RatCAP: mini wearable brain scanner links neurochemisty with behaviour

A new portable brain scanner for rats can, for the first time, show how brain activity influences behaviour.

Positron emission tomography (PET) imaging help researchers look into brain activity – by measuring flashes of light to reveal blood flow.

Now, scientists have created a PET scanner that’s small enough for rats to wear.

Because it fits on rats while they’re awake and moving around, the new tech assesses brain function and behavior at the same time – allowing a glimpse of all the info lost when looking at behavior and neurochemistry separately and as they say, this can eventually help researchers better understand functions in the human brain.

“It means we can watch how the animals behave and observe their brain chemistry at the same time,” says study author David Schlyer of Brookhaven National Laboratory (BNL).

PET scans use injections of very small amounts of radiopharmaceuticals to show the metabolism of chemicals in real time. In addition to brain activity and blood flow, it helps in examining organ function, uncovering drug addiction or depression, diagnosing cancer early, and researching neurological conditions from Alzheimer’s disease to epilepsy.

In humans, it’s pretty straightforward to use. Just lie down and relax. But rats can’t really stay still inside an imaging scanner without being restrained, paralyzed, or anesthetized – ruling out many types of studies.
The team engineered a mini PET scan – known as RatCAP for Rat Conscious Animal PET (pictured). It’s about 38mm in diameter and weighs 250g.

Most importantly, it allows neuroscientists to study molecular processes that occur in the brain during consciousness.

“It’s a methodological issue,” says study author Paul Vaska of BNL. “If you start to make assumptions that what you’re seeing under anesthesia is what you’ll see awake, you may make a mistake in your interpretation.”

Other techniques to simultaneously track brain function and behavior, such as the more invasive in vivo microdialysis, which involves inserting a probe into brain tissue, are limited to small regions of the brain.

The RatCAP, by contrast, allows researchers to look globally across the brain.

For the inaugural test, the team decided to look at the neurotransmitter dopamine, comparing levels in anesthetized rats using conventional PET with those in awake rats using the RatCAP:

• Unexpectedly, dopamine levels in the awake rats were lower. (More behavioural activity would traditionally be associated with higher levels of dopamine.)
• There was a strong correlation between dopamine levels and behavioral activity – like head turns and body motion.
• Changes can be monitored on a minute-to-minute basis. (Currently, PET studies tend to average 30 to 60 minutes.)

“We can study changes in dopamine connected to drug abuse,” says first author Daniela Schulz of BNL, “but also the effect of change in other psychiatric disorders where proteins in the brain are important, like schizophrenia, attention deficit hyperactivity disorder and depression.”

The team hopes to develop wearable scanners for people and monkeys, so they too can move around and engage in activities while their brains are being scanned.

“We’re considering this at the moment,” says Schlyer. “It would be something like a football helmet.”

The study was published in Nature Methods this week.