In the article, "Preference for cocaine-versus pup-associated cues differentially activates neurons expressing either Fos or CART in lactating, maternal rodents," which is in press for the September 2005 volume of the journal Neuroscience (the article currently appears online at www.sciencedirect.com) Rutgers-Newark neuroscience professor Joan Morrell and her colleague Brandi Mattson reveal that individual preferences can be linked to the activation of specific sets of neurons within the brain. The researchers used postpartum rats in order to establish preferences and analyze how the mother rats' brains functioned when they selected an environment associated with their pups or another environment associated with the drug cocaine. In the experiment, rats learned over four days in which distinct environments they had access to their pups versus where they had access to cocaine. Following a 24-hour wait, the rats were given the opportunity to choose either the environment where they anticipated they would find either their pups or where they would find cocaine.
Using a computer program, the researchers recorded the rats' time and activity in each chamber as a means of determining their preferences for pups or cocaine. Then, the researchers analyzed and recorded the rats' brain activity at the time of their environmental choice.
According to Dr. Morrell, the analysis revealed clear patterns of neuronal activity when the rats made their choices and showed that specific brain regions were active when the animals were making one choice (pup-associated environment) in favor of another one (drug-associated environment). The researchers determined this by tracking the presence of proteins that demonstrate the activity of neurons within the brain.
"This approach provides a snapshot of what was going on in the brain at decision time, which is preferred pups or cocaine," Dr. Morrell notes. "The different brain regions are arranged in a circuit, with some regions more active or less active depending on what the rat's preference is. Understanding what is going on in the brain at decision time is crucial since preference for the environment related to her pups is likely to lead to pup care by the mother rat while preference for the environment related to cocaine is likely to lead to pup neglect."
These findings may be significant because they establish a link between individual preferences and innate brain activity, but Dr. Morrell cautioned that it would be a leap to use these results to provide a model for the higher cognitive processes such as critical thinking and belief systems that humans possess."
"However, my results do demonstrate the general principles of how the nervous system mediates such important decisions and these principles apply in the nervous system of all mammals including humans," Dr. Morrell explains. "With this approach we can determine the ground rules for the function of the mammalian brain in such decisions."
Journal
Neuroscience