The acute effects of dopaminergic medication and deep brain stimulation of subthalamic nucleus on basic executive functions including shifting, updating and inhibition in Parkinson’s disease patients

Abstract

The general aim of the present PhD thesis is to investigate the effects of two common treatments of Parkinson’s disease (PD), dopamine medication and deep brain stimulation (DBS) of the subthalamic nucleus (STN), on executive functions (EFs) including the abilities of shifting, updating and inhibition in patients relative to age-matched healthy controls. The thesis consisted of four studies. Study 1 examined the acute effect of dopamine medication on PD patients who had been previously diagnosed with impulsive control disorders (ICDs) using a moving dots paradigm to assess their abilities of context monitoring. Study 2 created predictive models using behavioural data from the previous studies to build classification predictive models, to demonstrate that behavioural patterns on a moving dots task could potentially be used as a screening tool in predicting vulnerability to develop ICDs in PD patients. Study 3 examined the acute effects of STN DBS on task switching using a moving dots paradigm in PD patients. Study 4 investigated the acute effects of STN DBS on reprogramming actions when encountering surprising events, using a probabilistic reaction time (RT) task. It was hypothesised that for both treatments, being ON states would induce impaired executive functions that lead to faster RTs and more incorrect responses in PD patients, due to the ‘dopamine overdose hypothesis’ and the DBS interrupting the role of the STN in inhibitory control. In summary, the acute manipulation of both treatments did not render significantly negative effects on PD patients behaviourally. However, PD patients still showed certain difference on task performance compared to age-matched healthy controls, which may shed lights on the role of basal ganglia in basic abilities of EFs. Furthermore, the behavioural patterns on tasks involving core aspects of EFs may potentially be used to predict the onset of ICDs, which provides benefits to clinical purpose