A CENTRIFUGALLY CONTROLLED CIRCUIT IN THE AVIAN RETINA AND ITS POSSIBLE ROLE IN VISUAL-ATTENTION SWITCHING

The isthmo-optic nucleus (ION) is the main source of efferents to the retina in birds. Isthmo-optic neurons project in topographical order o n amacrine cells in the ventral parts of the retina, and a subclass of these known as proprioretinal neurons project onto the dorsal retina. We propose that, through the intermediary of the amacrine target cell s, activity in the isthmo-optic pathway excites ganglion cells locally in the ventral retina but inhibits those in dorsal regions. This circ uit would thereby mediate centrifugally controlled switches in attenti on between the dorsal retina, involved in feeding, and the more ventra l parts, involved in scanning for predators. This hypothesis accounts for a wide range of disparate data from behavior, comparative anatomy, endocrinology, hodology, and neurophysiology.