Whether it’s responding to a good experience or a bad one, the brain’s reward center is the home of the “thrill” in thrill-seeking behavior – even if it’s just the thrill of surviving it, say scientists at Georgia Health Sciences University and East China Normal University. The findings are published in PLoS One.
Eating chocolate or falling off a building — or just the thought of either — can trigger the release of dopamine, a neurotransmitter that can get the heart racing and motivate behavior, according to Joe Z. Tsien, Ph.D., co-director of GHSU’s Brain & Behavior Discovery Institute.
Scientists examined dopamine neurons in the ventral tegmental area of the mouse brain; this area is commonly studied for its role in reward-related motivation or drug addiction. The researchers found virtually all the cells had some response to a good or bad experience, but a terrifying event excited about 25 percent of the neurons, initiating more dopamine production.
Tsien noted that this response lasted as long as the event and that context was also important. Scientists issued a conditioned sound to associate a certain setting with a good or bad event, and later, all it took was the sound in that setting to evoke the same dopamine response in the mice.
“We have believed that dopamine was always engaged in reward and processing the hedonic feeling,” says Tsien. “What we have found is that dopamine neurons also are stimulated or respond to negative events.”
Just how chocolate or jumping off a building induces dopamine production is still unkown. “That is just the way the brain is wired,” Tsien said.
Genetics can have an influence on the number of cells activated by scary events, Tsien said, and although more interpretation is needed, the findings could help explain some harmful behaviors, such as drug addiction or other risky actions.
In another paper, Tsien and his colleagues at Boston University explored how a brain decides which information, whether good or bad, it needs to remember. They recorded hundreds of mouse brain cells in a region called CA1-, found in the hippocampus, and showed that all are involved in sensing what happens, but in different ways.
For example, the scientists found that during a major event, such as a strong earthquake, cells triggered a larger sensory response than they did during a mild earthquake. However, a little less than half of these cells had a more consistent neural response to all events, whether big or small. These are known as “invariant cells” because of their consistent actions no matter the intensity of the event. Tsien said these cells are vital in helping the brain remember events.
Interestingly, the initial even-keeled sensory response was followed by the cells replaying the experience. It’s the cells’ reverberation that corresponds with learning and memory. “If they play it over and over, you can remember it for a long time,” said Tsien.
However, these steadier cells vary in that some continue to replay specific memories while the majority focus on more general moments within the event. “The general-knowledge cells have the ‘highest volume,’” Tsien said. “So we walk away with general knowledge that will guide your life, which is more important than the details.”
Genetics most likely play a role in a person’s specific ratio of cells that would encode general versus more detailed memories, Tsien said. For example, someone with a photographic memory probably has more of the specific memory makers; those with autism or schizophrenia may have fewer of the general memory makers that would help someone understand context and complex relationships.