Duke University researchers managed to take a giant step forward when their experiment, focused on observing exactly how vision develops in simple brains, succeeded. The team observed the changes a ferret's brain underwent after it first opened its eyes, 30 days from its birth. The way in which neurons arranged themselves, so as to be able to interpret moving images, was observed using multiple sophisticated lab techniques.
The scientists used a process called "in vivo two-photon laser scanning microscopy," which allowed them to observe the calcium levels neurons were giving off when the animal opened its eyes. These spikes in calcium levels are usually associated with electrical impulses being passed between neurons, just before they come together to form cortical columns. These are areas that are occupied by neurons having the same "preference" on the signal they analyze.
For example, vertical motion tracking has its own such columns, while horizontal tracking is processed by different columns. The mechanism by which the brain decides which way the object it sees is going is rather complex. All neurons in the visual cortex participate, and each gives its own "opinion," via electrical signals. Those brain cells that were pre-programmed to form specific cortical columns give the strongest signal and the brain chooses to listen to them over the others.
The scientists say that, when the ferret is born, its eyes remain closed until the end of the first month of life. They discovered that, before that time, the brain cells that are to form columns and process video signals are not yet formed. This led them to conclude that earlier brain cells are not yet fully formed, but rather exist chaotically and undifferentiated.
"Many people don't realize that the vast majority of cortical connections are being formed at a time when experience can influence neural activity. Understanding how experience shapes the architecture of developing neural circuits, and identifying the underlying cellular and molecular mechanisms could provide the key to a number of developmental brain disorders," concluded neurobiology professor David Fitzpatrick, who is also the director of the Duke Institute for Brain Sciences.
