We Are Our Brains (32 page)

Depth electrodes have also recently been used to treat obsessive-compulsive disorder, a condition that causes people to perform certain actions compulsively, like washing their hands hundreds of times a day or pulling out their hair. They become fearful if they don't give in to their obsessions, rendering a normal social life impossible. Since performing compulsive actions makes people with OCD feel good, it's thought that the brain's reward system is involved. The good feeling is caused by the release of the chemical messenger dopamine in the nucleus accumbens (
fig. 16
). Research by Damiaan Denys shows that when traditional treatments fail, patients can benefit from electrodes on both sides of the nucleus accumbens. The theory is that stimulating the region causes dopamine to be released, creating the same reward as the compulsive behavior. As a result, compulsive hand washing can be reduced from ten hours a day to fifteen minutes a day, allowing patients to lead a normal life again. One patient who was successfully cured of compulsive behavior ended up thinking obsessively of sex instead. The electrode turned out to be close to the bed nucleus of the stria terminalis (
figs. 10
and
11
). Whether this was really the cause of the obsessive thoughts has yet to be established.

Along with new breakthroughs, new side effects of depth electrode treatment are also being reported, as in the treatment for tinnitus, which sometimes affects people who are hard of hearing. Because their brain isn't receiving normal auditory information, it starts to produce its own sound sensations, causing some people to hear constant music (see
chapter 10
). Stimulating the part of the brain that stopped receiving auditory information would seem a logical way of curing this condition. However, a patient who was treated for tinnitus with depth electrodes in the temporal cortex (
fig. 28
) not only continued to hear the annoying tunes but also had an out-of-body experience as a side effect. He felt as if he was standing a couple of feet to the left of and behind his body (see
chapter 7
).

FIGURE 23.
The depth electrode (E) was inserted at the correct location in the subthalamic nucleus of the brain of a Parkinson's patient. T = thalamus, OT = optical tract.

Another unexpected side effect occurred in the case of a man who'd had depth electrodes implanted in his hypothalamus to inhibit his binge eating. He was so obese that he didn't even fit into the scanner. Stimulation from the electrode didn't help him to lose weight, because he had a tendency to switch it off at night so that he could eat. But when it was on, he suddenly experienced events that had taken place thirty years earlier, like walking through the woods with friends. Each time he could remember more and more details. This side effect seemed to be due to activation of the temporal lobe. Episodic memories of this type also occur when people see their lives flash past in near-death experiences (see
chapter 16
). The temporal lobe is important for memory, and since stimulation has been shown to improve memory, studies are now under way to see if it can be used to help patients with memory problems. So this technique not only appears to have great clinical potential, but it can also teach us a great deal about how our brains work by showing us what happens when depth electrodes aren't quite in the right place.

I was once told by Ruut Veenhoven, a professor of “social conditions for human happiness,” that happiness doesn't depend on having a goal in life. That didn't surprise me at all, given that life came into being and evolved by accident and has no purpose. But enjoying life is useful because it's closely connected to eating and reproducing and therefore promotes survival. Indeed, the pursuit of pleasure is such a strong impulse that it causes overpopulation and obesity. Positive emotions like falling in love, maternal love, and pleasure in social contacts also benefit the survival of the species.

Human cognitive development has enabled feelings of pleasure to
be elevated to the “higher” orders of art and science, altruism, finance, and transcendent activities, culminating in happiness. Happiness is contagious. When someone is happy, their friends, partners, and family are more likely to be happy.

Positive feelings can also be disturbed, as in the case of some psychiatric patients. Mania can go hand in hand with intense happiness. Conversely, anhedonia, the absence of any feeling of pleasure, is a characteristic of depression and is associated with schizophrenia, autism, and addiction. The ventral striatum plays a crucial role here. Parkinson's patients with lesions in that area sometimes suffer from flat affect (lack of emotional expression) or even anhedonia. The increased levels of corticosteroids associated with depression inhibit dopamine release in the ventral striatum, thus apparently blocking all pleasurable feelings. Conversely, stimulation of the area can alleviate depression.

Feelings of pleasure and happiness are linked to activity changes in a great many areas of the brain. Activity in the prefrontal cortex increases in response to both tasty food and financial reward. This area also controls whether or not you give in to temptation. But the prefrontal cortex is not where pleasure is
generated.
Patients who have undergone leukotomy, an operation in which the prefrontal cortex is disabled, can still derive pleasure from food and sex. The pleasurable feeling is generated in reward systems located lower down in the brain.

Addictive substances make use of existing brain systems to induce pleasurable feelings. Sigmund Freud took cocaine for a while, writing in 1895 that the feelings the drug generated couldn't be distinguished from normal feelings of well-being. Tests in which laboratory animals were given small amounts of opiates in the areas of the brain that are considered “hedonistic hotspots” show that those brain structures are
sufficient
to induce pleasurable feelings. However, it's only possible to say whether an area is
necessary
for pleasurable feelings if the feelings disappear when the area is disabled. Similarly, stimulating a brain area (the ventral striatum or nucleus
accumbens) is
sufficient
to create a rewarding effect, but disabling the area does very little to impair the rewarding effect of food, showing that it isn't
necessary
for the creation of such an effect. Our taste for sweet food depends on a single hedonistic hotspot at the base of the brain. Disabling that area makes sweet food taste repellent. Likewise, the hypothalamus is necessary for infatuation, maternal love, and pair forming. The other brain areas that show changes of activity in response to pleasure or happiness aren't necessary for the pleasurable feeling, but they are necessary for processes linked to it, like learning, memory, decision-making, or behavioral effects. The dopamine reward system is involved in anticipatory pleasure, motivation, and attention relating to enjoyment. When someone is clinically depressed, the stress hormone cortisol inhibits the dopamine reward system, preventing them from feeling pleasure. Cocaine, on the other hand, extends dopamine's availability to receptor cells in the brain. The brain's own opiates are also involved in the sensation of happiness. Oxytocin and vasopressin play a role in infatuation, orgasm, pair forming, and maternal love. Deficiencies in those two chemical messengers are associated with autism.

