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

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 characterize the nonstationarities in spectral parameters, we estimated APFs from 1 s 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.