Visual Stimuli Induce Waves of Electrical Activity in Turtle Cortex

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 94; no. 14; pp. 7621 - 7626
• Main Authors: Prechtl, J. C., Cohen, L. B., Pesaran, B., Mitra, P. P., Kleinfeld, D.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 08.07.1997; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences of the USA
• Subjects: Animals; Biological Sciences; Cats; Cerebral Cortex - physiology; Cognition & reasoning; Demodulation; Depolarization; Dyes; Electrodes; Electrophysiology; Eyes & eyesight; Freshwater; Medical research; Neurobiology; Neurology; Neurons; Photic Stimulation; Pixels; Pseudemys scripta; Turtles; Turtles - physiology; Visible spectrum; Vision, Ocular - physiology; Visual cortex; Visual stimulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.14.7621

The computations involved in the processing of a visual scene invariably involve the interactions among neurons throughout all of visual cortex. One hypothesis is that the timing of neuronal activity, as well as the amplitude of activity, provides a means to encode features of objects. The experimental data from studies on cat [Gray, C. M., Konig, P., Engel, A. K. & Singer, W. (1989) Nature (London) 338, 334-337] support a view in which only synchronous (no phase lags) activity carries information about the visual scene. In contrast, theoretical studies suggest, on the one hand, the utility of multiple phases within a population of neurons as a means to encode independent visual features and, on the other hand, the likely existence of timing differences solely on the basis of network dynamics. Here we use widefield imaging in conjunction with voltage-sensitive dyes to record electrical activity from the virtually intact, unanesthetized turtle brain. Our data consist of single-trial measurements. We analyze our data in the frequency domain to isolate coherent events that lie in different frequency bands. Low frequency oscillations (<5 Hz) are seen in both ongoing activity and activity induced by visual stimuli. These oscillations propagate parallel to the afferent input. Higher frequency activity, with spectral peaks near 10 and 20 Hz, is seen solely in response to stimulation. This activity consists of plane waves and spiral-like waves, as well as more complex patterns. The plane waves have an average phase gradient of ≈ π /2 radians/mm and propagate orthogonally to the low frequency waves. Our results show that large-scale differences in neuronal timing are present and persistent during visual processing.