Is Deep Brain Stimulation a Cure-all?

Is there anything that can't be fixed by burrowing an electrode array into the deep tissues of the brain? With varying degrees of success, deep brain stimulators have been used to temporarily defog clouds of chronic depressionstamp out migraines before they cycle out of control, and steady the movement of people with Parkinson's disease. Well, now you can add Tourette syndrome to this list of maladies.

A study in the current issue of Neurology follows 18 patients with severe Tourette syndrome for two years after having neurosurgery. During the procedure, an array of electrodes is inserted into the patient's thalamus. Wires running from the device connect to a pulse generator implanted just beneath the skin on the chest. All the parts are internal and, when activated, stimulate a highly targeted area of the brain.

Those who continued with the treatment (3 either dropped out or were removed by the researchers) showed a significant decrease in the motor and verbal tics associated with the disorder. In all but one patient, obsessive behaviors and symptoms of depression improved, both of which are commonly present in patients with severe Tourette syndrome.

The authors are refraining from drawing any conclusions until more controlled experiments have been conducted and they acknowledge the risks inherent in an invasive therapy like DBS.

But even the preliminary results beg the question: how can one treatment option yeild a good outcome for so many different disorders? And, overwhelmingly, the answer is, "we don't know." What we do know is which parts of the brain are best targeted for different disorders, suggesting that we know much more about the "where" than the "why" with DBS.

Andrea Cavanna, a lead author on the study, explains that "little is known about the patho-physiology of Tourette syndrome. However, dysfunction in the fronto-basal pathways seems to play a relevant role in tic generation and associated behavioral problems. The targeted thalamic nuclei are the final common outputs of the involved pathways."

So, they try it, and it seems to work. But I can't help thinking that researchers will be able to perfect therapies like deep brain stimulators only once we have fully explained the disorders they seek to treat. And that this, rather than the technology, is what holds us back.

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