Scientists now know the brain chemistry behind Pavlov’s famous dog experiment

The revealing history of the humble market.
The revealing history of the humble market.
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From choosing coffee or tea to caffeinate yourself in the morning to how you plan to unwind after the day’s end, we make decisions of varying degrees of importance every day.

Yet for such a routine activity, scientists know little about what’s going on at a chemical level as we make these choices.

Teams from the University of California, Los Angeles, the University of California, San Diego, and the Icahn School of Medicine in New York have found a way to take a close look at the way neurotransmitters fire in mouse brains as they learn certain behaviors.  Their research presented today (August 22) in Philadelphia at the American Chemical Society’s annual meeting.

“We were able to measure the timing of dopamine surges during the learning process,” Paul Slesinger, a neuroscientist at the Icahn School of Medicine, said in a press release.

Slesinger and his team developed tiny chemicals called cell-based neurotransmitter fluorescent engineered reporters, or CNiFERs (pronounced ‘sniffers’) and implanted them in mouse cortexes, the part of the brain that has been associated with learning and decision-making. These proteins became illuminated when they detected the neurotransmitters dopamine and norepinephrine. These signals have been known to play a part in how we make decisions: They’re released when we feel pleasure as part of our neural reward system and when we feel prepared to take action, respectively.

The researchers conditioned mice to teach them that when they heard a particular sound, they would be rewarded with sugar. They could see in real-time as the different neurotransmitters were produced, and how the timing of the release of these signals changed over time as the mice learned. ”We could see the dopamine signal was measured initially right after the reward. Then after days of training, we started to detect dopamine after the tone but before the reward was presented,” Slesinger said.

Previous research at the way we make decisions has mostly come from functional magnetic resonance imaging (fMRI). These images of the brain show where blood is flowing, which indicates that oxygen is being transported to certain regions as they’re being used. Looking at the chemical signaling itself, though, could give researchers a much clearer picture of the exact process.

Ultimately, this could lead to treatments for people for whom these pathways are disrupted, said Anne Andrews, a neuroscientist at UCLA, said in a press conference. Andrews and her team are developing similar chemicals that detect neurotransmitters that use an electrical mechanism that could eventually be used in tandem with deep brain stimulation, a treatment for Parkinson’s Disease.

Although these neurotransmitter detection methods are only applicable in mouse models at the moment, they show how brain signaling may change as we learn, and make decisions based on what we know, over time. “We can now monitor these decision making cues—or thoughts, if you will—in real time, and then see the actions on the animal,” Slesinger said.