Investigating the role of M and P pathways in the human brain during binocular rivalry

Abstract

When two sufficiently different stimuli are presented to each eye, perception alternates between them. Known as binocular rivalry, it is an example where visual consciousness needs to resolve a competition. Here, I aimed at investigating the neural mechanism behind this phenomenon, focusing on the contribution of the two visual pathways. Magnocellular (M) and Parvocellular (P) pathways are two information processing streams whose functions have been informative to explain many visual phenomena and clinical disorders. In the lateral geniculate nucleus (LGN), the M and P neurons are disjoint in a layered structure, receiving input from a single eye. Using magnetic resonance imaging (MRI), my goal was to identify the M and P layers in the LGN and examine the rivalry-related eye-specific responses within these layers. Series of techniques and analyses revealed that quantitative MRI is promising to identify the M and P layers in the LGN while functional MRI with monocular eye stimulation results in a clustered eye-specific structure and is not useful to separate the eye- specific regions into M and P sections. However, unsupervised approximation of the data with non-negative matrix factorization provided more consistent eye-specific structure than the generalized linear model. In the investigation of binocular rivalry, achromatic gratings induced rivalry that was represented in the eye-specific layers, and overall rivalry magnitude was similar in the M and P sections. These results highlight the importance of design and analysis in the functional imaging of the LGN layers and contributes to the binocular rivalry literature by showing the perceptual resolution in the LGN with achromatic stimuli and within M and P sections.