过犹不及：脑部深刺激装置让帕金森患者易激冲动

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Implantable Brain Device Makes Parkinson's Patients More Impulsive

There is an implantable brain device which is used with Parkinson's Disease patients to help them control their movements better. However, there have been reports that some of those who have had the device implanted are becoming more impulsive.

When the Deep Brain Stimulation (DBS) device was first used the benefits were so impressive that not much focus was spent investigating what side effects there might be. Experts stress that despite this undesirable side effect, they still believe the benefits outweigh the negatives. Rather, there should be more focus on making adjustments to benefit the patient's quality of life.

It is being reported that a number of Parkinson's Disease patients who have this device may not think rationally at times, and do things or make decisions they might later regret. A study found that when the brain stimulation was switched off the patients started behaving normally again, especially when under stress.

Our brains are designed to take a step back and think things through when we are faced with difficult choices. This brain implant, that stops the tremors experienced by Parkinson's patients, seems to take away this inhibition and make people much more impulsive. Parkinson's medications have been known to trigger compulsions, such as pathological gambling.

In the case of this brain implant, an article in the journal Science found that some patients who had this device did not seem to learn from bad experiences. The researchers from the University of Arizona said the implant does not block learning, it just prevents the patient from hesitating when faced with a difficult decision - he/she becomes impulsive.

One of the patients the researchers were studying completely forgot he was wheelchair bound when he saw something on the other side of the room and tried to run to it - they managed to catch him just as he fell to the ground.

There is a part of the brain called the subthalamic nucleus. Scientists say it is responsible for controlling movement, but also for controlling impulsive behavior. The deep brain stimulation device consists of electrodes which are placed in this region of the brain. The researchers believe that when they are switched on they not only control excessive body movements, but also block our ability stop and weigh our options (hesitate, take time to decide).

Perhaps Parkinson's patients who have the device implanted should be given counseling after their operation, say the researchers.

This study consisted of 46 participants. 15 were Parkinson's patients who were taking dopamine drugs, 17 had received the DBS implant, while the other 14 were healthy elderly adults (did not have Parkinson's). They had to tackle specialized computer games which tested their decision making behavior.

In their first test, the participants looked at pairs of Japanese written characters and asked to select the 'correct' one in each pair. The participants gauged their progress by observing the computer's response to each of their decisions - the computer would respond with either 'correct' or 'incorrect'. The aim here is that the more you play and watch the computer response, the better your get at spotting the correct characters.

After a while the symbols were paired differently so that there could be pairs which were both correct, pairs which were both incorrect, and mixed pairs. When faced with correct-correct or incorrect-incorrect pairs the patients on dopamine and the healthy participants hesitated (they had to pick one), while the DBS patients did not hesitate at all. As soon as the implants were switched off the DBS patients started to hesitate like the others - this not only demonstrated that the implants were encouraging impulsive behavior, it also showed that the implants did not block learning (otherwise the patients would not have hesitated as they would not have learnt anything during the first round anyway).