The dynamic nonlinear behavior of fly photoreceptors evoked by a wide range of light intensities.
Fly photoreceptor cells were stimulated with steps of light over a wide intensity range. First- and second-order Volterra kernels were then computed from sequences of combined step responses. Diagonal values of the second-order Volterra kernels were much greater than the off-diagonal values, and the diagonal values were roughly proportional to the corresponding first-order kernels, suggesting that the response could be approximated by a static nonlinearity followed by a dynamic linear component (Hammerstein model). The amplitudes of the second-order kernels were much smaller in light-adapted than in dark-adapted photoreceptors. Hammerstein models constructed from the step input/output measurements gave reasonable approximations to the actual photoreceptor responses, with light-adapted responses being relatively better fitted. However, Hammerstein models could not account for several features of the photoreceptor behavior, including the dependence of the step response shape on step amplitude. A model containing an additional static nonlinearity after the dynamic linear component gave significantly better fits to the data. These results indicate that blowfly photoreceptors have a strong early gain control nonlinearity acting before the processes that create the characteristic time course of the response, in addition to the nonlinearities caused by membrane conductances.
French
A S
AS
Department of Physiology, University of Alberta, Edmonton, Canada.
Korenberg
M J
MJ
Järvilehto
M
M
Kouvalainen
E
E
Juusola
M
M
Weckström
M
M
D000818:Animals; D003624:Darkness; D004175:Diptera; D008027:Light; D008433:Mathematics; D008959:Models, Neurological; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000528:radiation effects