One major point of contention among psychologists has always been the nature versus nurture debate -- the extent to which particular aspects of our behavior are a product of either inherited (i.e. genetic) or acquired (i.e. learned) influences. In a new study on mice, researchers at the University of Utah Health focused on the former, showing that genes inherited from each parent have their own impact on hormones and important neurotransmitters that regulate our mood and behavior.
Intriguingly, some of these genetic influences are sex-specific. For instance, the scientists found that genetics inherited from mom can shape the decisions and actions of sons, while genes from dad have biased control over daughters.
I got it from my Mom and Dad
Like chromosomes, genes also come in pairs. Both mom and dad each have two copies, or alleles, of each of their genes, but each parent only passes along one copy of each to the child. These genes determine many traits, such as hair and skin color.
But it's not only our outward appearance that is influenced by genes. In a new study, researchers found that tyrosine hydroxylase and dopa decarboxylase -- two genes that are heavily involved in the synthesis of hormones and neurotransmitters like dopamine, serotonin, norepinephrine, or epinephrine -- are expressed differently from maternally versus paternally inherited gene copies. These chemicals play a crucial role in regulating an array of important functions from mood to movement.
The genes are also involved in the production of the adrenaline hormone by the adrenal gland, which triggers the "fight or flight" response when we encounter danger or stress. Together, these pathways form the brain-adrenal axis.
"The brain-adrenal axis controls decision making, stress responses, and the release of adrenaline, sometimes called the fight or flight response. Our study shows how mom’s and dad’s genes control this axis in their offspring and affect adrenaline release. Mom’s control the brain and dad’s control the adrenal gland," Christopher Gregg, principal investigator and associate professor in the Department of Neurobiology at the University of Utah Health, told ZME Science.
In order to investigate how inherited gene copies introduce maternal or paternal biases in the brain-adrenal axis, the researchers genetically modified mice to attach a fluorescent tag to the dopa decarboxylase enzyme. Using a microscope, they could tell if a gene was inherited from the mother (colored red) or from the father (colored blue).
An investigation of the entire mouse brain revealed 11 regions that contained groups of neurons that only use mom's copy of the dopa decarboxylase gene. Conversely, in the adrenal gland, there were groups of cells that were exclusively expressed by the gene copy inherited from the dad.
These findings immediately led to an existential question: could our behavior be influenced by these genetic biases? To answer, the researchers analyzed mice with mutations that switched off one parent's copy in a select group of cells while the rodents were foraging for food.
The mice were left to explore freely so any external influence was kept to a minimum. Their behavior had to be as natural as possible as they encountered various obstacles, which prompted them to either take risks or retreat to safety, before resuming their quest for finding food.
These movements and behaviors look random and chaotic, but a machine algorithm developed by the researchers was able to pick up subtle, but significant patterns. When these foraging patterns were broken down into modules, the researchers were able to identify behavioral differences associated with each parent's copy of the dopa decarboxylase genes.
"We have faced a lot of skepticism from the scientific community. The way we study decision-making by using machine learning to detect patterns was hard for scientists to understand. The community was surprised to find that such well-studied genes (Th and Ddc) express the Mum and Dad’s gene copies in different brain and adrenal cells. We had to do a lot of work to show how strong the evidence is for our discovery," Gregg said.
Gregg had been interested in how biological factors influence our decisions since he first came across Daniel Kahneman's work in behavioral economics while he was still a postdoc. In the 1970s, Kahneman and Amos Tversky introduced the term 'cognitive bias' to describe our systematic but flawed patterns of responses to judgment and decision problems.
For instance, the gambler's fallacy makes us tend to be certain that if a coin has landed heads up five times in a row, then it's much more likely to land tails up the sixth time. The odds are, in fact, still 50-50. One of the most pervasive and damaging biases is the confirmation bias, which leads us to look for evidence confirming what we already think or suspect. If you're disgruntled by the current political divides across the world, where each side seems unable to allow that the other side might be right about some things, you can point the finger at confirmation bias in many cases. There are many other biases, though, with Wikipedia listing at least 185 entries.
Now, Gregg seems convinced that these cognitive biases and some decision processes are deeply rooted in our biology, as well as that of other mammals. And with more research, it may be possible to modify maladaptive behaviors in a clinical setting, with potential new treatments for conditions like anxiety or depression.
The main caveat, however, is that all of this work has been performed on mice. Gregg and colleagues now want to develop and apply a new artificial intelligence platform called Storyline Health to human decision-making and behavior. They expect to discover genetic factors that control our behavior and cognition in a similar way to rodents.
"I am very excited about this new area that emerges from our work and merges decision making, machine learning and genetics. We are going to discover a lot of important new things about the factors that shape our decisions," he said.
The findings appeared in the journal Cell Reports.