When we call someone "bird-brained," we might be right. New research indicates that the brains of birds, primates, and even some reptiles may have evolved from cells that started out the same.
In mammals, the outer layer of the brain—called the neocortex—is where most higher-order processing happens. When we move, use spatial reasoning, or speak, we're using our neocortex. In birds, a region of the brain known as the dorsal ventricular ridge, or DVR, is responsible for higher-order processing. But rather than being a thin layer on the brain's surface, it consists of clusters of cells called nodes. The avian DVR is so different from the mammalian neocortex that scientists figured that there was little relationship between them, if any.
Odd as it may seem, embryos of most vertebrate species start out looking similar. Birds, primates, reptiles--anything with a spine--all look alike in the early stages of development. Now, new research from the University of Chicago indicates that some of the cells in the neocortex and the DVR start out as the same kind of cell, growing in the same region of the embryonic brain. (This means that, before each of us was born, we had brain cells that could have grown up to belong to birds.) (Or, if you're Ray, maybe they actually did!)
In 2012, Dr. Clifton Ragsdale and his team of researchers at the University of Chicago discovered that certain genetic markers in brain cells of the mammalian neocortex matched with genes in the cells of several bird DVRs. A new study at Ragsdale's lab, led by graduate student Steven Briscoe, found that other neurons in the DVR share molecular signatures with a kind of communication cell in the neocortex called an IT neuron. These IT neurons help the neocortex communicate among its various layers and from one side of the brain to the other.
"The structure of the avian DVR looks nothing like the mammalian neocortex, and this has historically been a huge problem in comparative neuroscience," Briscoe explains. "Our identification of IT neurons in the bird DVR helps to explain how such different brain structures can give rise to similar behaviors."
Dr. Ragsdale sums up the study this way: "What this research shows is that [birds are] using the same cell types with the same kinds of connections we see in the neocortex, but with a very different kind of organization."
In fact, it suggests the possibility that birds and primates evolved intelligence independently, starting with the same cell types and developing different brain structures.
The original article includes data on alligators too! Want to read it? Find it here: "Neocortical association cell types in the forebrain of birds and alligators," Current Biology (2018).