Scotopic Vision Is Selectively Processed in Thick-Type Columns in Human Extrastriate Cortex

Abstract

In humans, visual stimuli can be perceived across an enormous range of light levels. Evidence suggests that different neural mechanisms process different subdivisions of this range. For instance, in the retina, stimuli presented at very low (scotopic) light levels activate rod photoreceptors, whereas cone photoreceptors are activated relatively more at higher (photopic) light levels. Similarly, different retinal ganglion cells are activated by scotopic versus photopic stimuli. However, in the brain, it remains unknown whether scotopic versus photopic information is: 1) processed in distinct channels, or 2) neurally merged. Using high-resolution functional magnetic resonance imaging at 7 T, we confirmed the first hypothesis. We first localized thick versus thin-type columns within areas V2, V3, and V4, based on photopic selectivity to motion versus color, respectively. Next, we found that scotopic stimuli selectively activated thick- (compared to thin-) type columns in V2 and V3 (in measurements of both overlap and amplitude) and V4 (based on overlap). Finally, we found stronger resting-state functional connections between scotopically dominated area MT with thick- (compared to thin-) type columns in areas V2, V3, and V4. We conclude that scotopic stimuli are processed in partially segregated parallel streams, emphasizing magnocellular influence, from retina through middle stages of visual cortex.

Two interdigitated fine-scale channels for encoding motion and stereopsis within the human magnocellular stream

“…Using advanced technologies and the state-of-the-art scanners, many groups have revealed mesoscale structures within the spatial scale of cortical columns in human striate 28,74,75 and extrastriate cortex 28,[30][31][32] . For understandable reasons, these studies typically limited A schematic representation of the stimuli is also illustrated on top of each panel (see Online Methods).…”

“…Previously we showed evidence for selective functional connectivity between “stereo-vs. color-selective” 28 and “motion-vs. color-selective” 31 sites. Here, we extend those findings by showing that such a selective functional connection also exists between “motion-vs. stereo-selective” sites (Figure 6).…”

“…With recent advances in high-resolution neuroimaging techniques, homologous columnar organizations have been shown in human visual cortex. Specifically, multiple studies have shown evidence for cortical columns across areas V2, V3 and V3A that contribute to encoding stereopsis 28-30 and motion 31, 32 . Similar to NHPs, and based on their stimulus selectivity and functional connections, these cortical columns appear to be under the influence of magnocellular stream 2, 31 .…”

“…Specifically, multiple studies have shown evidence for cortical columns across areas V2, V3 and V3A that contribute to encoding stereopsis 28-30 and motion 31, 32 . Similar to NHPs, and based on their stimulus selectivity and functional connections, these cortical columns appear to be under the influence of magnocellular stream 2, 31 . Here again, the relative organization of motion-and stereo-selective sites within the early visual areas remains largely unknown due to technical challenges in functional imaging of such small brain sites.…”

Escaping the nocturnal bottleneck, and the evolution of the dorsal and ventral streams of visual processing in primates

“…The M celldominated output layers of V1 then activate modules in V2, and likely in V3, that project to MT [157]. Thus, MT neurons appear to reflect only M cell activity [158,159]. Yet, M and P ganglion cells in the retina are responsive to both rods and cones.…”