Deep brain stimulation: Mr. Hyde at your fingertips

20. July 2012

If no medication works, deep brain stimulation is an option for treating patients with neurological diseases. Disadvantage: The electrical impulses can cause extreme changes in personality.

“It is already the biggest advance after the discovery of L-dopa.” This is how Lars Timmermann from the University of Cologne sees the success of this therapy for Parkinson’s disease patients. Do electrical impulses in the brain help as much as those of a pacemaker?

Improvement within minutes

Often the tremor is gone within a few minutes. The movement disorders get better almost instantly after the doctor has pressed the power button. Not only with Parkinson’s disease, but also with depression it appears that the success story of Deep Brain Stimulation continues. Thomas Schlaepfer from the Bonn University Clinic has reported that seven out of ten patients treated there felt much better after intervention.

Still, neurosurgeons mainly undertake these efforts with patients when medications can not do anything more. It is however too early to have total faith that everything will be OK once the current flows through the electrodes. For, in addition to the risks of surgery, not all stimulation effects lead to a truly better quality of life. Especially with Parkinson’s patients, approximately one in two has a change of character, of his or her personality. Christiane Woopen is engaged in a German-Canadian research project on the psychosocial consequences of the brain pacemaker. Often patients have become more confident and motivated, sometimes, as she explains, however also depressed or even aggressive. Family and friends mention for about half of all those patients operated a change in character.

Behaviour change at the push of a button

With some 65, 000 implantations worldwide in the last 15 years, 60 studies have described the adverse side effects. Delusional disorder, hallucinations, apathy, hypersexuality or manic states are such examples.

There’s one 64-year-old with no previous psychic illness who, after the Deep Brain Stimulation used against his Parkinson’s symptoms, became prone to kleptomania. His aggressiveness sometimes manifests itself even in scuffles and fistfights. One architect instead of drawing buildings suddenly started producing female nudes. Another one developed a tendency after the stimulation therapy toward excessive self-esteem, plans reckless financial business deals and spends a great deal of time writing religious poems, although he had previously never been interested in spiritual matters. Another patient via the stimulation even developed pedophilia. Interestingly: with some the manic states can really be turned on and off with the switch attached to the electrodes. In the off mode, the patient had to struggle with his or her typical symptoms, but regretted his or her actions during the manic episode.

Relationship problems due to sudden independence

However due to the seamlessly regained independence alone, many families are overwhelmed. “Some family members enjoy that and the partnership develops again in a new way very creatively”, says Woopen describing their experiences, “others do not handle it, the patients don’t either and the partnership face problems”. Thus the improved status of Parkinson’s patients leads in the worst case to separation. These here are not isolated cases: in every second case the brain pacemaker changes the partner relationship, very often for the worse.
Because Parkinson’s disease however without surgical intervention also leads to personality changes, there is still no accurate set of figures addressing the extent of the change of character that comes via the electrode. The target point for the pulses in this disease is usually in the subthalamic nucleus, a region the size of a pea. The high-frequency pulses interfere with the signals of the nerve cells which fire in unison and thus trigger the symptoms. From there, many paths run to the limbic system, therefore having influence on character and behaviour. It is not always the case however that the surgeon strikes this small region precisely.

Check your risk before surgery

“In severe cases we have to turn off the stimulator again“, says Lars Timmermann. The dangerous procedure has then been done to the brain practically in vain. To reduce the risk of such failures, the NRW clinics of Cologne, Aachen and Dusseldorf have devised a screening test with which the doctors already before the surgery should be able to recognise tendencies to mental disorders. Are there indicators for depression, deficits in cognitive flexibility?
Besides “non-surgery”, there are other alternatives. While true that stimulation of the globus pallidus internus does not quite produce such dramatic effects on motion control, it also however for that reason does not affect the mind. A further possibility is offered by the nucleus ventralis intermedius of the thalamus. Also, the spinal cord could one day become the target of electrical impulses, because natural disruption in Parkinson’s patients comes not only from the brain, but also in the opposite direction out of the muscles. A counter-stimulation then breaks this feedback loop.

Mental health care for all the electrode carriers

In other diseases such as depression, Obsessive-Compulsive Disorder, and even in patients in a coma, a change in character is not undesirable. With depression, the electrodes preferably stimulate nerve cells in the nucleus accumbens or the front capsula interna. Unexpected reactions are rarely described here, desirable changes do not develop immediately, but over months and years. Nevertheless, with mentally disturbed patients specific ethical issues also arise: should one operate on a person also in an instance of limited ability in making decisions? Can a guardian agree to an operation that changes the personality?

For Parkinson’s disease patients, neurologists and medical ethicists agree broadly as such: the patient should know before any surgery to which he or she commits – to improvement of his disease state, but perhaps also to a potential transformation of his or her personality. This also applies to the partner who lives with him or her. The University Hospital of Cologne already implements these steps as requirements. As part of the German-Canadian research project ELSA-DBS (Ethical, Legal and Social Aspects of Deep Brain Stimulation), psychologists support the surgical candidates both before and after surgery. “Maybe we would have gotten divorced without this support” is something that has been heard as part of the praise patients and family have made of this option path. It is expensive. In instances of adverse psychological changes, turning off the device again and leaving the patient alone with his suffering is perhaps even more expensive.

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Medicine, Neurology

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