A parvocellular-magnocellular functional gradient in human visual cortex

ABSTRACT The magnocellular and parvocellular systems are major visual recognition pathways, with distinct histological and physiological properties. Despite their critical role, there is limited evidence on the specific contributions these visual pathways make to visual recognition in general and to word reading in particular. Using a multimodal functional MRI approach and individual-subject analyses, here we investigate the involvement of visual cortex regions in the recognition of magnocellular- and parvocellular-biased words and images. Our results reveal a functional gradient in the activation profile of both left and right visual cortex: posterior regions are more strongly recruited for processing parvocellular-biased, while anterior regions are more involved in processing magnocellular-biased stimuli. Furthermore, functional connectivity analyses show clustering in the strength of functional coupling among visual cortex regions as a function of the distance between regions, with greater coupling within and less coupling across posterior and anterior regions. Finally, we found minimal differences in lateralization for word and image recognition in these visual cortical regions. These results were replicated in a retest session with a subset of participants. Our findings underscore a functional division of labor in the visual cortex as a function determined by a parvocellular or magnocellular bias in properties of the stimuli and further reveal that in this context the visual cortex is not particularly biased towards words or images.