Slide 35

Fluorescent tracers injected into both optic tecta of the owl. Labeled cortico-tectal and retinotectal neurons can be studied after allowing for time for the tracer to be transported retrogradely from the injection site. One remarkable finding is that these anterior regions of the tectum receive projections from BOTH sides of the brain, but that there are very few neurons that project individually to both sides. Ipsi- and contra-projecting neurons are found side by side in the same cortical location, but there are virtually no double-labelld neurons. This conundrum was solved when it was discovered that the corticotectal projection is segregated into bands representing the two hemispheres. Although this arrangement looks like the ocular dominance arrays of primate visual cortex and three-eyed frog tectum, note that in this case, each stripe represents the HEMISPHERE OF ORIGIN of the innervating fibres, not the EYE OF ORIGIN. (Owl corticotectal neurons are exquisitely binocular).

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