Stimulus discrimination via responses of retinal ganglion cells and dopamine-dependent modulation.

Neighboring retinal ganglion cells (RGCs) fire with a high degree of correlation. It has been increasingly realized that visual perception of the environment relies on neuronal population activity to encode and transmit the information contained in stimuli. Understanding how neuronal population activity contributes to visual information processing is essential for understanding the mechanisms of visual coding. Here we simultaneously recorded spike discharges from groups of RGCs in bullfrog retina in response to visual patterns (checkerboard, horizontal grating, and full-field illumination) using a multi-electrode array system. To determine the role of synchronous activity mediated by gap junctions, we measured the correct classification rates of single cells' firing patterns as well as the synchronization patterns of multiple neurons. We found that, under normal conditions, RGC population activity exhibited distinct response features with exposure to different stimulus patterns and had a higher rate of correct stimulus discrimination than the activity of single cells. Dopamine (1 μmol/L) application did not significantly change the performance of single neuron activity, but enhanced the synchronization of the RGC population activity and decreased the rate of correct stimulus pattern discrimination. These findings suggest that the synchronous activity of RGCs plays an important role in the information coding of different types of visual patterns, and a dopamine-induced increase in synchronous activity weakens the population performance in pattern discrimination, indicating the potential role of the dopaminergic pathway in modulating the population coding process.