Parkinson subtype-specific Granger-causal coupling and coherence frequency in the subthalamic area

- Combination of coherence and Granger causality.
- Analysis of interaction between local field potentials and muscle activity.
- Detect Parkinson subtype-specific coupling frequency and causality pattern.
- Different pathways pathologically altered in the Parkinson subtypes.

Previous work on Parkinson's disease (PD) has indicated a predominantly afferent coupling between affected arm muscle activity and electrophysiological activity within the subthalamic nucleus (STN). So far, no information is available indicating which frequency components drive the afferent information flow in PD patients. Non-directional coupling e.g. by measuring coherence is primarily established in the beta band as well as at tremor frequency. Based on previous evidence it is likely that different subtypes of the disease are associated with different connectivity patterns. Therefore, we determined coherence and causality between local field potentials (LFPs) in the STN and surface electromyograms (EMGs) from the contralateral arm in 18 akinetic-rigid (AR) PD patients and 8 tremor-dominant (TD) PD patients. During the intraoperative recording, patients were asked to lift their forearm contralateral to the recording side. Significantly more afferent connections were detected for the TD patients for tremor-periods and non-tremor-periods combined as well as for only tremor periods. Within the STN 74% and 63% of the afferent connections are associated with coherence from 4-8 Hz and 8-12 Hz, respectively. However, when considering only tremor-periods significantly more afferent than efferent connections were associated with coherence from 12 to 20 Hz across all recording heights. No difference between efferent and afferent connections is seen in the frequency range from 4 to 12 Hz for all recording heights. For the AR patients, no significant difference in afferent and efferent connections within the STN was found for the different frequency bands. Still, for the AR patients dorsal of the STN significantly more afferent than efferent connections were associated with coherence in the frequency range from 12 to 16 Hz. These results provide further evidence for the differential pathological oscillations and pathways present in AR and TD Parkinson patients.