Doug Altshuler

As an animal moves through the world, images of surfaces and edges in the environment move across the retina, a visual signal known as optic flow. All vertebrates have a rapid pathway for optic flow encoding. In birds, the axons of retinal ganglion cells project to two regions in the midbrain, the lentiformis mesencephali (LM) and the nucleus of the basal optic root (nBOR) that respond only to optic flow signals. In mammals, these regions are called the nucleus of the optic tract and the terminal nuclei, respectively. The optic flow information is transmitted to several pre-motor regions in the hindbrain including the inferior olive, the vestibulocerebellum, and the oculomotor cerebellum. The circuitry has a well-known role in stabilizing eye movements and has been thought to be highly conserved across tetrapods. In contrast to this idea, our laboratory has found that the anatomy of the midbrain optic flow circuit, its neural response properties, and visual guidance strategies vary considerably among bird species. Some of this variation appears to be explained by differences in species visual ecology and mode of locomotion. Collectively, our work is focused on testing the hypothesis that the midbrain optic flow pathway also controls stabilization of the whole body, and the inverse function, maneuverability in response to salient visual signals. We apply approaches in neurophysiology, neuroanatomy, biomechanics, and behaviour.