title: Temporal Asymmetry in Dark-Bright Processing Initiates Propagating Activity across Primary Visual Cortex.
abstract: Differences between visual pathways representing darks and lights have been shown to affect spatial resolution and detection timing. Both psychophysical and physiological studies suggest an underlying retinal origin with amplification in primary visual cortex (V1). Here we show that temporal asymmetries in the processing of darks and lights create motion in terms of propagating activity across V1. Exploiting the high spatiotemporal resolution of voltage-sensitive dye imaging, we captured population responses to abrupt local changes of luminance in cat V1. For stimulation we used two neighboring small squares presented on either bright or dark backgrounds. When a single square changed from dark to bright or vice versa, we found coherent population activity emerging at the respective retinal input locations. However, faster rising and decay times were obtained for the bright to dark than the dark to bright changes. When the two squares changed luminance simultaneously in opposite polarities, we detected a propagating wave front of activity that originated at the cortical location representing the darkened square and rapidly expanded toward the region representing the brightened location. Thus, simultaneous input led to sequential activation across cortical retinotopy. Importantly, this effect was independent of the squares' contrast with the background. We suggest imbalance in dark-bright processing as a driving force in the generation of wave-like activity. Such propagation may convey motion signals and influence perception of shape whenever abrupt shifts in visual objects or gaze cause counterchange of luminance at high-contrast borders.
  
  
  CONCLUSIONS
  An elementary process in vision is the detection of darks and lights through the retina via ON and OFF channels. Psychophysical and physiological studies suggest that differences between these channels affect spatial resolution and detection thresholds. Here we show that temporal asymmetries in the processing of darks and lights create motion signals across visual cortex. Using two neighboring squares, which simultaneously counterchanged luminance, we discovered propagating activity that was strictly drawn out from cortical regions representing the darkened location. Thus, a synchronous stimulus event translated into sequential wave-like brain activation. Such propagation may convey motion signals accessible in higher brain areas, whenever abrupt shifts in visual objects or gaze cause counterchange of luminance at high-contrast borders.
authors: Optical Imaging Group, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany.
authors: Sascha
authors: http://orcid.org/0000-0002-3651-6143
authors: S
authors: Rekauzke
authors: Optical Imaging Group, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany.
authors: Nora
authors: N
authors: Nortmann
authors: Optical Imaging Group, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany.
authors: Robert
authors: http://orcid.org/0000-0002-0067-3956
authors: R
authors: Staadt
authors: Department of Psychology, Florida Atlantic University, Boca Raton, Florida 33486, and.
authors: Howard S
authors: HS
authors: Hock
authors: Theory of Cognitive Systems, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany.
authors: Gregor
authors: http://orcid.org/0000-0002-4776-9998
authors: G
authors: Schöner
authors: Optical Imaging Group, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany, Theory of Cognitive Systems, Institut für Neuroinformatik, Ruhr University Bochum, 44801 Bochum, Germany dirk.jancke@rub.de.
authors: Dirk
authors: D
authors: Jancke
mesh_terms: D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D005556:Form Perception / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008027:Light; D008297:Male; D009039:Motion Perception / Q000502:physiology; D010775:Photic Stimulation; D011601:Psychophysics; D012160:Retina / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*
keywords: ON/OFF visual pathways; luminance counterchange; motion encoding; propagating activity; visual cortex; voltage-sensitive dye imaging