May 28, 2013
Rat’s Move Their Eyes In Opposite Directions When Running For Unique View
Lee Rannals for redOrbit.com — Your Universe Online
Max Planck Institute (MPG) scientists have found that rats move their eyes in opposite directions in both the horizontal and the vertical plane when running. This gives the rats a unique perspective on the world around them.
The team discovered that each rat eye moves in a different direction, depending on the change in the animals' head position. They analyzed both eyes and found that one of the eye movements exclude the possibility that rats fuse the visual information into a single image, but instead move in a way that enables the space above them to be permanently in view. This unique adaptation helps them deal with the major threat from predatory birds that rodents face in their natural environment.
A rat's eye position enables it to have a very wide visual field, but making it tougher to acquire three-dimensional vision. The visual system of these animals needs to meet two conflicting demands at the same time, including maximum surveillance and detailed binocular vision. The Max Planck Institute researchers observed and characterized the eye movements of freely moving rats to get a better understanding of this vision system.
The team fitted minuscule cameras weighing only about one gram to the animals' heads, which could record the lightning-fast eye movements with great precision. The scientists also measured the position and direction of the head to help them reconstruct the rats' exact line of view at any given time.
The scientists found that although rats process visual information from their eyes through very similar brain pathways to that of other mammals, their eyes move in a totally different way.
“Humans move their eyes in a very stereotypical way for both counteracting head movements and searching around. Both our eyes move together and always follow the same object. In rats, on the other hand, the eyes generally move in opposite directions,” Jason Kerr, from the Max Planck Institute for Biological Cybernetics, explained in a statement.
Kerr and his colleagues also discovered that the eye movements largely depend on the position of the animal's head.
“When the head points downward, the eyes move back, away from the tip of the nose. When the rat lifts its head, the eyes look forward: cross-eyed, so to speak. If the animal puts its head on one side, the eye on the lower side moves up and the other eye moves down.” Kerr added.
Human eyes must move in the same direction in order to properly see. If there is a deviation measuring less than a single degree in the human eye, it causes double vision. In rats, the opposing eye can vary by as much as 40 degrees in the horizontal plane and up to 60 degrees in the vertical plane.
A rat's unusual eye movements could have evolved to adapt to the animals' living conditions. The scientists believe that permanent visibility in the direction of potential airborne attackers increases the animals' chances of survival.
Another unique trait rats have is their ability to communicate through sniffing.
Scientists from Case Reserve University School of Medicine found that when two rats approach each other, dominance is communicated by more frequent sniffing. The subordinate rat signals its role by sniffing less in the interaction. They said if the subordinate rat sniffed more than it was supposed to, it would evoke an aggressive response.