2015-05-23 01:34:13
It is as if it generates a photo pixel by pixel in your brain.
Sensory systems are essential for animals to survive in their environment and reproduce. In fact, adaptation to an advantageous environment for some animal species is only possible by modifying its sensory systems. This can lead either to a change in the importance that a certain sense acquires to the detriment of another, or, on the contrary, to the improvement of the sense for which the new environment demands greater effectiveness. For example, cats and lynxes see very well in low light conditions and, unlike bats, they have not developed an alternative sense to adapt to it, but rather have improved their night vision.
Although the capabilities of some vertebrates are surprising, they often pale when compared to the capabilities of insects, of which undoubtedly one of the best known is the cockroach. Apart from being one of the few species of arthropods that has a song dedicated to itself, these bugs have abilities that some superheroes or supervillains would like for themselves. Some species of cockroaches can hold their breath for more than 40 minutes, others can survive intense doses of radiation (hence it is said that cockroaches would survive after the nuclear holocaust), they can subsist on paper and glue, or live for weeks without head, which, today, is only within the reach of some political parties.
Cockroaches usually live in very dark places and, when threatened, escape into the darkness, which gives them an advantage only if they are able to detect low levels of light intensity with high efficiency. In fact, previous studies to the one I am going to report here had already determined that their ommatidia, that is, the simple eyes that form the compound eye of many insects, and also of cockroaches, are adapted to capture very low intensity of light.
However, the lower limit of light intensity that each cockroach ommatidia can detect to form an image remained unknown. Researchers from the University of Oulu, in Finland, undoubtedly one of the closest universities to the North Pole, address this interesting question and make a surprising discovery.
Before explaining what they discover and how they do it, I would like to pause for a moment to defend this type of research, which may seem cold and anodyne to many. Investigating how the cockroach’s nervous system detects light and manages it could be important, for example, to develop robots or night vision systems that help orientate themselves in the depths of a cave, or a mine, and facilitate beings very difficult human tasks. Therefore, studying how cockroaches see in near-darkness, in addition to its purely scientific interest, can have important technological repercussions.
Photo on photo
To find out the sensitivity of the cockroach’s visual system, scientists develop a virtual reality device without glasses (since, obviously, these insects cannot wear them easily, lacking ears). The system consists of placing the cockroach on a hollow ball of thin plastic, similar, although larger, to those that can be seen in some old devices similar to computer mice: trackbals. Placed on the ball, the cockroach can walk on it, making it spin. At a short distance around the ball, a hemispherical screen is placed, as if it were a curved movie screen, on which a pattern of light and dark bands that move across its surface is projected. This mobile pattern triggers a reflex response in the cockroach that causes it to start walking and head towards the bands. Obviously, the only thing the cockroach does is walk on the ball, staying in the same place (see video).
To find out the responses of the cockroach’s nervous system to light stimuli, the researchers implant an electrode in one of its ommatidia, which is capable of detecting the activity of photoreceptor cells when they are hit by photons. The scientists thus collect data on the activity of photoreceptor cells in different light conditions and do so in a total of thirty cockroaches, which they subject to the same procedure.
In light environments similar to those of a moonless night, researchers discover that each cockroach ommatidium absorbs a single photon every ten seconds, which is actually very little light. Despite this, cockroaches apparently see well and are able to detect the faint bands projected on the screen and move towards them.
The analysis of these data allows the researchers to conclude that the cockroach’s visual system stores the light information that it receives photon by photon to generate an image a posteriori, that is, an image composed of the small pieces of information that it is stored with each photon. It is as if it generates a photo pixel by pixel in your brain.
So, surprisingly, the cockroach has its own virtual reality device. These results, published in the Journal of Experimental Biology, reveal a new and extraordinary capacity of this repellent insect, which may make us hesitate before trying to crush it when we see it fleeing into the darkness.
Referencia: Cockroach optomotor responses below single photon level. Anna Honkanen et al., (2014). J Exp Biol 217, 4262-4268.
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