We Are Our Brains (25 page)

A series of spectacular observations was made by researchers from Cambridge and Liège using fMRI, starting with a twenty-three-year-old woman who had been in a vegetative state for five months following a traffic accident. Under the circumstances her brain was remarkably undamaged. When someone spoke to her, her middle and superior temporal gyrus (part of the temporal lobe,
fig. 22
) would show normal activation. Ambiguous sentences caused Broca's area (language processing,
fig. 8
) to light up. When asked to “visit” all the rooms in her house in her mind, activity was seen in the parts of the brain that control spatial orientation and locomotion: the parahippocampal gyrus (
fig. 26
), the parietal cortex (
fig. 1
), and the lateral premotor cortex (
fig. 22
). When instructed to play tennis, the area for motor coordination (supplementary motor area) lit up. A study was then carried out of fifty-four comatose individuals who had sustained severe brain damage (thirty-one of whom were in
a minimally conscious state). In five cases, appropriate responses were shown to commands. Four of these individuals were in a vegetative state. Although changing activity patterns appeared to show that they were aware of themselves and their surroundings, one wonders to what extent one can really speak of “consciousness” in such a situation. A subsequent experiment involved asking one vegetative patient, a twenty-nine-year-old man, simple questions like “Is your father named Thomas?” or “Do you have brothers?” He was asked to think of one type of activity if the answer was yes, and another type of activity (giving a different brain image) if it was no. The different patterns of brain activity showed his answers to be correct in five out of six questions. His responses revealed that he must have at least retained a residual degree of higher brain function, like cognition. But whether these experiments show a form of consciousness in which you're aware of your own situation, for which communication between intact brain areas is essential, remains unclear. And says nothing of whether the patient would wish to continue living in such a situation.

“Absence seizures” are a form of epileptic seizure in which there's a break in consciousness for around five to ten seconds. During that time, patients look blank and don't respond. They often blink their eyes and smack their lips. Their awareness is impaired, and their frontoparietal networks (
fig. 1
), crucial to consciousness, are much less active. In complex partial seizures, sometimes lasting several minutes, consciousness is also impaired. Patients are awake but can no longer respond. They make automatic movements with their hands and mouths, and frontoparietal activity is again much reduced. These changes in activity in the cerebral cortex aren't found in patients with temporal lobe epilepsy whose consciousness isn't impaired (see
chapter 15
).

Indeed, the distinction between a vegetative state and minimal consciousness revolves around the functioning of the frontoparietal network. In the former case, the network is disconnected. In the latter, speech and complex auditory stimuli do spark general activity of
the network that is crucial to consciousness, as shown in fMRI and PET studies. This also means that in principle, an entire network can be recruited in these patients, as was shown in the case of the minimally conscious man who was aroused when his thalamus was electrically stimulated using brain electrodes. It's claimed that music or electrical stimulation of a nerve in the arm (the median nerve) can speed up the process of reviving someone from a state of minimal consciousness, but very few controlled studies have been done, and so far there have been no spectacular results.

For self-consciousness you need a combination of sensory input and an intact cerebral cortex. The premotor cortex is important for the feeling that a certain body part belongs to us. It is there that various types of sensory information, like input from eyes, ears, organs of balance, muscles, tendons, and joints (proprioception) and the sense of touch are put together. You can fool your premotor cortex with the following little trick. Put a rubber hand on the table where your own hand would be, meanwhile putting your hand under the table where you can no longer see it. If someone then repeatedly strokes the rubber hand and your own hand at the same time, your brain combines the sight of the rubber hand being stroked with the sensation of your real hand being stroked. After about ten seconds you begin to regard the fake hand as your real one. If someone suddenly hits the rubber hand with a hammer you jump out of your skin. It seems that the combination of touch (coming from your own, hidden hand) and visual information (coming from the fake hand) is needed for the illusion that this is your real hand. Scans of people
experiencing this illusion show activity in the premotor cortex and cerebellum. The feeling that a body part belongs to you appears to be based on nothing more than the activity of the few groups of neurons in a few very specific brain areas.

Self-consciousness can be impaired or lost for various reasons. In the first stage of Alzheimer's, around 10 percent of patients aren't aware of their degeneration. The percentage increases as the disease progresses. This unawareness that something is wrong with you is called anosognosia (from the Greek
nosos
, “disease,” and
gnosein
, “to know”). It's usually the person's partner who notices that something is wrong and makes them see a doctor. Anosognosia is linked to reduced activity in the angular gyrus, near the upper edge of the temporal lobe (
fig. 28
). It's here that sensory information from the body and the surroundings is combined, making this area essential for self-consciousness. This part of the cerebral cortex is increasingly damaged as Alzheimer's progresses.

Out-of-body experiences or near-death experiences (see
chapter 16
) are also caused by a malfunction in the angular gyrus. A lack of oxygen prevents the angular gyrus from integrating the sensory information coming from your body, including the organs of balance, disrupting consciousness of your entire body.

