Researchers at the Salk Institute for Biological Studies have discovered a neural circuit that is likely to play an important role in the visual perception of moving objects. Their finding, published in the April issue of the journal Neuron, forces neurobiologists to rethink the neural pathways that our brain relies on to detect motion.
It had long been assumed that sensory information about color and fine detail is relatively unimportant for the perception of moving objects. Mainly, because the neural pathways in the brain carrying color and fine detail information seemed to be completely separate from areas of the brain previously associated with motion processing.
In an elegant anatomical study, Salk researchers now show that a neural pathway carrying color and fine detail does connect to the motion processing areas of the cortex (the outer layer of the brain), and this information most likely helps the brain detect moving objects.
"There are many different kinds of cues in the visual environment that can be used to detect motion - basically anything that is moving," says Edward M. Callaway, Ph.D., senior author of the study and a professor in the Systems Neurobiology Laboratory. "We asked the question, 'Is motion processing taking advantage of the full range of possible cues?' "
This study demonstrates, for the first time, that it is.
Our eyes take in the visual environment and break the incoming images down into three main components: color, position, and brightness. These pieces of information are channeled from the eye to the brain along separate, specialized pathways. The parvocellular (P) pathway carries information about color and fine spatial detail. The magnocellular (M) pathway, on the other hand, is colorblind and has poor spatial resolution; instead, it is sensitive to low contrast and rapid changes. The visual cortex uses the information from these pathways to compute further details about motion, shape, and color.
Until now, it was thought that only the M pathway connected to the cortical motion processing area called MT. This is because the M and P pathways remain separate as they extend through the brain to the primary visual cortex (V1). And the cells in V1 that provide input to MT appeared to receive input from only the M pathway. The new results show that these cells also receive input from the P pathway.