Measuring energy expended by nerve cells, Yale team finds it’s all in a day’s work

For the first time, a team of Yale scientists has quantified the link between the work neurons perform for sensory or cognitive tasks and the energy they expend.

“These results could later contribute to more targeted treatments for certain brain disorders, where brain imaging is involved,” said Fahmeed Hyder, Ph.D., assistant professor of diagnostic radiology.

The team’s work could also change approaches to the use of data from functional magnetic resonance imaging (fMRI). It has been common practice for neuroscientists to take fMRI images from a baseline phase and compare them to images obtained during the performance of the task. The result is a difference map which shows where tasks have led to increased brain activity.

“If all they look at are these differences from baseline, then they’re ignoring an important fraction of the total work required for brain function and perception,” Hyder said. “Not everyone starts at the same baseline. Even in our animal experiments, which were done under very well-controlled conditions, there are still slight variations in the baseline, and incremental changes from baseline alone can’t accurately reflect the amount of energy used. Only the total energy used can reflect the total activity within a region.”

Hyder and his colleagues measured the firing of neurons in the brains of rats as the neurons sent electrical signals from one region to another. Then they varied the workload for neurons in a specific brain region. By using fMRI to measure local energy use, they were able to estimate the energy the neurons expend when the workloads are varied.