Researchers at the University of Pennsylvania School of Medicine estimate that the human retina can transmit visual input at about the same rate as an Ethernet connection, one of the most common local area network systems used today. They present their findings in the July issue of Current Biology. This line of scientific questioning points to ways in which neural systems compare to artificial ones, and can ultimately inform the design of artificial visual systems. Two broad classes of ganglion cell types in the guinea pig retina: brisk cells, which are larger and transmit electrical impulses faster, and sluggish, which are smaller and slower
Much research on the basic science of vision asks what types of information the brain receives; this study instead asked how much. Using an intact retina from a guinea pig, the researchers recorded spikes of electrical impulses from ganglion cells using a miniature multi-electrode array. The investigators calculate that the human retina can transmit data at roughly 10 million bits per second. By comparison, an Ethernet can transmit information between computers at speeds of 10 to 100 million bits per second.
The retina is actually a piece of the brain that has grown into the eye and processes neural signals when it detects light. Ganglion cells carry information from the retina to the higher brain centers; other nerve cells within the retina perform the first stages of analysis of the visual world. The axons of the retinal ganglion cells, with the support of other types of cells, form the optic nerve and carry these signals to the brain.
Investigators have known for decades that there are 10 to 15 ganglion cell types in the retina that are adapted for picking up different movements and then work together to send a full picture to the brain. The study estimated the amount of information that is carried to the brain by seven of these ganglion cell types.
The guinea pig retina was placed in a dish and then presented with movies containing four types of biological motion, for example a salamander swimming in a tank to represent an object-motion stimulus. After recording electrical spikes on an array of electrodes, the researchers classified each cell into one of two broad classes: “brisk” or “sluggish,” so named because of their speed.