Quantal encoding of information in a retinal ganglion cell.
A retinal ganglion cell receives information about a white-noise stimulus as a flickering pattern of glutamate quanta. The ganglion cell reencodes this information as brief bursts of one to six spikes separated by quiescent periods. When the stimulus is repeated, the number of spikes in a burst is highly reproducible (variance < mean) and spike timing is precise to within 10 ms, leading to an estimate that each spike encodes about 2 bits. To understand how the ganglion cell reencodes information, we studied the quantal patterns by repeating a white-noise stimulus and recording excitatory currents from a voltage-clamped, brisk-sustained ganglion cell. Quanta occurred in synchronous bursts of 3 to 65; the resulting postsynaptic currents summed to form excitatory postsynaptic currents (EPSCs). The number of quanta in an EPSC was only moderately reproducible (variance = mean), quantal timing was precise to within 14 ms, and each quantum encoded 0.1-0.4 bit. In conclusion, compared to a spike, a quantum has similar temporal precision, but is less reproducible and encodes less information. Summing multiple quanta into discrete EPSCs improves the reproducibility of the overall quantal pattern and contributes to the reproducibility of the spike train.
Freed
Michael A
MA
Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058, USA. michael@retina.anatomy.upenn.edu
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002452:Cell Count / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018698:Glutamic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D008959:Models, Neurological; D010775:Photic Stimulation / Q000379:methods; D016012:Poisson Distribution; D012165:Retinal Ganglion Cells / Q000502:physiology* / Q000528:radiation effects*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects
D018698:Glutamic Acid