With new technology comes the opportunity to explore biology from new angles, measure with yet-unseen accuracy and visualize at much broader or tinier scales than ever before. New functional magnetic resonance imaging technology is no exception, and both hardware, such as ultrahigh magnetic fields, and software, such as new technologies for image collection, have been rapidly pushing the frontiers of clinical and research applications.

Most recently, Beckman researchers used 7 Tesla fMRI technology to map out decision-related brain processes that operate on too small a scale to be seen with conventional, lower magnetic field imaging.

“In conventional human brain imaging, the typical resolution is 2-to-3 millimeters, so you cannot resolve the functions of very small structures,” said Yuhui Chai, 7T research scientist at Beckman’s Biomedical Imaging Center. “But ultra-high field MRI allows us to have high, submillimeter resolution, so we can resolve the function in small structures which could not be resolved before.”

The University of Illinois Urbana-Champaign and Carle Health co-own and co-operate a 7 Tesla MRI scanner, used for both research and clinical tasks, through the Carle Illinois Advanced Imaging Center. The ‘7 Tesla’ designation indicates the strength of the scanner’s magnetic field. This greater-strength field allows researchers and clinicians to take much more detailed images compared to those taken by conventional 3 Tesla scanners.

Specifically, Chai and Brad Sutton, director of the Biomedical Imaging Center, used 7T fMRI to understand what happens in our brains when we make decisions. They teamed up with Joshua Goh, a previous post-doctoral researcher at the Beckman Institute and a current associate professor at National Taiwan University.

“This project is an excellent example of how we can advance our understanding of the brain through multidisciplinary collaborations, bringing together advanced imaging systems with tailored acquisitions from Dr. Chai and a precise cognitive task from Dr. Goh,” Sutton said. “This unlocks key insights into detailed pathways in the brain.”

Decision-making is a complex, crucial process. Far from a single action, decision-making can be broken down into smaller steps – for example, assessing a situation, selecting a choice and learning from the results. Many regions of the brain work in tandem to execute these steps. Researchers know what many of these regions are, but until now, some of their specifics have gone unexplored because they operate on such a small scale.

For this study, the researchers developed a task similar to gambling in which participants were asked to accumulate as many points as they could by accepting or rejecting lottery stakes. For example, a participant might be presented with the opportunity to win 40 points, and would also be informed that they had a 70% chance of winning.

Crucially, the task included superhigh stake trials: high-risk, high-reward situations in which participants had less time to make their decision. These trials were present because they caused stronger, more detectable responses in the brain compared to the responses associated with normal trials.

Overall, these methods let the researchers map out the regions responsible for different steps in the decision-making process and how these regions interact with each other. 

One region of particular interest was the locus coeruleus, a tiny site in the brainstem that is only a few millimeters across. With conventional imaging, which typically has a resolution of 2-3 millimeters, it is difficult to distinguish such a small structure from its surroundings and effectively resolve its functional responses. However, 7T fMRI can effectively distinguish the locus coeruleus and image these responses.

The researchers found that at the very beginning of decision-making, the locus coeruleus determines how much of the brain’s processing power should be allocated to making a choice. This is a very important task – if too few or too many resources are allocated, relevant information may not be processed correctly. 

“The locus coeruleus is a very tiny region – it’s about 2 millimeters wide – but it’s extremely important for modulating the whole brain so the brain can focus on the task that the subject wants to focus on,” Chai explained. “The locus coeruleus responds very strongly to situations with super-high stakes.”

Another region that the study focused on was the gray-matter bridge, which is a 1 millimeter wide connection between two brain regions: one which evaluates a decision, and another which is responsible for choosing the next steps. Its role in humans has been mostly unexplored until now, but this study suggests that it facilitates making rapid choices.

The researchers also zoomed in on the prefrontal cortex: a region at the very front of the brain which is well-known for its importance in decision making. Less well studied are the specific roles of the stacked layers, together about 3 mm thick, that make up the cortex. With the 7T MRI, the research team could examine activity across different cortical layers, and found that they showed different responses at different stages of decision-making. In other words, different processes happen across different cortical layers.

The team plans to expand upon this research in the coming future.

“This study was done in healthy, younger adults, and our plan is to extend it to different age groups because a lot of mesoscale structures resolved in this study are very related to aging, development, and neurodegenerative diseases like Alzheimer's,” Chai said.

The paper, “Resolving mesoscale brainstem-prefrontal-striatal pathways underlying decisions upon salient events using submillimeter-resolution fMRI”, is available here.

This work was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award R03EB034324.