OscillTrack: Real-time oscillatory phase and amplitude tracking for closed-loop stimulation

Various oscillations are associated with specific aspects of brain function. Oscillations arise from coordinated neuronal activity in reciprocally connected and looping brain networks. Closed-loop brain stimulation precisely aligned to the structure of ongoing activity can be a powerful tool for understanding brain function and providing interventions to ameliorate pathological activity. OscillTrack is a computationally lightweight approach to track primarily the phase and also the amplitude of a waxing and waning oscillation within a frequency band of interest. OscillTrack directly operates on the wide band signal removing the need for a separate pass-band filter and associated filter delays. It performs a continuous transformation on the data stream, instantaneously providing phase and amplitude estimates for each sample as soon as that sample is available. It does not operate on chunks or windows of data. Instead, it performs a computationally inexpensive calculation on receipt of each sample and only retains three state variables between samples for use in the next iteration. We used OscillTrack to deliver electrical stimulation aligned to eight different phases of beta oscillations in 6-OHDA lesioned rats. In these experiments we were successful in producing different states of brain-machine equilibrium resulting in amplification or suppression of the oscillation depending on the phase targeted. We have implemented it in C code for use in an embedded processor and in Verilog for use in an FPGA and we make it available for academic research use (https://colinmcn.github.io/OscillTrack/).Figure: Stimulation triggered averages from ECoG traces when OscillTrack targeted electrical stimulation to eight different phases.