Wires inserted into the brain delivering jolts of electricity able to alter movement and behaviour may sound like the stuff of a sci-fi movie. But for people suffering from certain neurological conditions, this scenario is real and offers a much-needed source of relief.
Over the past two decades, doctors have turned to deep brain stimulation (DBS) to help people with Parkinson's disease, and movement disorders like essential tremor and primary dystonia, a debilitating condition that causes painful, twisting muscle spasms.
It's already an established treatment for advanced stages of Parkinson's that medication alone can no longer treat. Although it's not a cure, and doesn't halt disease progression, for certain patients it can vastly improve symptoms such as tremors and muscle rigidity that could make the patient dependent on a caregiver.
But the therapy is no longer seen as a last resort. It's also being applied to earlier stages of Parkinson's. Scientists are also exploring other applications for the therapy: to treat obesity, Alzheimer's disease and psychiatric conditions such as depression and obsessive-compulsive disorder.
Chronic stimulation of sub-cortical structures was first used in the early 1950s, but the modern form of DBS, developed in 1987, can be attributed to Alim-Louis Benabid and Pierre Pollak of the University of Grenoble's department of neurosurgery and neurology in France.
The surgery evolved out of the surgeries in which doctors used heat probes to burn and permanently damage small regions of the brain that are known to trigger certain neurological conditions.
In DBS, instead of destroying tissue, a neurosurgeon implants slender millimetre-thick electrodes that pump steady electrical pulses via a battery-powered device - a "brain pacemaker" - that's implanted in the chest.
The device is programmed externally with a remote, hand-held controller to fine-tune the electrical stimulation for individual patients.
The US Food and Drug Administration approved the surgery for "essential tremor" in 1997 and for tremors associated with Parkinson's disease in 2002.
DBS was first introduced in Hong Kong in 2007 at the Prince of Wales Hospital. The first patient benefited from the treatment for more than 16 years and had to undergo battery changes only twice at six-year intervals, according to Professor Poon Wai-sang, chief of neurosurgery at Chinese University.
Benefits vary among patients according to the severity of their condition. "Our initial selection of patients was conservative - choosing the most disabled patients. [But] it turned out that the moderately disabled patients benefited most," Poon says.
A recent two-year clinical trial found it might improve overall quality of life and social functioning in patients in earlier stages of Parkinson's, too. In the past, doctors have relied solely on drugs in this period.
The study, published in February in the New England Journal of Medicine, showed that DBS was more effective than other medical treatment in patients with Parkinson's disease and early motor complications. The study's lead investigator, Dr Günther Deuschl, a professor of neurology at Christian-Albrechts-University in Kiel, Germany, says: "These results signal a shift in the way patients with Parkinson's disease can be treated."
In Singapore, about one or two cases of DBS are performed each month at the National Neuroscience Institute, according to Professor Ng Wai-hoe, head of the institute's neurosurgery department. "At present, we normally offer DBS to [Parkinson's] patients with moderate disease severity; that is, when patients begin to experience problems with their motor system or when they develop adverse effects from medication," Ng says.
"The surgery takes two to three hours but can vary depending on the technique used by the functional neurosurgeon. At the National Neuroscience Institute, we make use of both anatomical targeting and microelectrode recording to place the electrode."
A new, safer way to perform the surgery, detailed in an article last month in the Journal of Neurosurgery, could expand significantly the number of patients who might be candidates for DBS surgery. Using advances in brain imaging, the new technique - tested in 60 patients - allows for extremely accurate electrode placement. Implanting them is painstaking: it starts with boring a hole through the skull and threading the electrodes deep into the brain, aiming for a spot that's a fraction of the size of a pea.
"Patients don't need to be awake during this surgery - which will mean many more patients who can be helped by this surgery will now be willing to consider it," says Dr Kim Burchiel, chair of neurological surgery at Oregon Health & Science University and lead author of the study.
Apart from Parkinson's, DBS is now also being tested for Alzheimer's, another form of dementia that also has no cure and is not easily managed.
Dr Douglas Scharre, from the Ohio State Wexner Medical Centre in the US, says the disease is progressively disabling, with loss of memory, cognition and worsening behavioural function.
His team enrols patients with mild or early-stage Alzheimer's to determine whether DBS treatment can improve brain function involved in cognition and behaviour.
DBS could also help people with conditions such as intractable depression, refractory epilepsy, obsessive compulsive disorders and drug addiction.
Addiction can take many forms, including binge eating and alcohol dependence - both of which are being targeted with DBS therapy. In mice and people who overeat compulsively, scientists have pinpointed an abnormality in the regulation of the brain's reward system. Through tests on obesity-prone mice, researchers at the University of Pennsylvania in the US reported in April that DBS reduces binge eating.
"Once replicated in human clinical trials, DBS could rapidly become a treatment for people with obesity due to the extensive groundwork already established in other disease areas," says study lead author Dr Casey Halpern.
For alcoholism, lab tests on rats have shown that DBS consistently reduced alcohol consumption in the rodents. Tests on human alcoholics show that DBS treatment produced less risky and more controlled behaviour accompanied by reduced drinking.
Intriguingly, while the effects of DBS are reportedly reversible, doctors have been surprised to find patients who continued to enjoy symptom relief even after their devices were switched off.
A recent study reported that two patients being treated for dystonia had their DBS devices accidentally switched off for months, but they only noticed it when mild symptoms returned.
Dr Michele Tagliati, director of the movement disorders programme at Cedars-Sinai Department of Neurology in the US, says: "Current thought is that symptoms will worsen within hours or days of device shut-off, but these two young men continued to have clinical benefit despite interruption of DBS therapy for several months.
"To our knowledge, these two cases represent the longest duration of retained benefit in primary generalised dystonia."
Moreover, when these patients' symptoms did return, the severity was far milder than it was before DBS, Tagliati says.