Anna had been depressed for much of her adult life, seeking a range of treatments that might help her condition. She took anti-depressants, underwent psychotherapy and even experienced electroconvulsive therapy – which involves passing electricity through the whole brain. 

Treatments like these were only effective for short periods, and her depression would soon return. Another issue she faced was that she was morbidly obese, weighing 183kg with a BMI of 63 at her heaviest. This resulted in severely limited mobility which, naturally, exacerbated her depression, putting in place a vicious circle of poor health.

In some rare cases, the brain can be de-tuned from debilitating behaviours

Gastric bypass surgery helped her lose some weight but not as much as expected from such a procedure, and it had little impact on her depression. As a last resort treatment, psychiatrists took a drastic decision to implant an electrical device in her brain, an invasive therapy known as deep brain stimulation. It’s a treatment that’s already frequently used to alleviate the symptoms of Parkinson’s disease and epilepsy.

Not only did this treatment significantly help her depression, it had another astonishing outcome – she lost more weight than she had with any previous treatment, losing almost 50% more weight (2.8kg or 6.1lbs) per month than she had done after the gastric bypass surgery. Thomas Munte a neurologist at the University of Lubeck, in Germany, who treated Anna, says that while the initial goal was to treat her depression, the weight loss was the “secondary target” of the surgery. In her case, the two were seemingly linked.

That Anna successfully lost weight following the treatment is opening up new discussions about how to tackle what we know is a world-wide epidemic. It is also is revealing that in some rare cases, the brain can be “de-tuned” from debilitating behaviours, like addiction.

Deep brain stimulating remains controversial but it is not a new treatment. It dates back to the 1930s when neurosurgeons were not nearly as cautious as they are today. It was the neurosurgeon Wilder Penfield who first developed a daring technique for treating epilepsy. He would stimulate different parts of the brain with an electrical probe, keeping patients awake during the process to understand the effect. The idea was that that the brain area causing an issue could be identified and destroyed.

In fact, scientists would essentially “cook parts of the brain”, says Munte, to create small lesions. This was also done to rid individuals of movement disorders like dystonia, which causes repetitive twitching or tremors. It was called “stereotactic surgery” and was dubbed “a period of unrivalled empirical human experimentation”.

At a similar time, a neurologist called Antonio Egas Moniz was busy removing small parts of his patients’ brains in an attempt to rid them of psychological disorders, including depression. He would remove parts of a patient’s frontal lobe – an area vital for forward planning and personality. The treatment was considered successful in several cases – and the inevitable consequences and personality changes were deemed necessary side-effects. Surprisingly, this work gave him a Nobel Prize in 1949. Removing parts of the brain and then observing the results served a useful purpose for the study and practice of brain stimulation – it allowed neurologists to understand which brain areas might benefit from electrodes.

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When antipsychotic and antidepressant drugs became more commonly prescribed, the prevalence of these invasive, irreversible techniques reduced, but the lessons learnt for the brain areas involved would become important for deep brain stimulation as we know it today.

In 2002, deep brain stimulation was approved to treat Parkinson’s disease. It has been extremely effective and more than 40,000 patients have now been treated. Though it’s largely used for tremor disorders, this heralded its use in the treatment of other conditions, such a severe depression in the case of patients like Anna. To perform deep brain stimulation, first scientists use a drill to put a burr hole in a patient’s skull. After that, they place electrodes onto the brain itself. The patient is often awake, enabling researchers to test the specific area while the brain is stimulated.

In Anna’s case the target area for stimulation was the nucleus accumbens, which is part of the brain’s reward centre and an important area for processing pleasure. The area has been linked to depression – as depressed individuals show a reduced interest in pleasure. “You can observe an emotional response by a patient when you are stimulating [this area],” explains Munte, who spoke to BBC Future about his patient, as she wishes to remain anonymous. His analysis was written up in the journal Neurocase.

Treating obesity

Obesity in some individuals, can be due to an altered reward system in the brain, says Munte. Some obese people even show differing brain patterns when exposed to pictures of delectable-looking food than do thinner people. The theory is that the nucleus accumbens is the area that draws addicted people to the object of their desire, be it food, alcohol or drugs. Usually the area of our brain that helps us act rationally prevents the impulsive immediate-reward-hungry part our brain from taking over. But our reward system can, at times “overtake our good manners,” says neurosurgeon Piotr Zielinski, of the University of Physical Education and Sport in Gdansk, Poland. The diet industry flourishes thanks to our nucleus accumbens, he says.

The addictive power of our brain’s reward system was highlighted by a famous 1950s study of rats. They were more inclined to stimulate this brain area than to eat or drink. If this brain area is “disturbed” or perhaps even inhibited (stopped) by electrical stimulation, then the “motivational magnet is no longer there and you’re not drawn to this object,” says Munte.

