Visual capabilities and cortical maps in BALB/c mice.

By combining behavioural analyses with intrinsic signal optical imaging, we analysed visual performance and visual cortical activity in the albino mouse strain BALB/c, which is increasingly being used as an animal model of neuropsychological disorders. Visual acuity, as measured by a virtual-reality optomotor system, was 0.12 cycles per degree (cyc/deg) in BALB/c mice and 0.39 cyc/deg in pigmented C57BL/6 mice. Surprisingly, BALB/c mice showed reflexive head movements against the direction of the rotating stimulus. Contrast sensitivity was significantly lower in BALB/c mice (45% contrast at 0.064 cyc/deg) than in C57BL/6 mice (6% contrast). In the visual water task, visual acuity was 0.3 cyc/deg in BALB/c mice and 0.59 cyc/deg in C57BL/6 mice. Thus, the visual performance of BALB/c mice was significantly impaired in both behavioural tests - visual acuity was ∼ 0.3 cyc/deg lower than in C57BL/6 mice, and contrast sensitivity was reduced by a factor of ∼ 8. In BALB/c mice, visual cortical maps induced by stimulation of the contralateral eye were normal in both activation strength and retinotopic map quality. In contrast, maps induced by ipsilateral eye stimulation differed significantly between the strains - activity in a region representing 15° to 19° elevation in the visual field was significantly weaker in BALB/c mice than in C57BL/6 mice. Taken together, our observations show that BALB/c mice, like the albino animals of other species, have a significantly lower visual performance than C57BL/6 mice and a modified cortical representation of the ipsilateral eye that may impair stereopsis. Thus, our results caution against disregarding vision as a confounding factor in behavioural tests of neuropsychological disorders.