Adrenaline bursts could help us learn when we are surprised: MIT study

Good news for adrenaline junkies.

An adrenaline burst could help scientists learn when we experience surprises due to the hormone noradrenaline, or norepinephrine.

A study conducted at the Massachusetts Institute of Technology, published in “Nature,” discovered that the hormone, which also serves as a neurotransmitter, is released when we need to focus on or pay attention to something of importance.

While it’s produced deep in the brain within a structure called the locus coeruleus, it can help stimulate rewarding behavior.

In other words, it plays into learning behaviors through trial, error and reward.

Scientists tested this phenomenon on mice in a new study, where they looked at reinforcement learning.

Researchers trained mice to push on a lever when a high-frequency tone sounded, but not with a low-frequency one. When the mice performed correctly, they received a reward – water – but if they made the incorrect movement, they were given an undesirable puff of air.

Through the experiment, the rodents also learned to push harder with a louder sound, growing confused when the sound was quiet.

To test their theories of noradrenaline, they inhibited the locus coeruleus, which controls the hormone, resulting in the mice becoming hesitant to push the lever when low-volume sounds played. The researchers suggested the hormone made them more likely to take a risk in order to gain a reward, even in circumstances when they were unsure if they would receive one.

In short, scientists believe the structure in the brain signals that if the lever is pushed, the mice will be rewarded.

“The animal is pushing because it wants a reward, and the locus coeruleus provides critical signals to say, push now, because the reward will come,” the study’s senior author Professor Mriganka Sur told SWNN.

Through the experiment, researchers discovered that the neurons that create noradrenaline sent most of their output to the motor cortex, which causes behavioral functions. A second burst of adrenaline, then, comes after the lever is pushed.

While scientists predicted that the second output of hormones would be smaller, they were surprised when it was, in fact, larger. It was also found to spread to other parts of the brain, not just one, including the prefrontal cortex, which controls planning and other cognitive functions.

“What this work shows is that the locus coeruleus encodes unexpected events, and paying attention to those surprising events is crucial for the brain to take stock of its environment,” said Sur.

The animal, then, is “constantly adjusting its behavior,” even though it had already learned the task at hand.

In later trials, scientists saw that the mice would be more hesitant to push the lever when a reward wasn’t promised.

“Neuromodulatory substances are thought to perfuse large areas of the brain and thereby alter the excitatory or inhibitory drive that neurons are receiving in a more point-to-point fashion,” Sur continued. “This suggests they must have very crucial brain-wide functions that are important for survival and for brain state regulation.”

But noradrenaline isn’t the only hormone that influences brain activity as a neuromodulator – such as dopamine, serotonin and acetylcholine, which have more general effects because they influence large portions of the brain.

While various dopamine studies have been conducted about its role in the brain — especially when it comes to motivation and reward — noradrenaline is less studied. The hormone has been linked to both arousal and alertness, yet overloading can cause anxiety.

“The surprise-encoding function of the locus coeruleus seem to be much more widespread in the brain, and that may make sense because everything we do is moderated by surprise,” said Sur.

Now, his team wants to study the relationship between noradrenaline and the well-studied hormone dopamine.