Spontaneous Fluctuations in Alpha Peak Frequency Along the Posterior-to-Anterior Cortical Plane

Abstract

Alpha peak frequency (APF) is defined as a prominent spectral peak within the 8-12 Hz frequency range. Typically, an individual’s alpha frequency is regarded as a stable neurophysiological marker. A wealth of recent evidence, however, indicates that APF shifts within short timescales in relation to task demands and even spontaneously so. Further, brain stimulation studies often report shifts in APF both within and between experimental sessions, directly contradicting the idea of a stable APF. To characterise the non-stationarities in spectral parameters, we estimated APFs from one-second epochs of resting-state magnetoencephalography (MEG) recordings from healthy adults of either sex. To enhance signal-to-noise ratio, without compromising on temporal resolution, we averaged power spectra within parcelled regions. Our findings indicate that variation in APFs exacerbates along the posterior-to-anterior cortical plane i.e., from the occipital to the frontal cortices. Further, by comparisons with amplitude-matched simulated signals, we demonstrated that the observed gradient is not attributable to measurement noise. Across the cortex, APFs showed poor temporal reliability, raising the question of whether APFs are more like a transient state than a trait. In general, our study elucidates the dynamic characteristics of alpha oscillations and reveals systematic regional differences which are, in part, shaped by underlying signal-to-noise ratio inherent to MEG recordings.

Significance Statement Oscillatory signals, as recorded with electro-/magneto- encephalography, exhibit a prominent peak in the Alpha frequency range (i.e., APF). It is widely accepted that the amplitude and phase of oscillatory signals vary with behaviour. However, the stability of APF within and across experimental sessions is seldom examined. In this study, we characterised the changes in APF to show that the degree of fluctuations in APF systematically increased from the occipital cortex to the frontal cortex, forming a gradient across the cortical surface. We also established that the observed variability was not driven by underlying noise. Our results raise the possibility that the dynamics of APF could be a salient feature of a cortical region, driven by its underlying structure and function.