MT, which is located a couple of inches behind and above the ear, specializes in the perception of complex motions and is a distinctive feature in the brains of primates. Neuroscientists have found this special feature in the brains of all the primates that they have searched for it, including humans. However, it is a feature that our closest evolutionary cousins, tree shrews and rodents, lack. (Curiously, cats appear to have developed a similar visual center independently.)

Now a study, published in the Proceedings of the National Academy of Sciences, provides new support for the hypothesis that MT evolved early in the course of primate evolution when our small, long-nosed, bewhiskered and hyperactive ancestors were breaking out of the understory role that they had occupied during the age of the dinosaurs to claim niches that were abandoned as the "thunder lizards" died out.

Using a technique called "in vivo optical imaging," a team of researchers from Vanderbilt University performed the first detailed analysis of the MT center of a prosimian, a family that diverged from the line of human evolution more than 60 million years ago. The subject of the study was a small nocturnal primate with large eyes called the galago, or bush baby. They found that the bush baby's MT region is organized in a way that is strikingly similar to that of monkeys. The finding provides new support for the argument that this specialized visual center evolved in a common ancestor of prosimians and humans. It also makes it more likely that the human MT is organized in similar fashion.

"The idea is that when a given characteristic is shared between distantly related primates, it is highly likely that it came from a distant ancestor," says team leader Vivien Casagrande, professor of cell and developmental biolog
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Contact: David F. Salisbury
david.salisbury@vanderbilt.edu
615-343-6803
Vanderbilt University
15-Apr-2004