Sometimes in medicine you start doing [clinical treatments] before you even know exactly how it works

That brain stimulation inhibits an area of the brain from performing its function is still a theory, but one that is strengthened by research in animals. For instance, a study using rats found that brain simulation resulted in an increase of the brain’s inhibitory chemical, gaba, which is released when certain areas need to be constrained. Another study showed that individuals which are better at controlling unwanted thoughts, had more of this chemical.

We still don’t know precisely the impact of brain stimulation and that is one of the reasons why it remains controversial. “Sometimes in medicine you start doing [clinical treatments] before you even know exactly how it works,” says Munte. And for good reason, for Parkinson’s disease, deep brain stimulation has proven to have a much greater impact on quality of life than other treatments.

We may soon see similarly positive impacts for depression and even obesity, now that other promising cases, similar to Anna’s, are emerging. For instance, Zielinski has seen the practice broadened out from treating only Parkinson’s – his department has performed over 2,500 procedures since the 1990s – to also treating pathological aggression, Tourette’s syndrome and obsessive compulsive disorder.

She ceased to steal food from her parents' locked fridge

He has now also treated three people with obesity using deep brain stimulation, all as a last-resort measure when no other technique was lastingly effective. Similarly to Anna, obesity was treated as a compulsive disorder. One patient’s obesity was attributed to a childhood tumour that damaged an area of her brain important for regulating hunger and feeling full.

This patient’s thoughts were completely fixated on food. “Therefore we assumed that bariatric surgery was not a solution,” explains Zielinski. Although her resulting weight loss was not dramatic, the impact it had was life-changing. Brain stimulation has enabled her to live independently. She can now study and “think about anything other than food,” he says. “She ceased to steal food from her parents' locked fridge.”

Addicted brain

Still, Munte stresses that are far from using brain stimulation as a widespread treatment for obesity, especially as it should be considered a last-resort approach. It is an expensive, invasive technique, so is clearly not suitable for the majority of individuals with obesity.

Conventional weight loss programmes rarely produce lasting effects

It is most suited for the subset of obese patients who show addictive-like tendencies towards food. Sonja Yokum, a neuroscientist who studies obesity at the Oregon Research Institute, has been studying exactly that. She showed that food can trigger an addictive-like process in the brain, which tellingly shares the neural symptoms of other more commonly understood addictive disorders, like alcohol and drug addiction. Worryingly, some people are more at risk than others, in part because of how they are wired.

For instance, Yokum revealed that teenagers who had brain areas most attentive towards food were the most risk of gaining an unhealthy amount of weight. “One possible explanation is that some individuals have an elevated reward region responsivity (which could be biologically based), which may render them more vulnerable to food-cue-induced cravings, resulting in greater caloric intake and weight gain,” she explains. This offers one explanation to why conventional weight loss programmes rarely produce lasting effects.

Anna was therefore an ideal trial case for deep brain stimulation, both because of her depression and her addictive-like tendencies towards food, diagnosed by several questionnaires. She represents a subset of obese individuals who fall into the category of an addictive disorder towards food. They typically find it extremely difficult to prevent themselves eating when presented with food, in a similar way that an alcoholic in the midst of addiction may struggle to walk past a bar without going inside.

Further, while these individuals show greater brain activation to food than do individuals of a healthy weight, when they finally get their reward (food), the brain activation decreases. This shows, says Yokum, another factor similar to that found in substance abuse – that addicted people get excitement at the prospect of what they desire, but as soon as they get it, activation in this area actually decreases. This might therefore mean that “they need to eat a lot more to gain the same level of excitement as before”, she says.

This is clearly problematic when it comes to food – a substance we need to survive. Obese individuals who show addictive-like behaviours towards food may find it extremely difficult to control the intake of that which they crave, because it cannot be completely avoided.

That’s why Yokum and her team are developing training tasks that are intended to help obese individuals reset the way their brain responds to food. They do this by showing digital images of health food on a patient and asking them to click ‘like’ towards it, doing the opposite with unhealthy food. “We are trying to train the brain this way,” says Yokum.

Less invasive, not to mention cheaper, techniques like this could be vital in addressing what we know is a worldwide epidemic, with 650 million adults and 340 million children and adolescents currently considered obese. Obesity contributes to an estimated 2.8 million deaths per year worldwide.

While deep brain stimulation is clearly not the answer for the majority, that it shows such positive initial results demonstates that in the most severe cases, experimental treatments can change lives.

There is certainly no one-size-fits-all approach, Anna’s complex case highlights that there is often more than one issue at play contributing to overeating in obese individuals. If we understand that, then a targeted approach like deep brain stimulation can clearly be an important step to help some individuals lose the weight they so desperately want – or even need to.

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Melissa Hogenboom is BBC Future’s staff writer. You can follow her on twitter or facebook.

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