Deep brain stimulation of the subthalamic nucleus normalises Parkinson‘s disease related abnormalities of auditory evoked potentials and quantitative EEG

Objective: Some of the cardinal symptoms of Parkinson’s disease (PD) share a pathological rhythmic dysregulation as common feature, indicating a disturbing rhythmicity within cortical and subcortical networks involving also the basal ganglia (BG). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) clearly improves dopamine-dependent motor deficits in patients with PD. While there is evidence for dopaminergic sensitivity of central sensory processing, the effects of DBS on sensory information processing are less clear.
Methods: We investigated the effects of STN-DBS on auditory information processing, using auditory evoked potentials (AEP) and spectral analysis. We compared power spectra and amplitude, latency and habituation of AEPs in 12 patients with advanced PD to those of age-matched controls. Stimulation consisted in rhythmic metronome-like clicks presented at different inter-stimulus intervals (ISI). High-density EEG-recordings were carried out prior to and 4 months following surgery for STN-DBS in the practically defined OFF-state. We studied the effects of STN-DBS at the individual therapeutic DBS-frequency and with DBS switched off.
Results: Prior to surgery, PD patients showed significantly larger AEP amplitudes (P50, N1 and P2) over central and central-parietal regions compared to controls. Compared to controls N1 and P2 latencies were significantly increased and AEP habituation reduced in PD patients. Moreover, in PD patients the general power level and the power of beta-band oscillations, in particular, were abnormal. Electrode implantation per se as well as STN-DBS had a normalizing effect on AEPs and power spectra. High-frequency STN-DBS led to a normalization of P2, but not P50 and N1 amplitudes. Noteworthy, we could not find any significant difference between the two post-operative conditions Stimulation-ON vs Stimulation-OFF. This could be a hint of the long lasting effects of chronic high-frequency DBS. Due to plastic neuronal changing, switching off the stimulator for 20 minutes is probably not enough to re-stabilize the pre-operative auditory processing state. Another reason could be the changed and reduced post-operative medication.
Conclusions: Our findings support and expand previous reports of dysregulated central auditory processing in PD as expressed by AEPs and power spectra. The present results suggest that STN-DBS differentially affects the auditory evoked responses and may thus also influence sensorimotor processing at higher levels.