Statistical properties of the maintained discharge of chemically isolated ganglion cells in goldfish retina

Variability in the firing of retinal ganglion cells of goldfish: a review

The isolated retina of the goldfish has proven a valuable resource for studying the variability of firing of retinal ganglion cells. Three major areas of study are considered here: the variability of maintained discharges, the correlated firing of neighboring ganglion cells, and the variability of responses to light. The sources of variability, its relationship to retinal processing, and its possible functional role in perception are examined through these three aspects of variability. The results are related to similar studies in mammals (mainly cats). This retrospective is biased toward my studies over 30 years.

The potential coding utility of intercell cross-correlations in the retina

The action potentials (impulses) produced by pairs of neighboring retinal ganglion cells often show a tendency either to fire in close temporal synchrony or to avoid temporal synchrony. This cross-correlation (a rate of "coincidences" that differs from that expected by chance) has been exploited as a window into retinal processing, but its possible functional significance has proven elusive. Previous work has failed to show that the coincidences serve as a direct code for visual stimuli. In this analysis it is shown that the coincidences serve neither as a key for reducing variability nor as a key for improving the coding by the individual cells. The residual impulse trains (trains with coincidences deleted) are more variable than the raw impulse trains and provide an inferior coding to that of the raw impulse trains. There is negative correlation between the firing rate of the residual impulse trains and that of the coincidence impulse trains, which is consistent with the lower variance of the raw impulse trains. There is no consistent cross-correlation between the rates of residual impulse trains of cells in pairs showing cross-correlation; however, it is found that this observation does not discriminate among models for generating coincidences.

Reliability of spike timing in neocortical neurons

It is not known whether the variability of neural activity in the cerebral cortex carries information or reflects noisy underlying mechanisms. In an examination of the reliability of spike generation using recordings from neurons in rat neocortical slices, the precision of spike timing was found to depend on stimulus transients. Constant stimuli led to imprecise spike trains, whereas stimuli with fluctuations resembling synaptic activity produced spike trains with timing reproducible to less than 1 millisecond. These data suggest a low intrinsic noise level in spike generation, which could allow cortical neurons to accurately transform synaptic input into spike sequences, supporting a possible role for spike timing in the processing of cortical information by the neocortex.

Response variability in retinal ganglion cells of primates

The signal encoded by a sensory neuron is usually characterized as the cell's average response to repeated presentations of a stimulus. However, each stimulus presentation elicits a slightly different response. This response variability may obscure the signal represented by neural activity, but it might also be an important aspect of a neuron's message and in some instances may even serve useful function. Here we present evidence that response variability (noise) in primate retinal ganglion cells at photopic light levels is (i) independent of the amplitude of either the stimulus or the response and is therefore additive, (ii) independent of receptive field size and retinal eccentricity, and (iii) similar for all primate ganglion cells. Our results show that the primate retina maintains a uniform noise level across the entire visual field and suggest that the noise originates within the ganglion cells themselves.

Effects of serotonergic agonists and antagonists on ganglion cells in the goldfish retina

Extracellular recordings were made from the isolated goldfish retina during superfusion with various serotonergic agonists and antagonists to determine the effects of these drugs on the maintained activity and response properties of the ganglion cells. Superfusion of the retina with serotonin (25-500 microM) increased the maintained activity of OFF-center ganglion cells and decreased the maintained activity of ON-center ganglion cells. In addition, serotonin also attenuated the excitatory responses to annular stimuli, suggesting a decrease in the strength of surround input to the ganglion cells. The effects of serotonin on OFF-center ganglion cells were mimicked by the nonselective 5-HT1 agonist 5-MeOT and the 5-HT1A receptor agonist 8-OH-DPAT, while only 5-MeOT mimicked the action of serotonin on ON-center ganglion cells. The effects of exogenously applied serotonin on the ganglion cells could be blocked by the mixed 5-HT1/5-HT2 receptor antagonist methysergide but not by the 5-HT2 receptor antagonist mianserin or the dopamine receptor antagonist haloperidol. These results support previous anatomical and biochemical evidence that serotonin functions in a neurotransmitter or neuromodulatory role in the teleost retina and suggest that serotonin may be involved in modulating the maintained activity and surround input to the ganglion cells. The results also indicate that two different types of receptors may mediate the actions of serotonin in the ON and OFF pathways, respectively.