Ashley Antony

Yale scientists are now one step closer to understanding the complexities of the brain.

Neuroscience researchers at the Yale School of Medicine have identified a way to simultaneously measure the activity of a single neuron and the activity between brain regions in mice. This new method may provide new insights into the links between cells, circuits and behavior, the researchers told the News. The study was published in Nature Methods on Nov. 4.

“By creating a method where we could do two levels of analysis simultaneously — a cellular resolution view and a whole-cortex view — we are trying to help bridge the gaps,” said Daniel Barson MED ’22 GRD ’22, who is the first author of the study.

A major challenge for neuroscientists is piecing together cellular and regionwide data, according to Barson. For example, data collected separately using an FMRI — which measures blood flow throughout the brain — will produce a different sense of brain activity than electrophysiology that measures impulses generated by single neurons.

Xilin Shen, a co-author and associate research scientist at Yale, said she developed the algorithm to identify coactivation between individual neurons and whole-brain dynamics — making it possible for the new method to analyze several hundred individual neurons
with higher resolution while simultaneously recording data from other areas of the brain.

“For the first time we can combine both of these modalities simultaneously and see how individual genetically defined neurons are activated across the entire cortical surface. This is the main highlight of the paper,” said Ali Saddam Hamodi, co-author of the study and a postdoctoral fellow at the School of Medicine.

The method combines two microscopy techniques. The first, called two-photon imaging, is used to analyze brain tissue measuring several hundred microns wide. The technique uses a high-powered laser that sends individual packets of light into the brain to excite green fluorescent protein, or GFP. Two-photon imaging, Barson explained, is able to precisely measure neuron activity deep within brain tissue by using infrared light. Similar to how shining a flashlight through your finger causes a red appearance, infrared light can penetrate tissue even deeper — eliciting a visual cue from the green fluorescent protein that scientists measure.

The second technique, called widefield imaging, involves shining blue light to the brain. The measurable response from GFP is less specific and originates from neurons closer to the brain’s surface.

“Each of these modalities by themselves are very powerful, but they each have limitations,” Hamodi said. “Photon imaging is from a small point of view, so you don’t have an idea what is happening across the entire cortical mantel — like how different neurons are activated. Widefield imaging allows you to see large-scale activity but you don’t have the resolution, how many cells are active at any given event or where the signal is coming from exactly.”

Using both two-photon and widefield imaging techniques, scientists have now developed a new way to analyze the brain. According to Barson, the ultimate goal of this project is to build a model of how different neurons contribute to brain activity based on data collected through the new method.

“This two-photon imaging is pretty commonly used in neuroscience to report from a few hundred neurons,” Barson said. “We combined the method of two-photon imaging with widefield imaging to get a sense of the entire brain, all at once.”

Green fluorescent protein was first observed in 1962.

Tamar Geller | tamar.geller@yale.edu