Most animals (from roundworms to people) favor the more predictable option when faced with getting resources to help them survive (such as food).
Scientists from the Salk Molecular Neurobiology Laboratory, La Jolla, Calif, have found the basis for how animals weigh learning and risk-taking behavior to secure a more predictable environment. Their findings shed light on the function of two chemical signals that are key to human behavior: dopamine, which is responsible for reward and risk-taking--and CREB, needed for learning.
"Previous research has shown that certain neurons respond to changes in light to determine variability in their environment, but that's not the only mechanism," says senior author Sreekanth Chalasani, PhD, assistant professor. "We discovered a new mechanism that evaluates environmental variability, a skill crucial to animals' survival."
The researchers, studying roundworms (Caenorhabditis elegans), traced how this new circuit employs information from the animal's senses to determine how predictable the environment is and compel the worm to go somewhere else, if necessary.
They say that the circuit, comprised of 16 of the 302 neurons in the worm's brain, probably has parallels in more intricate animal brains and might be a starting point to understanding and fixing some psychiatric or behavioral disorders.
The team found that two pairs of high-threshold neurons in this learning circuit act as gatekeepers, with one pair reacting to hefty increases of the presence of food and the other pair reacting to large decreases. When either of the neurons recognizes a sizable change in an environment, they prompt other neurons to release the neurotransmitter dopamine.
Depositing dopamine onto a brain (whether roundworm or human) ups the willingness to take risks.
"The connection between dopamine and risk is conserved across animals and is already known, but we showed mechanistically how it works," says Chalasani, who also holds the Helen McLoraine Developmental Chair in Neurobiology. "We hope this work will lead to better therapies for neurodegenerative and behavioral diseases and other disorders where dopamine signaling is irregular."
When the protein CREB occurred in larger amounts, the worms learned faster about food variability. "Normally the worms took about 30 minutes or so to explore and learn about food, but as you keep increasing the CREB protein they learn it faster," Chalasani says. "So dopamine stores the memory of what these worms learn while CREB regulates how quickly they learn."
The article "Neural Mechanisms for Evaluating Environmental Variability in Caenorhabditis elegans," is in the April 9, 2015 issue of Neuron.
[Source: Salk Institute for Biological Studies]