Abstract
Magnocellular versus parvocellular (M-P) streams are fundamental to the organization of macaque visual cortex. Segregated, paired M-P streams extend from retina through LGN into V1. The M stream extends further into area V5/MT, and parts of V2. However, elsewhere in visual cortex, it remains unclear whether M-P-derived information (1) becomes intermixed or (2) remains segregated in M-P-dominated columns and neurons. Here we tested whether M-P streams exist in extrastriate cortical columns, in 8 human subjects (4 female). We acquired high-resolution fMRI at high field (7T), testing for M- and P-influenced columns within each of four cortical areas (V2, V3, V3A, and V4), based on known functional distinctions in M-P streams in macaque: (1) color versus luminance, (2) binocular disparity, (3) luminance contrast sensitivity, (4) peak spatial frequency, and (5) color/spatial interactions. Additional measurements of resting state activity (eyes closed) tested for segregated functional connections between these columns. We found M- and P-like functions and connections within and between segregated cortical columns in V2, V3, and (in most experiments) area V4. Area V3A was dominated by the M stream, without significant influence from the P stream. These results suggest that M-P streams exist, and extend through, specific columns in early/middle stages of human extrastriate cortex.SIGNIFICANCE STATEMENT The magnocellular and parvocellular (M-P) streams are fundamental components of primate visual cortical organization. These streams segregate both anatomical and functional properties in parallel, from retina through primary visual cortex. However, in most higher-order cortical sites, it is unknown whether such M-P streams exist and/or what form those streams would take. Moreover, it is unknown whether M-P streams exist in human cortex. Here, fMRI evidence measured at high field (7T) and high resolution revealed segregated M-P streams in four areas of human extrastriate cortex. These results suggest that M-P information is processed in segregated parallel channels throughout much of human visual cortex; the M-P streams are more than a convenient sorting property in earlier stages of the visual system.
Highlights
In macaque monkeys, different visual features are processed in functionally and anatomically segregated streams
These results suggest that magnocellular and parvocellular (M-P) information is processed in segregated parallel channels throughout much of human visual cortex; the M-P streams are more than a convenient sorting property in earlier stages of the visual system
Multiple classic neurobiological techniques have revealed a fundamental and elegant segregation of information processing within magnocellular (M) versus parvocellular (P) streams, in the retina, LGN, and striate cortex, with M-stream influence extending to area MT
Summary
Different visual features are processed in functionally and anatomically segregated streams. Example includes the magnocellular versus parvocellular (M-P) streams, which extend in parallel from retina through early visual cortex (Fig. 1) (Hubel and Livingstone, 1987; Zeki and Shipp, 1988; Felleman and Van Essen, 1991; Merigan and Maunsell, 1993). The M and P LGN layers project into V1 layers 4C␣, and 4C, respectively. From V1 to V2, it is controversial whether M and P streams remain segregated and parallel (Hubel and Livingstone, 1987; Livingstone and Hubel, 1987) or whether they are rerouted into a different set of segregated projections, the blobs/patches and interblobs/interpatches (Sincich and Horton, 2002, 2005a, b)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.