The variability of the maintained discharge of cat dorsal lateral geniculate cells.

Abstract

SUMMARY1. Maintained discharge in the presence of a steady background luminance was analysed from forty-eight cells in the A laminae of the dorsal lateral geniculate nucleus ofcat. Cells were categorized as XG or YG and, in most cases, as on-or off-centre. The temporal contrast sensitivity function of twenty-seven of the cells was measured using drifting gratings of the optimal spatial frequency.2. The maintained discharge was characterized by several simple descriptors, including the interval distribution, mean firing rate, and coefficient of variability. Its temporal organization was revealed by two indicators of correlational properties, the normalized autocovariance and the serial correlogram, and more effectively, by the less familiar plot of the standard deviation of firing rate versus sample duration.3. The statistics revealing temporal organization of the maintained discharge indicated that the variability of firing was nearly, but not quite, derived from a renewal process. The maintained discharges of seven cells were studied for more than one luminance level. Mean luminance did not appear to have any consistent effect upon the statistics of the maintained discharge.4. The temporal filtering properties of lateral geniculate cells were deduced from a comparison of the temporal contrast sensitivities of geniculate neurones (Troy, 1983b) and retinal ganglion cells (Lennie, 1980). Analyses showed that the maintained discharge of retinal neurones passed through this filter could not account for the observed statistics of the maintained discharge of geniculate neurones.5. It is proposed that additional noise is added to the retinal signal at the level of the lateral geniculate. Models are presented to explain how the signals might be filtered in a way that does not also affect the added noise.

Tailoring of variability in the lateral geniculate nucleus of the cat

“…This variability is not evident in our perceptions of the visual world; either it is removed at later stages, or it is an integral part of the visual processing that leads to perception. Variability is greater at more central levels (Bishop et al 1964;Levine and Troy 1986;Wilson et al 1988;Hartveit and Heggelund 1994) and, as this report suggests, may be 'tailored' to serve some function.…”

“…The variability of firing that is generally studied is the variance of sustained discharges, firing in the absence of temporal changes in the visual stimulus (Kuffler et al 1957;Bishop et al 1964;Frishman and Levine 1983;Levine and Troy 1986;Levine 1987;Robson and Troy 1987;Wilson et al 1988). This is irrelevant in perception, for the visual image is in constant flux.…”

Fractal Features of Dark, Maintained, and Driven Neural Discharges in the Cat Visual System

“…This is true whether the retina is in the dark [1,2], or whether it is adapted to a stimulus of fixed luminance [3,4,5,6]. It is also true for time-varying visual stimuli such as drifting gratings.…”

The temporal resolution of neural codes: does response latency have a unique role?

“…As non-Poisson distributions of spike count have been reported in responses of neurons in the retina, lateral geniculate nucleus, V1, TE, parietal and frontal lobes (Tolhurst et al 1983;Levine & Troy 1986;Bradley et al 1987;Vogels et al 1989;Snowden et al 1992;Britten et al 1993;Victor & Purpura 1996;Berry et al 1997;Reich et al 1997;Baddeley et al 1997;Berry & Meister 1998;Gershon et al 1998;Buracas et al 1998;Lee et al 1998;Oram et al 1999aOram et al ,b, 2001), we introduced a new stochastic model (the SCM model; Oram et al 1999aOram et al ,b, 2001). The SCM model extended earlier models based on nonhomogenous Poisson processes by replacing the assumed Poisson distribution of spike counts with the observed frequency distribution of spike counts.…”