Man is by nature a social animal, so begins the legendary quote by Aristotle, the famed ancient Greek philosopher. It has long been proven that loneliness is not good for humans. In 2016, scientists found the physical locus of loneliness in the brain, and now, it has been discovered that the stress of chronic social isolation can actually reshape the brain, causing feelings of aggression and fear.
Experts at the California Institute of Technology have discovered a specific chemical that accumulates in the brain as a result of chronic social isolation. In humans, social isolation is linked to crippling mental health issues such as depression and post-traumatic stress disorder. Blocking the chemical buildup in the brain that results from seclusion could ultimately lead to a method of treating mental health disorders.
According to the study published the journal Cell, the research, conducted in the laboratory of David J Anderson, was based on previous observations of social isolation in mice and the resulting behavioural changes. In response to seclusion, mice show increased aggression, persistent fear, and hypersensitivity to threatening stimuli. For example, mice that have been socially isolated will remain frozen in place long after a potential threat has passed. These effects are not seen as result of short-term isolation, suggesting that chronic isolation is what causes the changes in aggression and fear responses.
Previous research in the Anderson laboratory had uncovered a particular neurochemical called tachykinin that plays a role in promoting aggression in socially isolated flies. Tachykinin is a neuropeptide that is released when certain neurons are activated. Neuropeptides alter the properties of other neurons when they bind to specific receptors, which have an impact on neural circuit function.
In mice, the tachykinin gene Tac2 encodes a neuropeptide called neurokinin B (NkB). Tac2 and NkB are produced by neurons in specific regions of a mouse’s brain – the amygdala and the hypothalamus – which are involved in emotional and social behaviour. The researchers found that chronic social isolation caused an increase in Tac2 gene expression and the production of NkB. When they administered a drug to chemically block NkB-specific receptors, the negative effects of isolation were eliminated and anxious mice began behaving normally.
The researchers also found that suppressing the Tac2 gene in the amygdala eliminated behaviours associated with fear, but not aggression. On the other hand, suppressing the gene in the hypothalamus eliminated increased aggression but not persistent fear. This finding indicates that various effects of social isolation are produced as Tac2 increases in different brain regions. Study lead author Moriel Zelikowsky explained that humans have a signalling system comparable to the Tac2 system in mice, so this research may have potential applications for treating mental health disorders such as chronic stress.
The antagonist drug the team gave the mice during their periods of isolation effectively lessened the negative effects of the isolation. This suggests that, while the effects of loneliness show up as psychological stress, they can be managed with neuroscience and pharmacology. The study also underlines the brain’s ability to adapt to environmental changes – a phenomenon known as brain plasticity. Previous research has found prolonged loneliness can transform the brain in a way that makes people less able to relate to others.
