It's not front-page news that our brains are the seat of our thoughts and emotions. The brain is the body's decision maker, pilot of the action, and engineer that keeps all systems running. The brain adapts the body's behavior to its environment, absorbs sensory input, and directs appropriate and timely responses. For a long time, we attributed the amazing function of the brain to its complex structure made up of highly specialized cells, and neurons. These structures are the hardware of the brain.

But at a much deeper level, new genomic studies show that emotions and behaviors are shaped by a second layer of tissue in the brain, something we only recently did with sight. It depends on your genes.

The driver's seat neuron

We now know that the approximately 100 billion neurons in the human brain are interconnected to form complex circuits that carry electrical and chemical messages to generate memories and direct actions. It is the physical structure, the hardware of our neural control system, and is based on scientific tools of the time, replicated through experience.

During the 20th century, dozens of scientists described the sugars, lipids, proteins, and countless other molecules that makeup, function and repair our brains. These molecules seemed to be overlooked. They appear to play a supporting role in the neurons that control our behavior.

Genes are translated into proteins that play important roles in the brain. 

A new take on genes

But 21st-century genomics has revealed another surprise about the brain. Genomics studies the complete genetic information of a cell, the activity of its genes, and the interactions between them. Genomics has revealed that genes in the brain are more involved in regulating behavior than previously thought.

Genes direct the production of the aforementioned brain molecules through RNA intermediates. RNA molecules tell the cell's machinery when and how to make the proteins it needs to grow and function. Techniques developed over the past two decades allow researchers to precisely monitor the ebb and flow of RNA produced by each gene in the brain. These studies revealed a remarkably close relationship between behavior and gene activity in the brain.

Some of the earliest insights into the intimate relationship between behavior and brain gene activity came from an unexpected source: the honeybee brain. Bees, like humans, live in complex societies and are greatly influenced by the behavior of those around them.

The influence of genes on the brain

Why are brain gene activity and behavior closely related? The tips come from other bee studies. Bees react aggressively as soon as the nest is threatened. Long delays in the wild can be fatal. This behavioral response is much faster than the time it takes to generate a new RNA molecule, indicating that the initial response is more neurological than genomic. However, our lab found changes in the activity of hundreds of genes in the brains of individual bees in response to hive pests hours after the threat was neutralized. Dangerous experiences have changed them both molecularly and behaviorally.

At the same time as the steady change in brain gene activity, seen through changes in the size of each type of RNA molecule, there was also a steady increase in the arousal of the once-excited bees. This is logical. Past performance doesn't necessarily predict future Wall Street performance, but it's safe to take the risk and be cautious. Experimental manipulations that shape brain gene activity profiles after invasion made naïve bees aggressive, demonstrating a causal relationship between brain gene activity and behavior. Faced with a potentially recurring threat, the bee's brain has genomic applications to help it respond more effectively.

Both systems work together

Neurons in the brain and the genome, hardware, and software within them together regulate a person's response to new situations that may differ from person to person. The same dramatic event (a problem at school or work, a new person in a social circle) can be very stressful for some and a little stressful for others. We now suspect that the nervous systems of these two individuals may have been genetically regulated differently. Perhaps it is the result of various stressful experiences in the past. In a living brain, unlike a computer, the software can help change the hardware, and as new conditions arise, the operation of the neural hardware continues to alter the genomic software. Nature has invented an 'intelligent' system where hardware and software dynamically adapt and interact!

These interactions between genes and neurons are based on a history of ever-increasing interdependence that goes back to inherited individual differences in temperament, which also affect gene activity. Acute stress can cause genomic changes that cause fear and anger for hours, but chronic stress from bereavement or abuse can have harmful effects on health because it activates genomic changes in the brain that are not reversible. In some cases, it causes long-term changes in the chemical structure of DNA. These changes, called epigenetics, can also be passed down from one generation to the next.