Extending our maps of the brain

January 20, 2017

Even well-charted territory in the brain can contain surprises. Researchers at the Allen Institute for Brain Science have recently published data in the journal eLife that raise interesting questions about how we draw borders between regions in the visual part of the brain.

Visual information is relayed and processed through the part of the surface of the brain called the visual cortex, which is composed of a series of interconnected sub-areas. One way to map these areas is to look at physical markers in the brain. Changes in cell density, myelination or the concentration of certain chemicals can mark where one area ends and another begins. Another more functional approach looks at how cells respond to visual information, using that data to see how the brain creates topographic maps of the outside world. The area maps generated by these two methods are generally thought to align with each other.

Allen Institute scientists looked into how closely these maps actually align by creating both types of maps in the same mice. Using a fluorescent protein called GCaMP6, they measured how sub-regions of the visual cortex responded to visual cues, and then later, measured the anatomic borders in the same brains.

Comparing the two types of maps showed that the areas do not always align, and that the visual part of the mouse brain may more closely resemble the primate brain than previously thought.

“Activity-based organization seems more extensive in mouse cortex than previously appreciated,” says Jun Zhuang, Ph.D., Scientist II at the Allen Institute for Brain Science and first author on the paper. “Looking at the functional data, we see areas that resemble secondary visual processing in a fairly similar pattern to primates, and in a way that does not quite align with the structural borders often identified in the mouse visual cortex.”

“Despite the fact that these two types of maps don’t seem to align, these findings actually bring some clarity to the field,” says Jack Waters, Ph.D., Associate Investigator and senior author on the paper. “The location of higher order processing in the mouse brain, such as unifying a vertical line and horizontal line to identify a corner, has eluded the field for some time. The functional data we collected point to where that kind of processing could be taking place.”