Updated: Mar 14, 2021
Pune, Maharashtra, India
Figure 1: Insect Collection
Alongside the 2019 pandemic that started in Wuhan, we also saw some of the most rigorous lockdowns span from one country to another. For many of us, this was the first time that we were subjected to such harsh conditions of social distancing which turned into social isolation. Although we turned to the digital world to extend our support and share our feelings, the loneliness hiding behind our masks slowly crept in. Even before the pandemic, the covert loneliness resulting from different forms of isolation has had draconian effects on the mental health of the masses. When an organism is completely deprived of interacting with other members of its species, the resulting condition is termed Social Isolation. In humans and other vertebrates, social isolation hinders development, causes hyperactivity, weakened immunity, reduced sleep, and even early deaths. Surprisingly, social isolation has strikingly similar effects on social insects. When we speak about social insects we often imagine bees and ants (Fig. 2). However, these aren't the only insects that are social. In fact, insect sociality is measured by the degree to which certain behaviours occur. While many social insects live in groups or colonies, in truly social or ‘eusocial’ insects like bees, termites, and ants, colonies exhibit characteristics like collective care of the young, sharing of a common nest, the simultaneous occurrence of different developmental stages like adults, larvae and eggs, and division of labour with a working class that is usually sterile. The different labour divisions are commonly referred to as different ‘castes’ by scientists.
Interestingly, many studies have shown that different castes have different brain sizes corresponding to their social roles in insect colonies, and deprivation of social interaction has the gravest effect in those members that are required to carry out tasks that entail the most amount of socializing.
Being social animals ourselves, we thrive on social contact. It facilitates better brain development and function by reaffirming the growth and strengthening of certain neuronal pathways. Long periods of social isolation are known to cause depression, anxiety, and an increased risk of many diseases. Thereupon arises the question of whether our brains show altered physical states as a consequence of social deprivation.
Figure 2: Bees and ants communicating with colony members via physical contact.
Does isolation change the brain?
It is proven that along with environmental factors, larger brain sizes and volumes can be attributed to increasing social complexity in insects. There are a number of studies focusing on how social isolation in insects affects the brain. One such study conducted on the Florida carpenter ant, Camponotus floridanus, focused on how social isolation in ants affects their behaviour and their brain. The study found that the brains of socially isolated ants differ structurally from the brains of ants that were allowed to fraternize. The isolated ants were slower, less active, less aggressive, and less interested in engaging with other ants. The study showed the impact of isolation on structures called ‘mushroom bodies’ (MSBs; Fig. 3) situated in the ant brain, made up of thousands of neurons called Kenyon cells. MSBs are associated with different types of memory and learning like olfactory, spatial, and visual. MSB in ants has been repeatedly compared to memory centres of the human brain such as the hippocampus and the cerebellum and certain parts of the cerebrum, a part of the brain associated with learning.
Figure 3: Neurons in the mushroom bodies.
When young ants that had newly emerged from their pupae were allowed to socialize, their MSBs grew in size and volume, while the ants that were socially isolated showed absolutely no changes in these brain areas. This suggests the existence of ‘a critical period of development’. This period of development was observed in younger individuals whose social interactions played a decisive role in their brain development. We see a very period of development in humans, wherein brain development is most stressed upon till early adolescence. With the help of brain imaging, the study succeeded in showing that the ant brains underwent changes when they were deprived of social interactions, offering a window into how brains undergo dynamic changes in conditions of extreme stress like social isolation. Such changes also have physiological manifestations, resulting in behavioural abnormalities.
Behavioural implications of social isolation
In the vertebrates, social isolation can bring about several neurological syndromes like epilepsy, depression, and schizophrenia to name a few. Interestingly, it gives rise to a similar phenomenon in cockroaches–a ‘behavioural syndrome’. A behavioural syndrome is often characterized by a set of traits that are expressed due to certain events or in response to particular conditioning. One study linked the development of a behavioural syndrome in cockroaches to social isolation. The isolated cockroaches became reclusive and risk-avoidant, and researchers co-related such behavioural changes to not having learned ‘social codes’ during the period of development, or to lower metabolism rates arising from living in isolation.
