Faster MRI scanures brain, activity in mice

The tweaking of a classic neuroscience method makes it track the brain activity of a mouse more efficiently than ever.

A modern twist of functional magnetic resonance (fMRI) provides an increase of multiple times in the sensitivity to time and allows it to reveal the intricate neural processes at the root of it. Researchers published their findings on October 13 in the journal Science 1.

 

A typical fMRI procedure measures brain activity indirectly by recording increases in blood flow in areas in which neurons are consumed more oxygen. The signal may be delayed by one second, which can reduce time sensitivity. The speedy cells require only milliseconds to transmit messages to each other.

Jang-Yeon Park, an MRI scientist working at Sungkyunkwan University in Suwon, South Korea, set out to improve the accuracy of fMRI’s temporal resolution to measure neural activity in the range of milliseconds. They did this by altering the software used by an intense MRI scanner to capture the data at every 5 millisecondseight times more than what the standard technique can record and by applying frequently repeated stimulation to the animals that they were studying. This reduced the slower-paced blood oxygenation signals, making it possible to monitor the brain activity that is faster-paced. Researchers named their method direct imaging of the neuronal activities or DIANA.

Quick change

In the research, an anesthetized mouse in an MRI scanner was given a slight electric shock to its face every 200 milliseconds. Between the shocks, the scanner recorded data from a small part of the brain of mouse every 5 milliseconds. It moved onto another area following the next shock. After the software had stitched everything together, the procedure produced a head-on view of one complete segment of the brain, which captured brain activity for a 200-millisecond duration. (Spatial resolution of 0.22 millimeters which is typical in high-intensity MRI.)

 

During the scan facial stimulation activated a portion of the brain that processes sensory inputs, which causes the brain region to be illuminated with signals. The team discovered that this “DIANA response” was occurring simultaneously neurons released signals, or spiked which was assessed separately with a surgically-inserted probe. Additionally, researchers were in a position to track the DIANA signal’s path through the brain’s circuit in which groups of neurons sequentially stimulated each other.

 

It’s not evident what triggers DIANA. It isn’t entirely clear what triggers the DIANA response, but. When neurons transmit messages they expand, and the water molecules around them get altered. The water changes could be detected as signals (MRI machines typically detect signals generated by hydrogen atoms within the water molecules). Further studies showed that the DIANA response was associated with the length of time that it takes for ions to flow into neurons, which alters their voltage, leading them to spike and transmit messages. Park and his team suggest it is possible that the DIANA signal is caused by several neurons altering their voltage.

 

More details to follow

While the team hasn’t yet confirmed what is the biological reason behind the reaction the experts don’t seem to be concerned.

 

“The research itself shows that regardless of the cause it is an MRI modification that is associated with a spike in activity in the brain.” Says Ravi Menon, a physicist, and neuroscientist at Western University in London, Canada. “I believe that’s the most important aspect, to begin with. More details could be discovered later.”

Ben Inglis, a physicist at the University of California, Berkeley is in agreement. This signal may be a result of blood flow, he claims however, ultimately the source isn’t important since the response is quick and efficient.

The main question right now is whether the latest data-acquisition technique can be applied to human FMRI scans. The DIANA method presumes that repeating events, like flashing lights, can impact the brain the same way each time. But someone who is awake may become bored or accustomed to the repetitive nature of the stimulus, Menon says, altering this reaction. Additionally, more complex mental processes, such as emotional reactions or decisions can affect brain activity over long durations and are difficult to activate in a reproducible way using quick and repetitive stimuli Inglis adds.

 

The research team is eager to see other researchers adopt this DIANA method. Co-author of the study Jeehyun Kwag who is an electrophysiologist from Seoul National University in South Korea believes that studying the brain’s connectivity, both structurally and functionally at the same time can transform the field.

“That could solve many unsolved issues in neuroscience,” she says.