Some people can generate feelings of happiness themselves. Brain scans of nuns instructed to reexperience their ecstatic love of God showed changes of activity in reward structures. A brain tumor in the temporal lobe can also generate ecstatic experiences, for instance the feeling of direct contact with Jesus. The ecstatic experiences cease when such tumors are removed.

Alas, it is impossible to induce extreme happiness by means of a stimulation electrode in a single brain location, but there are “self-stimulation hotspots.” Rats with stimulation electrodes placed in certain areas of their brains can be stimulated to eat, drink, and have sex many times in the space of a minute. But whether they actually enjoy it is debatable, given the findings emerging from stimulation studies of humans. One young man who'd had an electrode implanted in the accumbens/septum region constantly engaged in self-stimulation. He protested vehemently when the electrode was
removed. It had induced feelings of alertness, warmth, arousal, and an urge to masturbate, but never orgasm or clear evidence of pleasure. A young woman who stimulated herself constantly while experiencing erotic sensations never brought herself to orgasm. Moreover, the constant stimulation led her to neglect herself. It seemed as if she, too, wasn't experiencing any kind of real pleasure. So for the time being we'll have to rely on the old-fashioned method of obtaining pleasure and happiness. And there's nothing wrong with that.

The brain gets information from the outside world through the senses and then takes action by means of motor control. Until recently, if you lost one of your senses you were doomed to be blind or deaf or, if your spinal cord was damaged, to be paralyzed for life. At the Netherlands Institute for Neuroscience's International Summer School of Brain Research in 2008, however, new developments in brain computer interfaces or neuroprostheses appeared to offer future hope of returning sight to blind people and enabling paraplegics to walk again. By far the greatest advances are being made in the field of hearing. Since 1960, bionic ears in the form of cochlear implants have been implanted in patients whose deafness is caused by an inner ear disorder. The implants stimulate the nerve cells connected to the nonfunctioning hair cells in the inner ear. Since 1980 it has been possible to augment this technique by implanting twenty-two electrodes, and over a hundred thousand people with cochlear implants are now able to hear surprisingly well or even normally. However, implants do not work when deafness is due to failure of the auditory nerve. Deafness of that sort has been successfully
treated by implanting twelve electrodes in the brain stem (rather than in the inner ear), enabling auditory information to reach the brain, thus improving communication.

Millions of people around the world are blind because the light-sensitive cells in their retinas, the photoreceptors, have been destroyed. Gerald Chader, an ophthalmologist from Los Angeles, described experiments with three such patients who were totally blind. Information was sent from a tiny camera on a pair of spectacles to a miniature receiver that had been attached to the patients' retinas during an operation. A microprocessor translated the visual signals into electronic signals. Sixteen electrodes made contact with the layer of nerve cells in the retina that was still intact, which passed on the information to the brain via the optic nerve. After considerable training, the patients could distinguish between objects such as a cup and a plate. The number of electrodes is being gradually increased to one thousand; with any luck facial recognition will become possible within five to ten years. In a study by another research group, the miniature camera transmitted visual information to a device in the patient's pocket, where it was electronically processed and then sent to a receiver connected to a large number of micro-electrodes implanted in the visual cortex (
fig. 22
).

It is increasingly possible to determine from the electrical activity of large numbers of cells in the motor cortex what motion they intend on carrying out, making it feasible to control a prosthetic arm, for instance. Such advances also open up possibilities for the future treatment of paraplegia. Paraplegic animal studies show that electrical stimulation of the spinal cord, three months of training, and supporting medication can generate a walking pattern that isn't directed by the brain. Gregoire Courtine of Zurich estimates that within five years' time he'll be able to use this approach to treat patients. A spectacular experimental result was obtained in the case of twenty-five-year-old Matthew Nagle, who was left fully paralyzed after being stabbed in the neck with a knife. A 4-by-4-millimeter plate with ninety-six electrodes was implanted in his motor cortex (
fig. 22
).
When connected to a computer, the plate created an interface powered by signals from the cells controlling his motor system. He was able to use the computer after just a couple of minutes, moving a cursor on the screen by simply imagining the action. He could draw a circle on the screen, read his email, play computer games, and even open and close a prosthetic hand. But this experiment, besides revealing the potential of a neuroprosthesis, also showed its limitations. Before the operation, Nagle had been able to operate a computer using speech recognition. After the operation he was hooked up to a large computer, with an assistant always standing behind him. As a result, the added value of the implanted electrodes wasn't great. So when the electric signal from his brain decreased after about nine months, he decided to have the electrodes removed. A great deal still needs to be done, but there are certainly many hopeful advances being made in this field of research.