Late last week, we started seeing headlines about how new research suggested we might have two brains instead of the one that seems to show up on MRIs. As is often the case, these rumors can be traced back to a single press release issued by one of the universities where the work was done.
You don’t have two brains. It’s a silly way to look at the results of the new article.
But there are much better ways to look at the results, ways that can help us understand how the brain is built and illustrate some of the general ideas behind developmental biology. So let’s take a look at what the research actually shows and put it in the context of brain development.
Where are you?
You might think of body segments as something that appears in things like crustaceans and insects. But our nervous system also develops in segments. Vertebrates have four main ones: the forebrain, the midbrain, the hindbrain and the spinal cord. (Some of these develop segments within them, but we’ll skip those.) The new article focuses largely on providing part of the answer to an obvious question: how do those segments get there?
Those kinds of questions are the bread and butter of developmental biology, a field that focuses on how organisms start as a single cell and, through a series of carefully timed and choreographed processes, produce all the tissues found in adults.
To think about the question, we need a little context. When the first cells committed to becoming neurons appear, the vertebrate embryo already distinguishes the head from the tail and the back from the belly. (We won’t go into how the embryo learns that, but we know a lot about that too.) The embryo consists of three tissues at this time: the endoderm, which will line our intestines, the mesoderm, which will form muscles and bones, and the ectoderm, which will form the skin.