Building on the rubber hand experiment, the Swedish scientist Henrik Ehrsson induced out-of-body experiences in experiments using cameras linked to a head-mounted video display. The participants were given goggles with a video screen for each eye. The screens showed images from two cameras filming them from behind, so that participants saw a 3-D image of their own back. Ehrsson then used two plastic rods to simultaneously touch a participant's actual chest and the chest of the virtual body, moving the second rod to where the virtual chest would be according to the camera pictures. This gave participants the illusion that they were in the virtual body, and made their own body appear to be someone else's. When the virtual body was threatened with a hammer, the participants reacted as if the threat were real. Their fearful attempts to ward off the
blow were accompanied by physiological responses (notably the level of perspiration on the skin), showing that their emotions were aroused. In Switzerland, Olaf Blankes carried out similar experiments in which participants watched holographic projections of their own bodies. Afterward he blindfolded them and asked them to walk back to the spot where they had been standing. Participants who had had an out-of-body experience during the experiment walked back to the spot where their virtual bodies had stood. So self-consciousness isn't a metaphysical construct. Your brain constantly manufactures the sense that your body belongs to you, using sensory information from muscles, joints, vision, and sensation.

Methods of fooling consciousness can also be used to treat patients with chronic phantom pain, for instance after having had an arm or leg amputated. The neuroscientist V. S. Ramachandran discovered that phantom pain is caused by a conflict in the brain. Each
time a patient wants, say, to move their (amputated) hand, they receive a signal back that it is impossible. As a result, the brain ultimately forces the phantom hand into an extremely painful, cramped position. Ramachandran's solution was as brilliant as it was simple. He placed a mirror perpendicular to his patients' chests, between their two hands, so that when they stretched out their normal hand and viewed the mirror from that side, it appeared as though both hands were working. The patients were given exercises in which they calmly opened and closed their normal hand while looking at their “phantom hand” in the mirror. Although they knew that it was an illusion, the visual input of a relaxed, calmly moving hand helped their phantom hand to relax and the phantom pain to disappear. One man whose leg had been amputated had been unable to wear his leg prosthesis for eight years due to phantom pain in his stump. After a mere three to four hours of mirror therapy, his pain had gone, and he was able to practice walking on his prosthetic leg for the first time, even though he knew that the leg he had seen move in the mirror no longer existed.

FIGURE 22.
Some specialized cortical areas. (1) Primary sensory cortex, (2) auditory cortex, (3) motor cortex, (4) visual cortex. Also: (5) middle temporal gyrus, (6) superior temporal gyrus, and (7) premotor cortex.

Alien hand syndrome (see
chapter 17
) shows that self-consciousness also requires effective communication between the left and right hemispheres of the brain. This syndrome can occur if the bundle of fibers connecting the two (corpus callosum,
fig. 2
) is damaged. Sometimes surgeons have even deliberately severed this link in a last-ditch attempt to make life bearable for patients with disabling epileptic seizures. After the operation, these patients turned out to have split consciousness. The neurobiologist and Nobel laureate Roger Sperry discovered that one side of the brain wasn't aware of what
the other side was seeing. In an experiment, patients could describe only images that reached the left side of the brain, because the ability to speak is located on that side. However, they seemed unaware of images that reached only the right side of the brain. Yet if they were asked to use their left hand (controlled by the right side of the brain) to indicate the image that had just been shown to the right side of the brain, they could do so. So on an unconscious level they had access to information that reached the right side. The left side of the brain then made up a story combining the information from both sides of the brain. The story was logical to the patients but completely incomprehensible to their surroundings. When the right side of the brain registered a written instruction to stand up and walk away, a patient obeyed. When asked why he did so, he didn't say, “You just asked me to,” because he hadn't consciously registered the instruction. So he made up a reason to explain his behavior: “I'm just going to get some hot chocolate.”

The peculiar situation in which a neglect patient finds himself is also often made “plausible” with a great deal of inventiveness and imagination. A paralyzed patient accounted for her situation as follows: “I'd like to get up, but my doctor won't allow me” (see
chapter 7
). In fact these kinds of fantasies are based on a very general principle. If the brain doesn't receive the right information in the expected place, the cerebral cortex at that location will work harder to fill in the gap. Such inventions are perceived as real information (see
chapter 10
). This phenomenon can also arise when there's a lack of auditory information, causing people to hear songs nonstop, or of visual information, causing them to see nonexistent objects in dim light. Lack of memory information resulting from alcohol abuse can lead people to make up events constantly without being aware of it, and lack of information from limbs as a result of amputation can cause phantom pain (see
chapter 10
). Each brain function has its own local system that enables consciousness (
fig. 22
). It's due to the differences in the location of increased cortical activity that we “see” things when we lack visual input and “hear” music when we lack auditory input.

The phenomenon of “blindsight” demonstrates the importance of information following the right route to the right part of the cortex. It was always thought that damage to the left primary visual cortex (
fig. 22
) would result in total blindness of the right field of vision and the other way around. But when individuals who were perceptually blind in a certain area of their visual field had to guess where a light stimulus was located in that area, they were able to do so correctly to an extent that couldn't be due to chance. Seeing something without being aware of it is referred to as type I blindsight, or attention blindsight. It was assumed that this unconscious mode of seeing was due to the receipt of visual information in subcortical areas. A new scanning method showing nerve pathways (diffusion tensor imaging) has revealed that individuals with this form of blindsight do receive information in the part of the cerebral cortex where visual information is processed but that it arrives via an abnormal route through the brain. So even though information arrives in the part of the cerebral cortex where it's normally received, a patient with blindsight isn't conscious of it, apparently because it travels by an unusual route. This would also explain why neglect patients can see something but not be conscious of it, because the information arrives in the cortex by another route, as a result of the damage caused by their stroke.