Limitations of the study and future directions
An important limitation of this study is the relatively small sample size. Nevertheless, an appropriate statistical analysis applied by us (for inter-group comparisons and for correlations calculations) was able to reveal an effect of dopaminergic system pathophysiology in PD PET/CT neuroimaging, PSD-EEG and neuropsychological parameters outcomes even in this relatively small sample size. However, due to this relatively small sample size, the results of this study cannot be generalized for the whole PD patients population. Another important limitation of our study is the choice of only two neuropsychological cognitive tests (TMT and ST). This choice narrowed down a range of our considerations on associations of the PD-specific EEG brain waves slowing and dopaminergic deficiency with disordered executive functions in tested by us PD patients. Hence, further studies are needed using multimodal scientific approach, with an application of electroencephalography (using EEG recordings with resting and cognitive paradigms), PET/CT neuroimaging methods (using dopaminergic and other PD-specific radiotracers) and broad PD-specific battery of cognitive tests.