For decades, scientists and psychologists hinted at the link between mental health and physical health. While Stony Brook University Associate Professor of Integrative Neuroscience Dr. Turhan Canli explained the anecdotal evidence of centenarians being more social than their counterparts, his work focuses primarily on molecular characteristics of individuals with certain personality traits and the correlation of those characteristics with physical health.
One of the major studies in Canli’s lab focuses on the link between loneliness and health. A study published by Dr. John Cacioppo found that college-aged women who were lonely had reduced activity in the nucleus accumbens region when shown positive pictures of people in social groups, compared to their non-lonely counterparts. The nucleus accumbens region is a reward center in the brain that is activated by pleasurable activities.
It is important to note that loneliness does not necessarily correlate with the number of people a person knows. Some people prefer to be alone while others can have a big social group but still feel lonely. Therefore, individuals are characterized as lonely through self-reports, corroborated by psychological analyses.
Canli and his lab group aimed to further elucidate upon Cacioppo’s findings by studying gene expression in this portion of the brain. To do this, Canli collaborated with a brain bank in Chicago, which supplied him with post-mortem brain tissues from the nucleus accumbens of people who were and were not lonely.
Most brain banks have a specific subset of patients that they use and they contact the patient’s family members for information after the patient’s death. The brain bank that Canli used is unique in that they recruit people while they are still living. Therefore, the bank is able to profile the patients via self-reported information and assessments. This allows scientists to conduct tailored experiments involving personality traits that were not possible before.
Canli used a microarray with the tissues he received. Microarrays are chips on which various different tissue samples are placed. The microarrays are then analyzed using a wide variety of probes, resulting in a numerical quantification of the expression of different genes. After analyzing the raw data and comparing between the samples of both lonely and socially connected people, Canli found that when comparing expression in mRNA microarrays, there were 1,300 differentially expressed genes between the two groups.
Focusing on the most differentially expressed gene, he saw no significant difference in the DNA sequence despite differences in mRNA expression. This difference in gene expression at the DNA and mRNA level may be puzzling at first, but can be explained by epigenetics. The root word “epi” means above. Therefore, epigenetics are changes that occur on a scale above the DNA sequence. Epigenetics involve the influence of non-DNA molecules, like a methyl group, on DNA.
These changes are thought to be a product of environmental conditions. Thus, while the genes that would be expressed from the DNA sequence might be the same, epigenetic factors can alter the mRNA resulting in different gene expression. Therefore, it is likely that the role of epigenetics results in different gene expression in brains of lonely people, compared to brains of people who are not lonely.
Even more interesting is the implication of the 1,300 genes that were differentially expressed. Among the genes that had different expression levels in the brains of lonely people are genes associated with psychological disorders like depression. The large set of genes also includes genes associated with health problems like cancer, increased inflammation and an increased likelihood to contract an infection.
Loneliness appears to play a direct molecular role in emotional and physical problems. Canli even found that those who were lonely had a gene expression pattern suggesting an increased likelihood of dementia and a more rapid decline with Alzheimer’s disease. As Canli summarized, “loneliness precedes poorer health later in life.”
These findings elucidate part of the connection between personality, environmental factors and epigenetic changes, which result in differential gene expression and ultimately differences in physical and mental health. They also raise questions for future studies.
Canli hopes to further examine the hereditary and epigenetic role of groups of genes that were differentially expressed. By utilizing new tools to better understand the link between physical and mental health, scientists hope to create better treatment options and medicines. Canli said he hopes his work will spark interest worldwide and, “begin a field devoted to the neurogenetics of behavior.”
