Segregation of functionally distinct axons in the monkey's optic tract

Abstract

The classical neuro-ophthalmologic literature describes the organization of the primate's optic tract as containing a single topographic representation of the complete contralateral visual hemifield^1–4. In contrast, cats have separate visual field representations for the optic axons of the functionally distinct retinal ganglion cell classes^5,6. As the line of decussation for each ganglion cell class in the cat occupies a different location on the retinal surface^7–11, whereas in primates they are all superimposed¹², such a species difference might be expected. We report that implants of horseradish peroxidase placed in either the deep or superficial extremes of the monkey's optic tract produce retrograde labelling of distinct retinal ganglion cell classes, and produce anterograde labelling confined to distinct laminae of the lateral geniculate nucleus. Hence,the optic tract of the primate cannot contain a single representation of the contralateral visual hemifield; rather, independent visual field representations for the functionally distinct optic axons must exist. Their anatomical segregation may account for the clinical observation of selective impairments of distinct visual abilities following partial interruption of the optic tract in man¹³.