episode, it’s as if there isn’t enough consciousness to go round; she’s perpetually tired, and she lacks the awareness to realize the extreme irrationality of her beliefs about herself. When she’s in a manic episode, it almost seems as if there’s too much consciousness for her brain to cope with; she never gets sleepy, her melting pot of ideas is boiling too hot and bubbling over the rim, and her “innovation machine” of a conscious mind repeatedly spews out spurious insights.
She was prescribed many of the standard drugs for depression and bipolar disorder—for instance, selective serotonin reuptake inhibitors (SSRIs), to raise her mood (by raising her serotonin levels), and mood stabilizers, like lithium (whose effect no one really understands), to keep her on an even keel. Although some of these drugs made her physically very ill, and one or two made her mental health plummet frighteningly, none helped her bipolar symptoms (a somewhat common experience in patients like her). Eventually, we were lucky enough to chance upon a particular stimulant medication. This drug, within a day, removed the bulk of her depressive symptoms. It’s not perfect, and may not be suitable for many other bipolar patients, but it is orders of magnitude better than the more conventional medications she tried and allows her to lead a far more functional life than before.

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