Purple gentle imaginative and prescient of rodents

It is widely believed that rodents are functionally blind when their surroundings are illuminated with longer wavelength light that humans perceive as red. A new study published in eLife by Nader Nikbakht of the Massachusetts Institute of Technology and Mathew Diamond of SISSA – Scuola Internazionale Superiore di Studi Avanzati challenges this assumption and shows that rats are objects illuminated only by red light can distinguish exactly. “This result shows that rodents have very good visual shape perception even under conditions of weak activation of the retinal photoreceptors. The results have implications for the design of experiments and the housing of rodents, ”says Mathew Diamond, director of the SISSA Tactile Perception and Learning Lab.

Like many rodents, rats are largely crepuscular and can usually be found in poorly lit environments, even in daylight. Your retina is dominated by rods, with cones, the cells that lead to color perception and make up only 1% of the photoreceptors. “Rodents lack red cones, that is, the red light receptors. This could be one reason why scientists for many years thought that red light was perceived by rats as a complete lack of usable light, ”notes Nikbakht, who was a SISSA PhD student and postdoctoral fellow prior to joining MIT. He continues: “In fact, the inability to see red as a color does not necessarily mean that they cannot use long-wave lighting: we question the notion of form blindness under red light and, contrary to expectations, find good behavioral performance.”

Rats had to recognize the orientation of a solid disk-shaped object with parallel bars that were colored alternately white and black, thus forming a rectangular wave grid. Each experiment was carried out with light sources of different wavelengths and it was found that the animals performed well even at wavelengths that humans perceive as deep red. “Applications are immediate,” comments Diamond. “A complete understanding of the visual processing of these animals is important for the design and control of the behavioral and physiological experiments. For example, when a rat navigates an olfactory device under red light, it may be able to use both visual and olfactory cues. Another application is to ensure optimal ambient light conditions for the well-being of the animals in laboratory environments. It is common to keep the animals under dark red light at night, which is believed to be perceived as total darkness. Now we know that it is not dark for them ”.

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