We previously showed that several visual behaviors required visual cortex...
but one visual task did not require V1
"We present data from one highly informative subject that learned several visual tasks and then received a bilateral lesion ablating 90% of primary visual cortex. After the lesion, this subject had a profound and persistent deficit in complex image discrimination, orientation discrimination, and full-field optic flow motion discrimination, compared with both pre-lesion performance and sham-lesion controls. Performance was intact, however, on another visual two-alternative forced-choice task that required approaching a salient visual target. [...] Taken together, our data provide evidence that these image, orientation, and motion discrimination tasks require primary visual cortex in the Long-Evans rat, whereas approaching a salient visual target does not." Sarah Petruno, Robert E Clark, and Pamela Reinagel (2013) PLoS One 8(2):e56543.(see the behavioral data below)
The ongoing interest in the lab is the nature of visually guided behaviors that bypass V1, otherwise known as "Blindsight". We hypothesize that blindsight in humans and V1-independent visual behavior in rats are supported by the retinal projections to the superior colliculus although a role for direct projections of the LGN to higher visual cortical areas in rat has not been ruled out. We presume that collicular and thalamocortical pathways are normally both active in intact vision, suggest that they have different computational advantages and weaknesses, and are interested in learning how these parallel pathways vie for control of behavior.
Retinal projections from one eye primarily to the contralateral superior colliculus in a Long Evans rat. Retinal axons were labeled with cholera toxin subunit b and visualised in dark field (Claire Discenza, unpub.)
Cajal's illustration showing the direct retinal projections to the SC in parallell with the thalamocortical pathway.
Daily performance on four visually guided tasks during training (above) and after a complete lesion to primary visual cortex (below). Colors indicate tasks as follows: Approach Salient Visual Target, with statue target (red) or with grating target (magenta); Image Discrimination (blue); Random Dot Motion Discrimination (green, cyan); and Orientation Discrimination (black).
|After removal of V1, the rat's performance on the approach tasks was not only intact but continued to improve with practice. Figures from Petruno, Clark and Reinagel (2013) PLoS One 8(2):e56543.|
For videos of normal rats performing the image and motion tasks, click icons below.
Image credit: the icon of the rollerskating mouse came from www.zebracorn.com