Attentional control of the avian retina

Abstract

Retina receives centrifugal projection from the brain, and it is suggested that retinal function is somehow modulated, depending on the internal state of the brain. In birds, it is known that (1) most neurons in the isthmo-optic nucleus (ION) send their axons to the contralateral retina, (2) the retinopetal projection is organized topographically and (3) activity of isthmo-optic (IO) neurons enhances visual responses of the retinal ganglion cells. To clarify the functional significance of this pathway, we recorded spikes of IO neurons in awake Japanese quails with unrestrained heads using an implanted electrode assembly, while recording head movements with a high-speed video camera. The IO neurons fire passively by applying visual stimuli to their receptive fields and voluntarily without visual stimuli or eye-head movements. Voluntary activity was observed not only in the middle of eye-head fixation but also during about 200 ms before the onset of head saccades. The intensity of the activity before the onset of head saccades depended predominantly on the direction of motion in which the head saccades is initiated. That is, the IO neurons showed a large phasic elevation of activity before the onset of head saccades toward their receptive field, but substantially less response before the onset of head saccades in other directions. The IO neurons may convey signals reflecting covert spatial attention, which precedes overt attention shifts, to the retina, and that retinal local output may be enhanced by centrifugal signals before gaze shifts in a topographical manner specific to the direction of motion. [J Physiol Sci. 2007;57 Suppl:S11]