Columnar Segregation of Magnocellular and Parvocellular Streams in Human Extrastriate Cortex

• Published in: The Journal of neuroscience Vol. 37; no. 33; pp. 8014 - 8032
• Main Authors: Tootell, Roger B.H., Nasr, Shahin
• Format: Journal Article
• Language: English
• Published: United States Society for Neuroscience 16.08.2017
• Subjects: Adult; Animals; Binocular vision; Color; Color vision; Eye (anatomy); Female; Frequency dependence; Functional magnetic resonance imaging; Humans; Macaca fascicularis; Magnetic Resonance Imaging - methods; Male; Monkeys & apes; Photic Stimulation - methods; Retina; Streams; Visual cortex; Visual Cortex - cytology; Visual Cortex - physiology; Visual Pathways - cytology; Visual Pathways - physiology; Visual task performance; Young Adult; high-resolution fMRI; cortical hierarchy; stereopsis; color; spatial frequency; contrast sensitivity
• ISSN: 0270-6474; 1529-2401; 1529-2401
• DOI: 10.1523/JNEUROSCI.0690-17.2017

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. 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.