Callosal connections of primary visual cortex predict the spatial spreading of binocular rivalry across the visual hemifields

Erhan Genç

doi:10.3389/fnhum.2011.00161

Abstract

In binocular rivalry, presentation of different images to the separate eyes leads to conscious perception alternating between the two possible interpretations every few seconds. During perceptual transitions, a stimulus emerging into dominance can spread in a wave-like manner across the visual field. These traveling waves of rivalry dominance have been successfully related to the cortical magnification properties and functional activity of early visual areas, including the primary visual cortex (V1). Curiously however, these traveling waves undergo a delay when passing from one hemifield to another. In the current study, we used diffusion tensor imaging (DTI) to investigate whether the strength of interhemispheric connections between the left and right visual cortex might be related to the delay of traveling waves across hemifields. We measured the delay in traveling wave times (ΔTWT) in 19 participants and repeated this test 6 weeks later to evaluate the reliability of our behavioral measures. We found large interindividual variability but also good test–retest reliability for individual measures of ΔTWT. Using DTI in connection with fiber tractography, we identified parts of the corpus callosum connecting functionally defined visual areas V1–V3. We found that individual differences in ΔTWT was reliably predicted by the diffusion properties of transcallosal fibers connecting left and right V1, but observed no such effect for neighboring transcallosal visual fibers connecting V2 and V3. Our results demonstrate that the anatomical characteristics of topographically specific transcallosal connections predict the individual delay of interhemispheric traveling waves, providing further evidence that V1 is an important site for neural processes underlying binocular rivalry.

Highlights

The phenomenon of binocular rivalry has been studied for almost 200 years (Wheatstone, 1838) and has recently inspired the search for the neural correlates of conscious perception (Logothetis, 1998; Tong, 2003)
In accordance with a previous paper (Dougherty et al, 2007), we found that axial diffusivity (AD) did not contribute significantly to ΔTWT prediction [r(17) = −0.35, p = 0.14], but there was a strong correlation with radial diffusivity (RD) [r(17) = −0.72 and p < 0.001; Figure 5]
We focused our analyses on RD because, in accordance with a previous study (Dougherty et al, 2007), we found that the first eigenvalue did not contribute to the correlation between microstructure and ΔTWT, which affects correlations with fractional anisotropy (FA)

Summary

Introduction

The phenomenon of binocular rivalry has been studied for almost 200 years (Wheatstone, 1838) and has recently inspired the search for the neural correlates of conscious perception (Logothetis, 1998; Tong, 2003). Using psychophysical estimates of wave speed for differently sized rival stimuli, Wilson et al (2001) found that these traveling waves of changing perceptual dominance spread over space with a characteristic speed well predicted by the cortical magnification factor for primary visual cortex (V1). In a series of follow-up studies, Lee et al (2005, 2007) used functional magnetic resonance imaging (fMRI) to demonstrate a neural correlate of traveling waves in early visual cortex (V1–V3) They found that peak activity along the cortical representation of the rival stimulus was systematically shifted in time, implying that traveling wave generation may arise within V1 as suggested by earlier psychophysical results

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