New research has revealed that deep in the brain, in a structure called striatum, all possible movements that an animal can do are represented in a map of neural activity. If we think of neural activity as the coordinates of this map, then similar movements have similar coordinates, being represented closer in the map, while actions that are more different have more distant coordinates and are further away.

The study, led by researchers at Columbia University and the Champalimaud Centre for the Unknown, was published in the journal Neuron.

“From the ears to the toes and everything in between, every move the body makes is determined by a unique pattern of brain-cell activity, but until now, and using the map analogy, we only had some pieces of information, like single/isolated latitudes and longitudes but not an actual map. This study was like looking at this map for the first time.” said Rui Costa, DVM, PhD, a neuroscientist and a principal investigator at Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute and investigator at the Champalimaud Centre for the Unknown, in Lisbon. Dr. Costa and his lab performed much of this work while at Champalimaud, before completing the analysis at Columbia.

The brain’s striatum is a structure that has been implicated in many brain processes, most notably in learning and selecting which movements to do. For example, a concert pianist harnesses her striatum to learn and play that perfect concerto. Early studies argued that cells in the striatum sent out two simple types of signals through different pathways, either ‘go’ or ‘no go,’ and it was this combination of these two signals — acting like a gas pedal and a brake — that drove movement. However, Dr. Costa and his team argued that the reality is far more complex, and that both types of neurons contribute to movement in a very specific way.

“What matters is not how much activity there is in each pathway, but rather the precise patterns of activity,” said Dr. Costa. “In other words, which neurons are active at any particular time, and what sorts of movements, or behaviors, corresponded to that activity.”

The key to observing neural activity during natural behavior was that the mice had to be able to move freely and naturally. To accomplish this, the team attached miniature, mobile microscopes to the heads of the mice. This allowed them to capture the individual activity patterns of up to 300 neurons in the striatum. At the same time, each mouse was equipped with an accelerometer, like a miniature Fitbit, which recorded the mouse’s movements.

“We have recorded striatal neurons before, but here we have the advantage of imaging 200-300 neurons with single-cell resolution at the same time allowing for the study of population dynamics with great detail within a deep brain structure. Furthermore, here we genetically modified the mice so that neurons were visible when they were active, allowing us to measure specific neuronal populations. This gives us unprecedented access to the dynamics of a large population of neurons in a deep brain structure,” said Gabriela Martins, postdoctoral researcher and one of the leading authors.