The occurrence of surprise can be attributed to an unforeseen alteration in the chemical makeup of the brain.

A recent study published in the journal Nature suggests that when we experience surprise, our brains are more likely to be attentive. Researchers, from the Massachusetts Institute of Technology, discovered that a hormone called noradrenaline can impact brain activity and behavior in response to unexpected events. Noradrenaline is one of several chemicals that can produce intense signals in the brain and has been linked to feelings of excitement, anxiety, and alertness, as well as contributing to the learning process. However, the study shows that noradrenaline also plays a significant role in how we respond to unexpected situations.

The M.I.T.group used a method called optogenetics to study noradrenaline in mice. The researchers included unique light-sensitive proteins in neurons that function as an “off button” for the cells when struck by pulses of laser light. The researchers directed their attention towards altering the locus coeruleus, a region of the brain that contains cells responsible for releasing noradrenaline. By using lasers, they were able to inhibit these cells from producing the hormone under specific conditions. They combined this method with photo tagging, a technique that involves illuminating proteins with light to monitor the activity in the locus coeruleus cells and to determine the amount of noradrenaline produced.

The researchers designed a learning task for the rodents involving trial and error. The task required the mice to press a lever when they heard a particular noise. There were two different types of sounds used in the experiment, with high-frequency tones of around twelve kilohertz followed by the reward of water when the mice pressed the lever. In contrast, when the mice pressed the lever after hearing low-frequency tones of about four kilohertz, they were surprised by a discomforting puff of air blown at them. Over time, the mice learned to associate the high-frequency tones with the reward of water and therefore pressed the lever when they heard this type of sound. Conversely, they avoided pressing the lever when they heard low-frequency tones due to the negative consequence of the puff of air.

Upon analyzing the activity in the locus coeruleus during the learning task, the researchers observed that there were two distinct moments when the production of noradrenaline increased. The first was before the mice pressed the lever, and the second was when they received either water or a puff of air. The researchers hypothesize that the initial surge of noradrenaline may indicate its involvement in the animal’s decision-making process when pursuing rewards.

 One of their experiments supports that hunch. When the researchers lowered the volume of the tones, making it more difficult for the mice to distinguish between the high-frequency tones that produced water and the low-frequency tones that caused the puff of air, the mice became perplexed. While some of them still attempted to press the lever, others were hesitant to do so. The researchers then used the optogenetic off switch to inhibit the release of noradrenaline, which further reduced the mice’s willingness to take risks. It appeared that the release of noradrenaline increased the likelihood that the mice would take risks when they were uncertain about the outcome.

Additionally, the researchers tracked the noradrenaline released before mice hit the lever and found it traveled to the brain’s motor cortex, an area involved in sending nerve impulses that stimulate muscle movement. To put it differently, the increase in brain chemistry helped to motivate the mice to press the lever. Future studies can explore whether similar processes occur in humans. Researchers can also examine how noradrenaline interacts with other chemical messengers, such as dopamine, which also play a role in our response to rewards. This new research suggests that the “element of surprise” may have a much more intricate neurochemical basis than previously thought.

Read the original article on Scientific American.