Relation of Neural Beta-Oscillations of the Subthalamic Nucleus to Clinical Symptoms of Parkinson’s Disease

Abstract

Beta oscillations within the subthalamic nucleus (STN) are proposed to serve as biomarker for Parkinson’s disease. A wealth of data indicate essential functional differences between two subbands – low beta (13–19 Hz) and high beta (20–30 Hz), but there is still no full understanding of their specialization. We collected postoperative LFP data using externalized leads from 6 PD patients with implanted bilateral STN DBS electrodes before and after levodopa administration. We studied the relationship between parameters of low and high beta activity and motor symptom scales (UPDRS3, bradykinesia and rigidity). Mean PSD in both subbands decreased after levodopa administration. Low beta mean PSD was positively correlated with all three inspected motor scales (UPDRS3, rigidity and bradykinesia), while high beta mean PSD correlated only with rigidity. Most of the oscillatory peaks were concentrated within the high beta band. Their number decreased after levodopa administration, still leaving a prominent part unaffected. Almost all the low beta peaks compiling small initial number have disappeared after levodopa administration, thus we analyzed only high beta peak parameters. High beta peak frequency and amplitude changed with OFF-ON transition and were correlated with only rigidity scores. Our findings indicate that, although both low and high beta respond to medication state, there are functional differences between the subbands: low beta reflects motor symptoms non-specifically, while high beta is more specialized and reflects rigidity.