The relation of visual field defects to retinotectal topography in teleost fish

Abstract

Classical heart rate conditioning was employed for mapping the location and extent of scotomata due to surgical lesions in the optic tectum of a marine teleost, Girella nigricans (Ayres). The resulting maps of the visual field were compared with subsequently obtained maps of the retinotectal projection by electrophysiological techniques. The results reveal a strict parallel between anatomical orderliness of the retinal projection upon the midbrain tectum and functional vision. A small lesion in the optic tectum abolishes vision in a specific area of the visual field which is related to the site of the lesion in conformity with the electrophysiologically determined projection pattern. The areas of the visual field noted by an absence of the conditioned cardiac response were found to be larger than the unresponsive area determined by electrophysiological methods. Extensive lesions in the dorsum of the tectum resulted in a superior horizontal hemianopia when mapped by the cardiac conditioned response several days after surgery. The electrophysiologically unresponsive areas appear to be due to local surface damage caused by the lesion, added to by interruption of passing optic fibers, whereas the large field defects determined by the conditioned response perimetry seem to be so much larger, principally due to additional destruction in the tectal neuropil, sometimes also due to occasional section of efferent fiber tracts. Regeneration with restitution of vision was observed 50 days after a lesion restricted to the superficial tectal layers.