Non-linear input-output relationships in the subthalamic nucleus of Parkinson's patients

Both local field potentials (LFP) and spiking (SPK) activity in the subthalamic nucleus (STN) are related to Parkinsons disease (PD) symptoms; however, their relationship is poorly understood. We explore it by separating STN signals of 146 PD patients (308 trajectories, >25,000 recording sites) into aperiodic and periodic components and whitening these signals using their corresponding aperiodic parameters. The LFP aperiodic exponents resemble Brown noise ( = 2.20 {+/-} 0.40) and are significantly higher than SPK aperiodic exponents ( = 0.11 {+/-} 0.22, White noise). The periodic oscillations of LFP are overwhelmingly distributed in the high beta frequency domain while those of SPK are in both low and high beta domains. Beta oscillation center frequencies were downshifted in SPK relative to simultaneously recorded LFP. This demonstrates that the STN synaptic input (LFP) undergoes significant modifications when transformed into STN output (SPK) of PD patients, and may explain the critical role of STN in PD physiology and STN-Deep-Brain-Stimulation therapeutic efficacy.