Aperiodic phase re‐setting in scalp EEG of beta–gamma oscillations by state transitions at alpha–theta rates

Abstract

Abstract:We evaluated the rapid changes in regional scalp EEG synchronization in normal subjects with spatial and temporal resolution exceeding prior art 10-fold with a high spatial density array and the Hilbert transform. A curvilinear array of 64 electrodes 3 mm apart extending 18.9 cm across the scalp was used to record EEG at 200/sec. Analytic amplitude (AA) and phase (AP) were calculated at each time step for the 64 traces in the analog pass band of 0.5-120 Hz. AP differences approximated the AP derivative (instantaneous frequency). The AP from unfiltered EEG revealed no reproducible patterns. Filtering was necessary in the ␤ and gamma ranges according to a technique that optimized the correlation of the AP differences with the activity band pass filtered in the alpha range. The sizes of temporal AP differences were usually within Ϯ0.5 radian from the average step corresponding to the center frequency of the pass band. Large AP differences were often synchronized over distances of 6 to 19 cm. An optimal pass band to detect and measure these recurring jumps in AP in the ␤ and ␥ ranges was found by maximizing the ␣ peak in the cospectrum of the correlation between unfiltered EEG and the band pass AP differences. Synchronized AP jumps recurred in clusters (CAP) at ␣ and theta rates in resting subjects and with EMG. Cortex functions by serial changes in state. The Hilbert transform of EEG from high-density arrays can visualize these state transitions with high temporal and spatial resolution and should be useful in relating EEG to cognition.

Origin, structure, and role of background EEG activity. Part 4: Neural frame simulation

“…Amplitudes were calculated in four ways. The simplest was the root mean square (rms) of the filtered real part at each location and across each stabilized frame [Freeman and Burke, 2003]. Virtually the same results obtained from the gain coefficient of the FFT of the filtered EEG in the frame at the peak frequency.…”

“…The EEG patterns in the frames were spatial amplitude modulations (AM) of a spatially coherent, aperiodic oscillatory waveform, which was defined as a carrier wave. The power spectral densities (PSD) of the EEGs had power-law distributions (1/f) in log-log displays; the maximal energy of carrier waves was in spectral peaks in the beta (12-30 Hz) or gamma ranges, while the repetition of frames gave peaks in the theta and alpha ranges [Freeman, Burke and Holmes, 2003]. The onset of each frame was by a state transition in which the phase of the carrier wave was re-initialized and then re-synchronized within a few ms, whereupon its AM pattern emerged, stabilized, increased in intensity to a brief maximum, and then decayed after 3 to 5 cycles of the carrier wave with phase and frequency dispersion [Freeman, 2004a,b].…”

Cerebral Energy Metabolism and the Brain’s Functional Network Architecture: An Integrative Review

“…The dynamic coherence of oscillatory activity in different frequency bands underlies the synchronization of distributed neural responses in both local and extended networks. [1][2][3] Experimentally, synchronous activity fluctuations across the brain are often translated into graphical representations for visualization and analytical purposes. In such network depictions of brain activity, anatomically distinct brain areas that constitute the network nodes are 'functionally connected' to each other if their activity time series correlate above a predefined statistical threshold.…”

Reflections on a giant of brain science

“…Development of the cinematic theory of cognition (Freeman 2006b). According to Freeman, the cortical code consists of repetitive spatial frames of metastable amplitude modulation (AM) patterns (Freeman 2000a(Freeman , b, 2003(Freeman , 2004a(Freeman , b, 2005(Freeman , 2006bFreeman et al , 2003aFreeman and Rogers 2002). In this model, the AM patterns are the movie frames, while the rapid transition from one AM pattern to the other acts as the shutter (Freeman and Quian-Quiroga 2013;Davis et al 2013;Kozma and Freeman 2014).…”