Connecting occipital alpha band peak frequency, visual temporal resolution, and occipital GABA levels in healthy participants and hepatic encephalopathy patients

Abstract

Recent studies have proposed a connection between the individual alpha band peak frequency and the temporal resolution of visual perception in healthy human participants. This connection rests on animal studies describing oscillations in the alpha band as a mode of phasic thalamocortical information transfer for low-level visual stimuli, which critically relies on GABAergic interneurons. Here, we investigated the interplay of these parameters by measuring occipital alpha band peak frequency by means of magnetoencephalography, visual temporal resolution by means of behavioral testing, and occipital GABA levels by means of magnetic resonance spectroscopy. Importantly, we investigated a sample of healthy participants and patients with varying grades of hepatic encephalopathy, which are known to exhibit decreases in the investigated parameters, thus providing an increased parameter space. We found that occipital alpha band peak frequency and visual temporal resolution were positively correlated, i.e., higher occipital alpha band peak frequencies were on average related to a higher temporal resolution. Likewise, occipital alpha band peak frequency correlated positively with occipital GABA levels. However, correlations were significant only when both healthy participants and patients were included in the analysis, thereby indicating a connection of the measures on group level (instead of the individual level). These findings provide new insights into neurophysiological and neurochemical underpinnings of visual perception.

Keywords: Alpha oscillations; CFF, Critical flicker frequency; CSD, Cross-spectral density; EC, Eyes-closed; ECG, Electro-cardiogram; EO, Eyes-open; EOG, Electro-oculogram; GABA; GABA+/Cr, GABA-to creatine -ratio; GABA, γ-aminobutyric acid; HE, Hepatic encephalopathy; HE1, Clinically manifest HE grade 1; HPI, Head position indication; Hepatic encephalopathy; ICA, Independent component analysis; MEG, Magnetoencephalography; MNI, Montreal Neurological Institute; MRS, Magnetic resonance spectroscopy; Magnetic resonance spectroscopy; Magnetoencephalography; Peak frequency; mHE, Minimal HE.

Fig. 1

Individual occipital alpha band peak frequencies in the eyes-closed (EC) condition (A), CFF (B) and occipital GABA+/Cr levels (C) separated by group. Each data point represents data for a single subject.

Fig. 2

Group-level average alpha band peak frequency source power distributions for the eyes-closed (EC) condition displayed on the MNI template brain for healthy controls (A), mHE patients (B), and HE1 patients (C). Source power estimates at each grid point are corrected for the noise estimate of the respective grid point (please see the Materials and methods part for further details). Color bars depict arbitrary units (a.u.) and uniformly apply to all three images.

Fig. 3

Scatterplots for individual occipital alpha band peak frequency for the eyes-closed (EC) condition as a function of CFF (A) and occipital GABA+/Cr levels (B). Correlations between occipital alpha band peak frequency and CFF were corrected for age. Correlations between occipital alpha band peak frequency and occipital GABA+/Cr levels were corrected for age and gray matter volume within the occipital MRS voxel. Insets show the regression line (straight line) and the 95% confidence intervals for the mean (dotted lines).