Spying on the Brain

Researchers use MRI to track dopamine and map neural activity.

Launched in 2013, the national BRAIN Initiative aims to revolutionize our understanding of cognition by mapping the activity of every neuron in the human brain, revealing how brain circuits interact to create memories, encode new skills, and interpret the world around us.

Before that can happen, neuroscientists need new tools that will let them probe the brain more deeply and in greater detail, says Alan Jasanoff, an associate professor of biological engineering. “There’s a general recognition that in order to understand the brain’s processes in comprehensive detail, we need ways to monitor neural function deep in the brain with spatial, temporal, and functional precision,” he says.

Jasanoff and colleagues have now taken a step toward that goal: they have developed a technique that allows them to track neural communication in the brain over time, using magnetic resonance imaging (MRI) along with a specialized molecular sensor. This is the first time anyone has been able to map neural signals with high precision over large brain regions in living animals, offering a new window on brain function, says Jasanoff, who is also an associate member of MIT’s McGovern Institute for Brain Research.

His team used this molecular imaging approach, described recently in Science, to study the neurotransmitter dopamine in a region called the ventral striatum, which is involved in motivation, reward, and reinforcement of behavior. This region combines dopamine signals with sensory information from other parts of the brain to reinforce behavior and help the brain learn new tasks and motor functions, and it also plays a major role in addiction.

The researchers tracked dopamine—one of many neurotransmitters that help neurons communicate with each other over short distances—using an MRI sensor consisting of an iron-containing protein that acts as a weak magnet. When the sensor binds to dopamine, its magnetic interactions with the surrounding tissue weaken, dimming the tissue’s MRI signal.

With this sensor, Jasanoff’s team was able to precisely measure dopamine concentrations in the ventral striatum after electrical stimulation of the mesolimbic pathway—an important source of dopamine in the brain.

Jasanoff now plans to use this sensor to study the brain regions most affected by Parkinson’s disease, which is caused by the death of dopamine-generating cells. His lab is also working on sensors to track other neurotransmitters to make it possible for researchers to study how they interact during different tasks.

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