A detailed and very interesting study published this week in the journal Brain is the work of several German and Canadian doctors who focused on personal and social implications of people with PARKINSON’S DISEASE who had undergone deep brain stimulation (DBS) of the sub-thalamic nucleus (STN). While the DBS offers marked improvements in motor function that definitely improves the quality of life from a movement perspective, many of these people report serious struggles with social and work related problems. Aspects of a behavioral and social nature are rarely studied in relation to DBS treatment.
The researchers noted that while DBS of sub-thalamic nucleus (STN) is beneficial for motor symptoms, the region stimulated also affects areas of decision making and impulsivity. This may have the effect of making these people feel over confident and encourages risk-seeking behaviors. Parkinson Disease sufferers may or may not be aware of this shift in their impulsivity but it may be the basis for some of their personal and work related issues. The researchers hypothesized that DBS-STN causes a pathological change in the way self estimation is perceived in competitive situations.
In order to analyze the self awareness of Parkinson’s disease patients who had had DBS of STN, they used an experiment from behavioral economics that consisted of addition of a long string of numbers. Groups tested consisted of people with PARKINSON’S DISEASE who had received DBS of Sub-Thalamic Nucleus, people with PARKINSON’S DISEASE who had not received DBS of Sub-Thalamic Nucleus, and non-Parkinsonian controls. There were four sets of numbers with varying rewards, paired as low risk/low reward, low risk/high reward, to high risk/high reward.. Further, as the subjects progressed from one set to the next, they were asked to estimate their accuracy, and then to choose whether to accept a nominal “prize” or to continue on to a “tournament”. In all the sets, the controls had the highest accuracy and the DBS-STN the lowest. As they progressed, the DBS-STN had higher predictions of their accuracy, even though past performance was negative. 26% of the DBS-STN consistently chose high risk/high reward even though based on past performance this was not to their benefit.
This study generated data on many areas of performance and behavior. One area examined the risk taking behavior of the DBS of Sub-Thalamic Nucleus group compared to the non DBS group. While very similar in symptoms and length of disease, the non DBS group was less inclined to risk taking behavior leading the researchers to surmise that perhaps there was an inherent bias toward risk taking behavior in the DBS-STN group that perhaps lead them to undergo the potentially risky, invasive DBS surgery in the first place.
In conclusion, the study authors suggest that while the DBS of Sub-Thalamic Nucleus subjects are impaired in their self-estimation, they may naturally have a preference for competitive situations, but that the DBS-STN has impaired the pathways used to evaluate both their decision making skills and the risks involved. This may help explain some of the social difficulties this population experiences in their work, social and personal lives.
E. Florin, D. Muller, J. Pfeifer, M. T. Barbe, G. R. Fink, L. Timmermann; Subthalamic stimulation modulates seslf–estimation of patients with Parkinson’s disease and induced risk-seeking behavior; Brain (2013) doi: 10.1093/brain/awt241 pub 9/25/2013