In this, the third blog in a four blog series on epigenetics, I discuss behavioral epigenetics which studies how our environment causes changes in the epigenome of our brain cells. In the fourth and last blog in this series, I will talk about ways to reverse negative epigenetic changes.
Epigenetics drives biological functions as diverse as susceptibility to disease and memory. Hence, our environment, (nurture), interacts with our genes, (nature), to change our body and behaviors. Our environment begins at conception and includes, virtually everything that happens in our life to include, our social experiences, nutrition, hormones, exposure to toxins and stress.
Because behavioral epigenetics deals with changes to our brain cells, it has the potential to explain, and possibly solve medical problems like mental retardation, autism, schizophrenia, and neurodegenerative disorders. It may also help us address social challenges, like aging, addiction, suicide, child abuse, and child neglect. This is in part due to the fact that epigenetic modifications to a number of genes figure in learning and memory, which impact our behavior. For example, some research on fear conditioning, shows mice learning to act afraid of a particular location where they have been subjected to electric shocks. And, the formation of long-term memory requires that epigenetic processes induce lasting changes in gene expression in brain cells.
Severe chronic stress experienced during early life not only alters adult behavior in the animals subjected to the stress, but also impacts the behavior of the offspring across several generations. In mice experiments, the offspring of the animals directly subjected to stress manifest similar behavioral alterations, despite the fact that they were raised without the same type of stress. Both female and male mice transmitted the behavioral symptoms, independent of the care they received, due to alterations in epigenetic processes in several genes in the brains of the stressed animals and their offspring, as well as in the male sperm. And in some mouse studies, some epigenetic changes can persist to the fifth generation.
Our environment also includes our thoughts and emotions. This is visible in how different people respond to the same social and cultural situations. For example, how I respond to a strange dog walking towards me depends on my past experiences. If a dog bit me as a child and I see a large strange dog walking slowly in my direction, I may become very fearful. My fear will cause my body to produce cortisol, the “stress” hormone. You, however, may have had positive past experiences with dogs. Hence, upon seeing a large strange dog walking slowly towards you, you may be curious but not fearful. And, while you may pay close attention to what the dog is doing, depending on how the dog is acting, you may even look forward to meeting it. Because our thoughts and emotions are part of our environment, they can impact our physical and mental health.
This is true because events like an approaching large dog may cause thoughts that can create specific changes in our brain. This is possible because our brain cells use chemical messengers to send information to one another. Because we call our brain cells neurons, we call the chemical messengers, neurotransmitters. And, when our cells emit a neurotransmitter, the cell receiving the neurotransmitter uses a structure called a receptor to receive the message. A receptor functions as an on-off switch for a particular activity in a cell. When a substance comes along that fits into a receptor – like a key fitting into a lock – it turns the switch, which starts a specific activity in the cell.
There are thousands of receptors on each cell of our body. And, each receptor responds to a specific neurotransmitter. Feelings of anger, sadness, excitement, or happiness release different neurotransmitters. Once released, they move through the body connecting with the receptors designed to receive them. Once received, the transmitted messages change the structure of the receiving cell. And when cells receive a lot of neurotransmitters, they create more receptors. This increases their ability to receive and react to more of the same neurotransmitters.
Hence, bombarding our neurons with negative feelings, creates more receptors to receive negative feeling neurotransmitters. This makes them more sensitive to, and react faster to, future neurotransmitters from negative thoughts like when we are fearful. We also lessen the number of positive neurotransmitter receptors making it harder to respond to positive thoughts. The process of creating more receptors can lead to epigenetic changes.
As a result, experiences like child neglect, drug abuse or other severe stresses can cause epigenetic changes to the neurons of our brain. And, we can pass epigenetic changes on to our children. Hence, our children can inherit the impact of severe stresses in our lives.
While severe stress can cause negative epigenetic changes, positive nurturing touching, like gentle hugging, can cause positive changes and stimulate young brains for healthy growth. Hugs trigger the release of oxytocin that lowers stress hormone levels and can make a child feel loved. Hugging helps children learn to regulate their emotions and become more resilient. They also bolster optimism, boost self-esteem, increase trust, and improve relationships while reducing fear.
Just as nurturing touching can have beneficial effects, how we pay attention can have beneficial effects. This is because selecting relevant information is key to learning, and without attention, discovering a pattern in a pile of data is like looking for the fabled needle in a haystack.
Attention plays such a key role in selecting relevant information that it is present in many different circuits in the brain. However, if attention is misdirected, learning can get stuck.
Because paying attention involves suppressing unwanted information, our brain may become blind to what it chooses not to see. For example, in experiments like the “invisible gorilla,” inattention can cause us to not see part of an image. In the “invisible gorilla” experiment, people are asked to watch a short video of basketball players, dressed in black and white, pass a ball back and forth. The people’s task is to count, as precisely as possible, the number of passes by the white team.
While this seems easy, when asked: “Did you see the gorilla?” most people ask, “What gorilla?” When the video is rewound, people discover that an actor, in a full-body gorilla costume, walks across the stage and stops to pound on his chest for several seconds. It seems impossible to miss. Yet many people do not see it because their attention is focused on the white team and actively ignores distracting players dressed in black, like the gorilla. Busy with counting, the observer’s mental workspace is unable to see the gorilla. Psychologists call this phenomenon the “attentional blink”: our eyes may remain open, but our mind “blinks,” busy with its main task and unable to attend to anything else.
In these experiments, we suffer from two deficits. First, we fail to see the gorilla. Second, we are unaware of our own unawareness and may be convinced we have seen all there is to see. For example, many people, after the invisible gorilla experiment, cannot believe their own blindness and reason that if there really was a gorilla in the video, they would have seen it. This is false because our attention is extremely limited, and despite all our good will, when our thoughts are focused on one object, other objects, even important ones, can elude us and go unseen. The intrinsic limits of our awareness lead us to overestimate what we and others can perceive.
And, while I am not aware of research that speaks to the epigenetic effects of how we pay attention, the fact that our attention system involves the release of neuromodulators such as serotonin, acetylcholine, and dopamine, means how we pay attention may have epigenetic effects. Each of these neuromodulators has been shown to play a role in epigenetic changes. Hence, further research may show that how we pay attention can affect our epigenome.
What we do know, is that behavioral epigenetics tells us that who we are is the product of the things that happen to us in our life, because the things that happen in our lives change the way our genes operate. Behavioral epigenetics also means our thoughts, attitudes, and perceptions can control our biology since changing our thoughts and our physical environment can shape how our genes function. And, as I said in my last blog, just as chronic stress can change our brains for the worse, behaviors I engaged in in the past, like “exercise and meditation could have changed my brain so I could function at oxygen levels that where so low that they would cause most people to suffer brain damage.” Behavioral epigenetics, therefore, places us in the driver’s seat. It allows us to modify our behavior, how our genes operate, and influence the behavior of our descendants.
In my next blog, I will discuss ways to reverse negative epigenetic changes.