Improved estimates for the role of grey matter volume and GABA in bistable perception

Kristian Sandberg,Jakob Udby Blicher,Simon Hviid Del Pin,Lau Møller Andersen,Geraint Rees,Ryota Kanai

doi:10.1016/j.cortex.2016.08.006

Abstract

Across a century or more, ambiguous stimuli have been studied scientifically because they provide a method for studying the internal mechanisms of the brain while ensuring an unchanging external stimulus. In recent years, several studies have reported correlations between perceptual dynamics during bistable perception and particular brain characteristics such as the grey matter volume of areas in the superior parietal lobule (SPL) and the relative GABA concentration in the occipital lobe. Here, we attempt to replicate previous results using similar paradigms to those used in the studies first reporting the correlations. Using the original findings as priors for Bayesian analyses, we found strong support for the correlation between structure-from-motion percept duration and anterior SPL grey matter volume. Correlations between percept duration and other parietal areas as well as occipital GABA, however, were not directly replicated or appeared less strong than previous studies suggested. Inspection of the posterior distributions (current “best guess” based on new data given old data as prior) revealed that several original findings may reflect true relationships although no direct evidence was found in support of them in the current sample. Additionally, we found that multiple regression models based on grey matter volume at 2–3 parietal locations (but not including GABA) were the best predictors of percept duration, explaining approximately 35% of the inter-individual variance. Taken together, our results provide new estimates of correlation strengths, generally increasing confidence in the role of the aSPL while decreasing confidence in some of the other relationships.

Highlights

Across a century or more, ambiguous stimuli have been studied scientifically because they provide a method for studying the internal mechanisms of the brain while keeping the external stimulus constant
We examined how well the percept duration during structure from motion (SFM) perception was predicted from grey matter (GM) volume in particular areas of the superior parietal lobule (SPL) as well as from occipital gamma aminobutyric acid (GABA) concentration, as previous studies (Kanai et al, 2011, 2010; van Loon et al, 2013) had reported such relationships
When using frequentist statistics testing for significant correlations, we found direct support for the role of the exact anterior SPL coordinate reported

Summary

Introduction

Across a century or more, ambiguous stimuli have been studied scientifically because they provide a method for studying the internal mechanisms of the brain while keeping the external stimulus constant. Inhibitory (GABAergic) neurons may have a key role relating to cross-inhibition between representations in multiple models of bistable perception (e.g., Noest, van Ee, Nijs, & van Wezel, 2007; Wilson, 2003). The predictions of such models (e.g., Wilson, 2007) are consistent with a recent finding in an intermittent binocular rivalry magnetoencephalography (MEG) study (Sandberg, Barnes, et al, 2014). Across ten trials (of grating perception) before perception reversed to face perception, the amplitude of the face-specific M170 component increased, consistent with the prediction that adaptation of GABAergic neurons responsible for cross-adaptation lead to decreased suppression of the face stimulus. If reversals were related to random fluctuations or adaptation neurons representing the perceived stimulus, this modulation of activity related to the unperceived stimulus should not have been observed

Methods

Results

Conclusion