The Danger of Boundaries in the Brain

Categorizing brain regions has drawbacks, argues neuroscientist Mark Humphries in a new blog post. One of the goals of the Simons Collaboration on the Global Brain is to transcend artificial boundaries by recording from many neurons across the brain.

Alyssa Picchini Schaffer is the SCGB’s scientific officer.

Humans like to name and categorize things. It helps us communicate, organize and make sense of our world. But the labeling process has also been long fraught with disagreement — scientists can rarely agree on the features that are most important for categorizing biological entities. For example, even before he published the Origin of the Species, Charles Darwin outlined the lumper-splitter problem: Splitters create ever-smaller and more specific categories, whereas lumpers make large groupings and assume that similarities within the categories are more important than differences.

The most important question for me, however, is not how best to define a category. Rather, do these categories help us or hinder us from understanding the underlying biology?

In a blog published in January, aptly titled “Evolution Doesn’t Give a Damn What You Think a Brain Region Is Called,” neuroscientist Mark Humphries of the University of Manchester expertly lays out the argument that categorization and naming is a human construct that can be useful in some ways but does not necessarily constrain biology. More specifically, it does not constrain brain function.

By naming these bits of brain, we can communicate effectively, we can talk about brains and know we are talking about the same bit…. But it is also a dangerous game. If we confuse the convenience of naming with the reality of the brain, we end up in deep trouble. Because evolution does not give a crap what we call a brain region.

Giving small chunks of brain tissue different names does not make them functionally distinct regions. Humphries offers the example of the primary motor and somatosensory cortices, which physically sit next to each other but are generally treated independently. “They appear in different chapters in textbooks. Entirely separate fields of research have grown up around them,” he writes.

But as Humphries points out, barring “border guards who turn away the motor cortex neuron axons at the crossing with somatosensory cortex, and the same from the other direction,” these two regions are almost certainly more intimately intertwined than we give them credit for. “A small set of neurons in somatosensory cortex get direct sensory input, and a small set of neurons in motor cortex connect to the spinal cord. Most of the neurons in these bits of cortex neither get sensory input from the thalamus nor project to the spinal cord. They are wired to other neurons all over cortex, and very much to each other,” Humphries writes.

By ignoring that fact, we may miss something important about brain function.

The Simons Collaboration on the Global Brain aims to transcend artificial boundaries in the brain by focusing on large-scale recording at single-cell resolution. This approach allows us to readily investigate brain activity across named brain areas. By combining proper theory and analysis to decipher the large-scale activity, we’re more likely to uncover how wide-ranging neural circuits — those that traverse traditionally defined borders — help the brain execute its essential functions.

Naming brain regions serves an obvious purpose. But it is time to stop seeking labels as ground truth and search for the underlying principles of brain function.

Alyssa Picchini Schaffer is the SCGB’s scientific officer.