Huge new dataset pushes limits of neuroscience

Most introductory neuroscience courses show a video. It doesn't look like much, a bar of light rotating across a black screen while the background audio pops and crackles like the sound of a fireworks show The pops represent the firing of a single neuron in the brain of a cat who is watching a bar move. The popping occurs when the bar reaches a specific location and lies at a certain angle. This neuron really cares about that bar.

The basic principles of how the visual system works were deduced from an experiment performed in the 1960's by David Hubel and TorstenWiesel. For decades, neuroscientists have stuck thin, metal electrodes into the brains of mice, finches, and monkeys to figure out what makes them tick. Specific colors, shapes, or locations in space or the direction of one's head are just some of the things that the brain responds to.

As powerful an engine as single-cell analysis has proven, “Everybody always wanted more neurons,” says Anne Churchland, professor of neurobiology at the University of California, Los Angeles. Part of the reason was simple statistics: More observations are always better, no matter the experiment. But scientists also ran up against analytical walls when they looked at neurons one-by-one. In the prefrontal cortex, the region at the front of the brain that plays major roles in planning, decision-making, and social behavior, neurons respond to such a diversity of things—visual features, tasks, decisions—that researchers have been unable to assign them any particular role, at least individually. Even in the primary visual cortex, the area far to the back of the brain where Hubel and Wiesel made their recordings, only a fraction of neurons actually fire when the animal looks at oriented bars. Advertisement

It was not possible to look at more than a few of the same cells at the same time. Engineers have pushed and pushed that capacity, which culminated in the development of neuroscience probes. One centimeter long and made of Silicon, a single probe can listen to hundreds of neurons at the same time and is small enough that it can be stuck into an animal's brain. The Allen Institute used six probes to record from different parts of the mouse's visual system at the same time. In August the institute released data from 81 mice. Any researcher who wants to use the data is free to do so.

The release lets researchers observe enormous groups of neurons acting in concert, three times as big as the previous record holder. The scientific community has not been able to understand parts of the brain that are related to cognitive functions. Shawn Olsen is an investigator at the Allen Institute who played a central role in the project. It doesn't happen at the level of single brain cells.

The challenge is figuring out how to make sense of it all. Sharing anddownloading Gargantuan data sets can be hard. Working with such data sets allows researchers to study the brain on its own terms.

The brain looked like an assembly line of groups of cells, each specialized for a specific purpose. If you show someone a red balloon, they'll respond with their own signals. The brain is so densely wired up that no single cell is ever acting alone. Fusi says that the brain doesn't look at a single neuron at a time. They are looking at a lot of other cells. We should look at it the same way.