Primate Eye Functions Like a Digital Camera

The eyes of all primates function like a digital camera and process visual information using small computing units located in the visual cortex of their brains, according to scientists at University of Geneva. A study was done to understand the origins of our visual abilities and published in the journal Current Biology, in which the scientists compared the visual system of the mouse lemur to that of other primates and found that the size of these visual processing units is identical in all primates, independent of their body size. As the mouse lemur is a very special species, sharing many traits with the very first primates that evolved 55 Million years ago, these results suggest an incredible preservation of our visual system and highlight the importance of vision in our daily lives and that of our ancestors in the distant past.

The visual system of the mouse lemur was studied using an optical brain imaging technique. Geometrical shapes representing lines of various orientations were presented to the lemurs and the activity of the neurons responding to the visual stimuli was imaged. The repetition of such measurements gradually allowed them to determine the size of the minimal processing unit. “We expected to see a unit of tiny size, proportional to the small size of the mouse lemur, but our data revealed that they measure more than half a millimeter in diameter,” says Daniel Huber, Professor in Department of Basic Neurosciences.

In collaboration with the Max Planck Researchers, Huber compared hundreds of these units imaged in the tiny mouse lemur brain with the data obtained for the visual circuits of other, much larger primate species. The team made a surprising discovery: not only was the basic processing unit almost identical in size in the 60-gram mouse lemur, as in larger monkeys such as macaques weighing about seven kilograms, or even larger primates such as us humans.

They also found that the way the units are arranged across the brain was totally indistinguishable, following the same rules with mathematical precision. The researchers also found that the number of nerve cells per visual unit was almost identical in all primates studied so far.

According to Daniel Huber,the study also highlight the crucial importance of conserving the habitat of primate species such as the mouse lemur, particularly in the forests of Madagascar. These habitats are disappearing at an alarming pace, taking with them precious keys to understanding our own origins.