Inter-individual differences in occipital alpha oscillations correlate with white matter tissue properties of the optic radiation

Abstract

Neural oscillations at approximately 10 Hz, called alpha oscillations, are one of the most prominent components of neural oscillations in the human brain. In recent years, characteristics (power/frequency/phase) of occipital alpha oscillations have been correlated with various perceptual phenomena. However, the relationship between inter-individual differences in alpha oscillatory characteristics and the properties of the underlying brain structures, such as white matter pathways, is unclear. A possibility is that intrinsic occipital alpha oscillations are mediated by thalamocortical interaction; we hypothesized that the most promising candidate for characterizing the intrinsic alpha oscillation is optic radiation (OR), which is the geniculo-cortical pathway carrying signals between the lateral geniculate nucleus (LGN) and primary visual cortex (V1). We used resting-state magnetoencephalography (MEG) and diffusion-weighted/quantitative magnetic resonance imaging (dMRI/qMRI) to correlate the frequency and power of occipital alpha oscillations with the tissue properties of the OR by focusing on the different characteristics across individuals. We found that alpha frequency negatively correlated with intra-cellular volume fraction, reflecting diffusion properties in intracellular (axonal) space, whereas alpha power was not correlated with any tissue properties measurements. No significant correlation was found between OR and beta frequency/amplitude or between other white matter tract connecting parietal and inferotemporal cortex and alpha frequency/amplitude. These results support the hypothesis that an interaction between thalamic nuclei and early visual areas is essential for determining the occipital alpha oscillatory rhythm.

Significance Statement Alpha oscillations, the most salient neural oscillations in the human brain, are known to be involved in various types of perception. The frequency of occipital alpha oscillations varies across participants, but the underlying structures regulating this variability remain unknown. We combined MEG measurements with diffusion and quantitative MRI measurements and found that frequency properties of intrinsic occipital alpha oscillations correlated with a tissue property of the optic radiation (OR), a white matter tract connecting the lateral geniculate nucleus and primary visual cortex. This result supports the idea that thalamocortical interactions mediate the properties of intrinsic occipital alpha oscillations.