Visual evoked potentials in the forebrain of the pigeon

Abstract

The telencephalon of anaesthetized pigeons was systematically explored for flash evoked potentials. A short latency projection to the hyper striatum was confirmed. A second short latency projection which appears to have a major focus in the medial sector of the neostriatum caudale and a more diffuse representation in the remainder of this structure was also found. Longer latency responses were found in a band of tissue surrounding the ectostriatum although the latency of these potentials was too short to be compatible with their origin in a projection from the thalamic nucleus rotundus. The core of the ectostriatum was not responsive under the conditions of the present study. A previously reported projection to the avian archistriatum was not confirmed and evidence is presented that supposed evoked potentials in this region of the brain were confused with volume conducted electroretinograms. All forebrain evoked potentials were attenuated by repetition rates above 1 hz. The origin of these projections is discussed in conjunction with evoked potentials recorded at lower levels of the pigeon's visual system under the same conditions and in the light of available anatomical and electrophysiological evidence. It is concluded that the information about visual projections to the avian forebrain is as yet too incomplete to be useful as evidence for presumptive avian-mammalian forebrain homologies.