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Published May 1, 1996 | public
Journal Article

Comparison of discharge variability in vitro and in vivo in cat visual cortex neurons


1. In neocortical slices, the majority of neurons fire quite regularly in response to constant current injections. But neurons in the intact animal fire irregularly in response to constant current injection as well as to visual stimuli. 2. To quantify this observation, we developed a new measure of variability, which compares only adjacent interspike intervals and is therefore less sensitive to rate variations than existing measures such as the coefficient of variation of interspike intervals. 3. We find that the variability of firing is much higher in cells of primary visual cortex in the anesthetized cat than in slice. The response to current injected from an intracellular electrode in vivo is also variable, but slightly more regular and less bursty than in response to visual stimuli. 4. Using a new technique for analyzing the variability of integrate-and-fire neurons, we prove that this behavior is consistent with a simple integrate-and-fire model receiving a large amount of synaptic background activity, but not with a noisy spiking mechanism.

Additional Information

Copyright © 1996 the American Physiological Society. We thank B. Ahmed, N. Berman, and K. Martin for providing the data we analyzed. The research reported here was supported by the Office of Naval Research, the National Institute of Mental Health (through the Center for Cell and Molecular Signaling and a direct grant to C. Koch), the National Science Foundation, the Medical Research Council of the United Kingdom, and Imperial College in London. Gary Holt was supported by a National Defense Science and Engineering Graduate Fellowship and a grant from the Sloan Center for Theoretical Neurobiology. Rodney Douglas was supported by the Gatsby Foundation.

Additional details

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