Visual Stimuli Induce Waves of Electrical Activity in Turtle Cortex Turtle Cortex

Wave propagation is a hallmark of physical, chemical and biological systems with oscillatory dynamics. Yet in nervous systems such waves have only been characterized in invertebrate and subcortical networks. Here we use widefield imaging in conjunction with voltage sensitive dyes to record electrical activity from the virtually intact, unanesthetized turtle brain. We identify oscillations that propagate throughout cortex in both ongoing activity and activity induced by visual stimuli. Low frequency oscillations (,5 Hz) have the largest amplitude and propagate parallel to the afferents to visual cortex. Higher frequency activity, with spectral peaks near 10 and 20 Hz, consists of plane waves and spiral-like waves, as well as more complex patterns. The plane waves have an average phase gradient of ~ pi /2 radians/mm and propagate orthogonally to the low frequency waves. Our results show that large-scale spatiotemporal patterns of activity, whose form cannot be predicted from the underlying neuronal architecture, are present during normal cortical function.