Objective: To investigate whether motor cortical oscillation changes in fractal patterns are associated with a change in the FD in the HALO and the 6-OHDA rat model of PD.

Background: Previous studies demonstrated enhanced beta-band activity in rat models (haloperidol (HALO), and 6-hydroxydopamin (6-OHDA)) of Parkinson disease (PD), which was reduced after administration of the dopamine-receptor agonist apomorphine (APO) or deep brain stimulation (DBS) of the subthalamic nucleus (STN), respectively. Fractal dimension (FD) analysis is a nonlinear approach that quantifies the complexity of neuronal activity. Little is known about nonlinear analytic approaches, such as FD analysis, to characterize pathological network activity in PD.

Method: In the acute HALO rat model of PD, an ECoG array was placed subdurally above the MCtx area in male Sprague-Dawley rats. Thereafter, ECoG was recorded in the free moving rat in three conditions: (1) basal activity, (2) after injection of HALO (0.5 mg/kg), and (3) with additional injection of APO (1mg/kg). In the chronic model, 6-OHDA was unilaterally injected into the medial forebrain bundle, sham-lesioned control rats received vehicle. A stimulation electrode was then implanted in the ipsilateral STN, and an ECoG array placed subdurally above the MCtx area. Thereafter, ECoG was recorded in the free moving rat with two conditions: (1) during basal activity, and (2) during STN DBS. The ECoG signals were band-pass filtered between 1–100 Hz and sampled at 1 kHz. Furthermore, the raw data were down-sampled at 250 Hz and Higuchi’s FD algorithm was applied for analysis of the raw ECoG data.

Results: In the MCtx area, the average FD values were higher in both the HALO and the 6-OHDA rat model as compared to basal activity and sham-lesioned control rats. Further, injection of APO or STN DBS decreased the average FD values in both models (P<0.001).

Conclusion: In PD rat models, the neural dynamics can also be characterized by FD. The non-linear analysis of FD allows to detect oscillation-based pattern changes achieving robust temporal resolution. This analytic approach may be integrated into future research concerning therapeutic algorithms for PD, such as adaptive closed loop stimulation, thus providing an alternative and possibly efficient biomarker of pathological network activity in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/complexity-of-fractal-patterns-in-motor-cortical-oscillatory-activity-in-rodent-models-of-parkinson-disease/