Data compression in the brain: When the primary visual cortex processes sequences of complete images and images with missing elements --- here vertical
Researchers have assumed that visual information in the brain was transmitted almost in its entirety from its entry point, the primary visual cortex (V1). “We intuitively assume that our visual system generates a continuous stream of images, just like a video camera,” said Dr. Dirk Jancke from the Institute for Neural Computation at Ruhr University.
“However, we have now demonstrated that the visual cortex suppresses redundant information and saves energy by frequently forwarding image differences,” similar to methods used for video data compression in communication technology.
Using recordings in cat visual cortex, Jancke and associates recorded the neurons’ responses to natural image sequences such as vegetation, landscapes, and buildings. They created two versions of the images: a complete one, and one in which they had systematically removed vertical or horizontal contours.
If these individual images were presented at 33Hz (30 milliseconds per image), the neurons represented complete image information. But at 10Hz (100 milliseconds), the neurons represented only those elements that were new or missing, that is, image differences.
To monitor the dynamics of neuronal activities in the brain in the millisecond range, the scientists used voltage-dependent dyes. Those substances fluoresce when neurons receive electrical impulses and become active, measured across a surface of several square millimeters. The result is a temporally and spatially precise record of transmission processes within the neuronal network.