Figure 4: Socially housed cockroaches in a petri dish exhibiting normal behaviours like exploration, communication, and foraging.
In ants, isolation had physiological effects which slowed down their metabolism. The isolated worker ants digested lesser food than the ants that were living together. Ants store food in their crop (Fig. 5) which is an internal organ of food storage. They regurgitate this food in order to feed other ants. A study suggests that mouth-to-mouth feeding in ants which takes place by regurgitation might pass on certain substances from one individual to the other which may be vital to better digestion. The absence of mouth-to-mouth feeding in an isolated ant may have led to less food being sent to the stomach for digestion. Higher mortality rates in isolated ants can even be linked to lesser available energy and increased activity levels (about 10 times higher than usual).
Figure 5: Illustration by Tanvi Gurjar showing social stomach & digestive stomach in ants.
All of the behavioural deviations mentioned so far, also have a profound effect on the amount of sleep an individual gets. Inadequate sleep in vertebrates can negatively impact the ability of brain cells to communicate or can lead to defective functioning by damaging or even killing brain cells. In isolated fruit flies, lousy sleep caused the activation of a stress response called the ‘Unfolded Protein Response’ (UPR). These flies slept less and more discontinuously resulting in higher stress levels, which ultimately induced UPR. UPR, which is beneficial to human bodies because of its role in supporting our immune systems and preventing many detrimental health disorders and diseases, can be extremely harmful if activated permanently, as seen in the isolated flies. Even the long-term activation of this stress response made flies more susceptible to diseases, thereby increasing mortality rates. Similarly, in the vertebrates such as mice, it was shown that long-term social isolation caused increased production of a chemical substance in the brain called Neurokinin B. Socially isolated mice that had elevated levels of Neurokinin B were more aggressive and showed the phenomenon of fear learning which in turn caused scantier sleep. In monkeys, an imbalance of this chemical caused a delay in the onset of puberty. Studies like these are helping science decode ways of early detection and tackling potentially life-threatening conditions by enabling complex studies to be carried out on tameable model organisms like insects.
Studies like these are especially important not only because of their medical significance but also because they help humanize mental afflictions. Understanding the ‘why’ behind our actions helps decrease internalization and self-blame surrounding the issue at hand. Moreover, understanding bodily reactions to stress will also help destigmatize mental illnesses and lessen judgment towards people struggling with them. Such studies help us make sense of the inevitable reality of the health implications of our modern lifestyles, and more importantly, make it easier to endure them.
Perhaps, the next time you feel lonely, you could turn to seek comfort in the company of a bug or an ant and know that even in desolation, you aren’t alone.
Brown, Marishka K et al. “Reduced Sleep During Social Isolation Leads to Cellular Stress and Induction of the Unfolded Protein Response.” Sleep vol. 40,7 (2017): zsx095. doi:10.1093/sleep/zsx095
Seid, Marc A, and Erich Junge. “Social isolation and brain development in the ant Camponotus floridanus.” Die Naturwissenschaften vol. 103,5-6 (2016): 42. doi:10.1007/s00114-016-1364-1
Zelikowsky, Moriel et al. “The Neuropeptide Tac2 Controls a Distributed Brain State Induced by Chronic Social Isolation Stress.” Cell vol. 173,5 (2018): 1265-1279.e19. doi:10.1016/j.cell.2018.03.037
Lihoreau, Mathieu et al. “The weight of the clan: even in insects, social isolation can induce a behavioural syndrome.” Behavioural processes vol. 82,1 (2009): 81-4. doi:10.1016/j.beproc.2009.03.008
Koto, Akiko, et al. “Social Isolation Causes Mortality by Disrupting Energy homeostasis in Ants.” Behavioural Ecology and Sociobiology, vol. 69, no. 4, 2015, pp. 583–91. Crossref, doi:10.1007/s00265-014-1869-6.