Humans are social beings, and it shouldn’t be surprising that there are specific groups of nerve cells in the brain that are directly influenced by social experiences. One important mechanism mediating these interactions is neuroplasticity, which involves the brain’s ability to modify connections between various groups of brain cells. In essence, the brain can rewire itself and adjust the degree to which certain regions communicate with each other. Neurogenesis, i.e., the ability of certain brain regions to generate new neurons, is another important mechanism involved in some forms of neuroplasticity. The pattern of connections that form between new brain cells and older cells is a powerful way that the brain can change in response to social and environmental experiences, and some evidence indicates that the new brain cells exert important regulatory actions over stress responses. The process of neuroplasticity is critical to all aspects of brain function, including those involving cognition, memory, emotions, and motivation.
“Social neuroscience” is a rapidly growing area of brain research that focuses on deciphering the mechanisms underlying interactions between interpersonal behavior and brain activity. Recently, the journal Nature Neuroscience published a series of review articles pertaining to social neuroscience. Some of the information described in this post is based on one of these review articles: “Social influences on neuroplasticity: stress and interventions to promote well-being” by Richard Davidson and Bruce McEwen.
During the process of development, there are specific time periods (so-called “critical periods”) when exposure to certain stimuli is needed in order for normal brain function to develop. For example, if a child has a “lazy eye” and it isn’t discovered early in life, the unaffected eye becomes dominant and the “lazy” eye may not develop the ability to see adequately. If the condition is discovered early, then patching the good eye allows the “lazy” eye to develop better vision.The ability to correct this visual defect becomes more difficult with age as the time window closes on the critical period for visual development. In terms of social and emotional development in humans, the nature and timing of such “critical periods” hasn’t been clearly defined. However, there is evidence that interventions in very young children may be more effective in minimizing the long-term symptoms of certain disorders such as autism than intervening when a person is older. Determining the nature of critical periods that are relevant to specific forms of social and emotional development is an important area of current and future research.
Early childhood experiences can strongly influence a person’s long-term ability to interact with other people. Being exposed to highly stressful adverse events early in life can negatively impact how we handle stress and interact with others later in life. Genes play an important role in this adaptation, and some people inherit the ability to tolerate adverse circumstances better than others. Genes and environment are constantly interacting and shaping the brain’s ability to adjust. Interestingly, there is some evidence from research with squirrel monkeys that occasional mild stress in young animals has beneficial effects, increasing exploratory behaviors and independence as they mature.
Evidence from other animal studies indicates that chronic significant stressors can decrease the connections in brain regions involved in memory and higher order information processing, such as the hippocampus and prefrontal cortex. However, the same chronic stressors actually increase connectivity between cells in areas of brain involved in emotion, such as the amygdala and orbitofrontal cortex. Some of these regions also change their overall size in response to chronic stressors.
Importantly, certain positive interventions can help re-establish normal connections among these various brain regions following exposure to stress. Physical activity, environmental enrichment, and decreasing stress levels can all lead to a reversal of stress-induced changes in brain connections. Once again, exercise proves to be beneficial to our mental health. Voluntary exercise is also an interesting example of a form of controlled stress that can result in positive effects on both body and brain function.
Certain psychotherapies, for example, cognitive behavior therapy, can help people with illnesses such as depression or anxiety disorders. These therapies likely influence brain connections through learning and enhanced attentional processing. Anti-depressant medications also have been shown to reverse stress-induced connectivity changes in the hippocampus.
There are also certain medications that more directly influence the brain’s ability to undergo neuroplasticity, and it is likely that new drugs will be developed that have specific effects on neuroplastic mechanisms. It is possible that therapies will be developed that specifically utilize neuroplasticity-altering medication during behavioral or psychotherapeutic sessions. Administering these medications concurrent with the therapy might enhance the effectiveness of the therapy in producing behavioral improvement. This is an area where much more research is needed, but early results with the drug D-cycloserine are encouraging.
Being able to modify neuroplastic changes in the brain and reverse abnormal patterns of connections has the potential to dramatically influence the ability to effectively treat persons with a variety of psychiatric illnesses. Such approaches may also be applicable to helping people whose brain wiring has been altered by addiction to various drugs.
This column was co-written by Eugene Rubin MD, PhD and Charles Zorumski MD.