Keynote Series: Seong-Gi Kim — Feedforward or feedback: Measuring directionality of information flow with ultrahigh field fMRI

By Alexander Albury

The advancement of functional magnetic resonance imaging (fMRI) has made it increasingly easier to observe what happens in the brain in real time. However, the temporal resolution of fMRI is often limited by the hemodynamic response, the rate at which blood flows to and from tissues in the brain. This can make it hard for neuroscientists to observe rapid changes in brain activity using fMRI in the same way they might using tools like electroencephalography (EEG) and magnetoencephalography (MEG) which measure faster physiological processes. But as MRI technology improves, fMRI measurements are becoming more precise, allowing researchers greater specificity when studying smaller changes in brain activity.

A group of researchers led by Seong-Gi Kim at Sungkyunkwan University took advantage of ultra-high-field MRI to test how feasible it was to measure the direction of information flow across brain regions. They employed a clever design to measure the transmission of information across neural circuits by stimulating them at different “ends” of the circuit. 

Information flow in neuroscience is commonly grouped into two categories; top-down processes and bottom-up processes. Bottom-up refers to stimulation coming from outside the system, for example, touching your hand to a hot stove. This information has to travel from the receptors in your fingers along the nerves leading to your brain before your brain can trigger a muscle response that makes you move your hand away. Top-down processes are those that rely on previous experiences and knowledge, for example, solving a puzzle based on your knowledge about how it should look. While thoughts and behaviors typically require a diverse combination of both top-down and bottom-up processing, these are still helpful frameworks to examine information flow in the brain.

The researchers led by Dr. Kim examined neural information flow in mice brains using two types of stimulation conditions. In the first condition, they stimulated the front paw of the mouse using short electrical pulses. In the other condition, they used optogenetics to directly stimulate neurons in the motor cortex of the mouse. They then used high-resolution fMRI to measure the transmission of this stimulation through the brain. The researchers found the opposite pattern for each of the stimulus types. Activity from the paw stimulation originated in lower sensory regions and progressed to higher regions in the motor cortex. Whereas optogenetic stimulation in the motor cortex progressed from cortical regions to subcortical regions.

These findings demonstrate the ability to use ultrahigh field MRI to measure the direction of information flow in the brain over very short timescales. As more powerful MRI scanners become available for use with humans, the imaging techniques used by these researchers can be applied to more accurately monitor brain activity in human subjects.

Original Research:

Jung, W. B., Im, G. H., Jiang, H., & Kim, S.-G. (2021). Early fMRI responses to somatosensory and optogenetic stimulation reflect neural information flow. Proceedings of the National Academy of Sciences, 118(11), e2023265118. https://doi.org/10.1073/pnas.2023265118

If you’d like to know more about Dr. Kim’s research, check out our interview with him here.