Circadian regulation of visually evoked potentials in the domestic pigeon,Columba livia

The avian circadian and visual systems are integrally related and together influence many aspects of birds' behavior and physiology. Certainly, light cycles and their visual perception are the major zeitgebers for circadian r hythms, but do circadian rhythms affect vision? To assess whether visual fu nction is regulated on a circadian basis, flash-evoked electroretinograms ( ERGs) and vision-evoked potentials (VEPs) from the optic tectum (TeO) were recorded simultaneously in domestic pigeons at different circadian phases i n a light-dark regime (LD) and in constant darkness (DD), while feeding act ivity was measured to determine circadian phase. In both LD and DD, the amp litudes of ERG b-waves were higher during the day than at night and latenci es of a- and b-waves were longer at night. The median effective intensity f or ERG a-wave was marginally higher during the day than during the night, i ndicating greater sensitivity at night, but this rhythm did not persist in DD. The amplitudes of TeO VEPs were also greater during the day, and latenc ies were greater at night in LD and DD. Together, the data indicate that a circadian clock regulates pigeon visual function at several integrative lev els.