Abstract

The properties of time-domain electroencephalographic data have been studied extensively. There has however been no attempt to characterize the temporal evolution of resulting spectral components when successive segments of electroencephalographic data are decomposed. We analysed resting-state scalp electroencephalographic data from 23 subjects, acquired at 256 Hz, and transformed using 64-point Fast Fourier Transform with a Hamming window. KPSS and Nason tests were administered to study the trend- and wide sense stationarity respectively of the spectral components. Their complexities were estimated using fuzzy entropy. Thereafter, the rosenstein algorithm for dynamic evolution was applied to determine the largest Lyapunov exponents of each component’s temporal evolution. We found that the evolutions were wide sense stationary for time scales up to 8 s, and had significant interactions, especially between spectral series in the frequency ranges 0-4 Hz, 12-24 Hz, and 32-128 Hz. The highest complexity was in the 12-24 Hz band, and increased monotonically with scale for all band sizes. However, the complexity in higher frequency bands changed more rapidly. The spectral series were generally non-chaotic, with average largest Lyapunov exponent of 0. The results show that significant information is contained in all frequency bands, and that the interactions between bands are complicated and time-varying.

Highlights

  • A typical EEG data acquisition pipeline can be modelled as a time-domain operation, with data acquired from multiple electrodes at a fixed sampling rate leading to a time series, x[t] = xt1, xt2, ⋯, xtN from each electrode

  • Time domain methods thereafter proceed by manipulating x[t] directly, but for frequency domain methods, further processing is preceded by spectral decomposition of x[t], or of multiple sub-sequences of it, taken one at a time

  • The goal of this study was to characterize the temporal evolution of these spectral component time series, leading to an understanding which would, among other things, allow correct assumptions to be made during further processing of frequency-domain data

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Summary

Introduction

Time domain methods thereafter proceed by manipulating x[t] directly, but for frequency domain methods, further processing is preceded by spectral decomposition of x[t], or of multiple sub-sequences of it, taken one at a time. F: t → ω to a sub-sequence xj[t] = xtj, xtj2, ⋯ , xtjn of x[t], generates a spectral series Xj[ω] = Xωj 1, Xωj 2, ⋯ , Xωj m, where j ∈ {1,2,3. If J sub-sequences of uniform length n can be extracted from x[t], and the subsequences are constrained to be contiguous and mutually exclusive, J = ⌊N/n⌋, where ⌊⋅⌋ is the floor function, and the transform F[⋅] can be applied to each subsequence, yielding the matrix: Xω1 1 Xω1 2 Xω1 3.

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