A novel method for calculating beta band burst durations in Parkinson's disease using a physiological baseline

Abstract

Background: Pathologically prolonged bursts of neural activity in the 8-30 Hz frequency range in Parkinson's disease have been measured using high power event detector thresholds.

New method: This study introduces a novel method for determining beta bursts using a power baseline based on spectral activity that overlapped a simulated 1/f spectrum. We used resting state local field potentials from people with Parkinson's disease and a simulated 1/f signal to measure beta burst durations, to demonstrate how tuning parameters (i.e., bandwidth and center frequency) affect burst durations, to compare burst duration distributions with high power threshold methods, and to study the effect of increasing neurostimulation intensities on burst duration.

Results: The baseline method captured a broad distribution of resting state beta band burst durations. Mean beta band burst durations were significantly shorter on compared to off neurostimulation (p = 0.0046), and their distribution shifted towards that of the 1/f spectrum during increasing intensities of stimulation.

Comparison with existing methods: High power event detection methods, measure duration of higher power bursts and omit portions of the neural signal. The baseline method captured the broadest distribution of burst durations and was more sensitive than high power detection methods in demonstrating the effect of neurostimulation on beta burst duration.

Conclusions: The baseline method captured a broad range of fluctuations in beta band neural activity and demonstrated that subthalamic neurostimulation shortened burst durations in a dose (intensity) dependent manner, suggesting that beta burst duration is a useful control variable for closed loop algorithms.

Keywords: Beta fluctuations; Burst durations; Deep brain stimulation; Local field potentials; Parkinson’s disease; Thresholding.

Figure 1:

Local field potentials from a Parkinsonian patient are compared to simulated 1/f pink noise matched to the same roll off. Broad spectrum Parkinsonian local field potentials (A) are larger in amplitude than the simulated pink noise (B). Both signals are plotted on the same PSD (C), the power in the beta (13–30Hz) frequency range is elevated when compared with the gamma frequency range (40–70Hz). (D) Sub bands of the Parkinson’s and pink noise gamma (blue lines) and beta (green lines) from C are band pass filtered showing the elevation of power in the beta frequency range (Bottom Right).

Figure 2:

Bandpass filtered PD LFP and pink noise filtered for the gamma frequency band (CF = 54 Hz, BW = 6Hz). Parkinson’s gamma band data (A) and simulated pink noise data (B) are shown using the same axes. LFP power (black), identified troughs (red dots), thresholds (red line) and identified bursts using the Anderson method in PD (C) and pink noise (D). Histograms of the associated burst durations for PD (E) and pink noise (F) are similar.

Figure 3:

Burst durations are calculated for the baseline method using 1000 runs of simulated pink noise. The effects of bandwidth and center frequency (10, 15, and 20 Hz) are shown. Error bars represent standard deviations of the mean.

Figure 4:

Comparison of the three burst duration methods (Baseline, High Power Detection Lower Threshold, High Power Detection/Threshold) processed with the same center frequency (18.1Hz) and bandwidth (6 Hz). (A) Bandpass filtered LFP used for each analysis. Squared LFP and power envelope for the Baseline (B, E), High Power Detection Lower Threshold (C, F), and High Power Detection/Threshold (D, G) methods. Histograms of the resulting burst durations for the Baseline (H), High Power Detection Lower Threshold (I) and High Power Detection/Threshold (J) methods. Red line indicates the threshold for burst quantification (E, F, G) and the blue line represents the threshold for burst selection (F).

Figure 5:

Beta power and burst durations are suppressed by deep brain stimulation. (A) Five different stimulation conditions (0%, 25%, 50%, 75% and 100% of clinical equivalent stimulation) are compared with simulated 1/f pink noise in a representative individual. Vertical red bars, a subset of the beta frequency band used for analysis in B that is highly dependent on stimulation intensity. (B) Burst durations calculated for the same 30 second windows are decreased with increasing levels of stimulation and are driven towards the normal burst duration expected with simulated pink noise as calculated by the baseline method. Mean burst durations are shown by labeled red bars. Boxplots of mean burst durations demonstrating the effect of deep brain stimulation on mean beta burst durations as calculated by the: C, baseline; D, high power detection/lower threshold; E, high power detection/threshold at 0%, 25%, 50%, 75%, and 100% Vmax. The thick black line represents the median and the open circle represents the group mean.