Development of flash-evoked responses in the ectostriatum of the zebra finch: an evoked potential and current-source-density analysis.

The morphological development of the tectofugal pathway in the zebra finch has recently been described in a series of studies from our laboratory. No data are currently available on the development of visual responsiveness in this pathway. We therefore investigated the development of visually evoked potentials (VEPs) in the ectostriatum, the telencephalic target area of the tectofugal pathway. Contralateral VEPs could already be recorded in 20-day-old birds, whereas ipsilateral VEPs could first be recorded in 40-day-old birds. The latencies of contralateral VEPs decrease to adult values between 20 and 40 days of age, probably due to an increase in the myelination of afferent fibers. The amplitudes of the contralateral VEPs increase continuously from day 20 to day 60; however, between 60 and 80 days of age the responses diminish substantially (-60%). Thus, contralateral VEPs in 80-day-old birds are not significantly different from those in 20-day-old birds. Thereafter the responses recover and reach their final amplitude values at about 150 days of age. The relationship of these results to morphological studies and possible mechanisms which may cause the double-peaked development of visual-evoked potentials in the ectostriatum are discussed.