Evoked potential evidence for a stripe-rearing effect on rat visual cortex

Abstract

Restricting visual experience to lines of one orientation during development modifies visual cortex physiology in cats but not in rabbits. To test the importance of binocular convergence in this stripe-rearing species difference, hooded rats, which, like the rabbit, have a highly decussated visual system, were studied. Subjects were reared in darkness and binocularly exposed, for 25 to 40 h during the 3rd to 7th weeks after birth, to a visual field of vertical or horizontal stripes. Visual cortical evoked potentials to stroboscopically illuminated vertical and horizontal stripe stimuli were recorded during the 8th week. The relative amplitude of the early positive component of the visually evoked potential was greater for stimuli matching the rearing orientation than for stimuli of the opposite orientation. Evoked responses to stimuli of other orientations were generally smaller than those to the exposure orientation. In rats reared in normal cyclic light or in total darkness, there were no differences in the response to vertical vs. horizontal stripe stimuli. The results indicate that evoked potentials are modified by developmental restriction of experience to oriented contours without differential input to the eyes in an organism with limited binocular convergence.