Unusual postnatal development of visually evoked potentials in four brain areas of white zebra finches

The central visual system of white zebra finches is physiologically different from normally coloured (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in the white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. The present study shows that the enhancement of ipsilateral responses in white zebra finches is detectable in all areas of the tectofugal pathway, and also in the visual wulst, the only station of the thalamofugal pathway examined so far in white zebra finches. In all investigated areas, the enhancement is already obvious at 20 days after hatching, the earliest age that allows reliable recordings. A deficit in inhibition of ipsilateral stimuli, probably combined with a general increase in the number of ipsilateral projections, may cause the observed enhancements of ipsilateral responses in white birds.