The Neuroscience of Loneliness

Humans are built for connection. Humans bargain on social connection not just for social development but for healthy brain development and better physical well being. Now even with it being a fact that we humans need to rely and need social connection for a lot, reports on loneliness are high . For example reports on loneliness have risen since the 2000s and have heightened even more since covid-19. Before covid 20-23 percent of adults reported being lonely and now it seems to be higher (JD Deong) and this seems to pose a problem; especially because loneliness can lead to poor physical and mental health, diminished well being and unable to fulfill societal roles. It is important to  note that loneliness isn't just a psychological thing, it is associated with various health factors such as depressive symptoms, cognitive decline, cardiometabolic disease, and premature morality, which means loneliness can be characterized as a biological stressor( JD Deong). This suggests that deeper things happen when loneliness occurs. It is also important to note that loneliness and social isolation isn't entirely the same thing : although feeling lonely can cause you to socially isolate yourself because you feel as though your social needs are not being made and making connections with people feeling unfulfilling,  a person who socially isolates herself and has maybe 1-2 friends by his or her side   can feel content; rather, a person who has loneliness can feel not so content even though they may have 10 friends by their side because they feel that their social needs are not being met  and  they can feel like the odd one out, ultimately this means they be in their head a lot, so it is important to acknowledge all the deeper neuro networks and systems that goes on with these people that experience loneliness.

People who experience loneliness are in the head a lot since they feel like their social needs are not being met and this causes them to be more in  touch with their DMN ( Default Mode Network) (JD Deong). For example, there was a study done that  had 40,000 adults link a self report measure of perceived loneliness to multimodal MRI revealed the strongest associations in the DMN (JD Deong). In lonely participants, there is a more gray matter value and strongest functional connectivity between the DMN hubs ( medial prefrontal cortex,posterior cingulate cortex , one assumption for this is that since their social needs are not being met (JD Deong). Their brain relies  more on internal stimulations- memories, imagined interaction-etc to fulfill them.

Another effect that loneliness has on the brain is the effect on the HPA axis. The Hpa axis is a neuroendocrine system that regulates stress responses, energy balance, and hormone production through a feedback loop involving the hypothalamus, pituitary gland, and adrenal glands ; what loneliness does to it is that it makes it unregulated: and with it being unregulated it results in hypersensitivity to minor stressors which is cortisol, and when there is high cortisol levels it equals to chronic stress and more stress making loneliness be a biological stressor because it takes such a toll on our brain systems and make us develop chronic stress In addition to loneliness making us having chronic stress. There are things called Glucocorticoids which are steroid hormones that regulate metabolism, suppress inflammation, modulate immune responses, and help the body respond to stress ( Carmen Pope).If there are individuals are chronically over exposed to glucocorticoids chromosomes secreted from the adrenal glands, and effectors of the HPA axis, their neurons become less plastic in neuronal regions high in glucocorticoids receptor ( hippocampus) ( JD Deong). This decrease in neuroplasticity has been shown  to lead to difficulties staying positive, poor emotional regulation, and difficulties with memory.  In addition the immune system also changes when experiencing loneliness. Low grade systemic inflammation is often present which can be associated with inflammatory biomarkers molecules that can be measured in blood that reflect immune activity- the reactive protein ( app) and interleukin 6( Il-6e) (JD Deong).

These immune changes converge with Hpa dysregulation to provide changes in the brain-cytokines and glucocorticoids circulating in the blood with influence neural plasticity and glial activity  in stress sensitive neural networks (JD Deong).This gives the main mechanism for outcomes like increase threat vigilance and social anhedonia (not being able to enjoy activities  that are normally rewarding).  This shows that loneliness has some deep effect on the brain because it increases the threat for connection which makes individuals not to make social connections because they are scared and not find joy in it any more. In addition to it having a deep effect on the brain because it increases the thoughts that social connection is scary and that thought process would likely make an individual not want to make social connections, it as we know decreases neural plasticity and that is very important characteristic to the brain, so if it can decrease that it is a  guarantee it will lead to big problems because neuroplasticity is a vital  to the brain networks and systems , this further proves that loneliness  do have have major effects on people neuro-wise and it is deeper than a physiological strain and is a biological stressor and make it hard for people to socially adapt to a new place.

We all know that feeling lonely can eventually lead social isolation, but if it leads to that it makes it hard for an individual to socially adapt to a place, therefore likely making the feel more out of place because they don't know the community or their societal roles and this increases loneliness because now you feel like you don't belong.

Additionally, less social interactions restricts the advantages of social adaption like lacking social support; then lacking it is bad because with that social support you can better adjust to a community and feel comfortable, but if you don't  have that social support it does make you feel lonely and leads to that social isolation because of loneliness. Since feeling lonely leads to  loneliness and does indeed have deeper effects on the brain, it has been shown to have to have a positive correlation with abnormal functional connectivity  (FC)  of alteration (dorsal and (ventral networks) and control networks ((Cingulo-opercular network and right middle/superior frontal gyrus)  ( Daniel Franco-O’Byrne et al). These alterations to these connectivity networks are known to strengthen maladaptive characteristics of loneliness such as  social affiliation,reducing likeliness to be with other people , negatively based cognition, emotion dysregulation , high social pain, and impaired social cognition w(a reduced ability to understand, interpret, and respond to social information) (Daniel Franco-O’Byrne) . 

Although loneliness has been shown to alter these connectivity networks in the brain in a negative way, social networks have been proven to alter it back and do seem to  help social adaption. For instance,  social networks provide support through emotional, instrumental, and  informational resources that facilitate social adjustment and coping ability while reducing stress. Also at the neurocognitive level, these stress-lessening effects are also regulated by pre-frontal activation and fronto-limbic connectional connectivity, which essentially means your emotions (limbic) is talking to your brain (fronto), associated with adequate cognitive function, self regulation and social cognition, you will now have the ability to think straight and understand the conversation and know how other people are feeling. To prove the extent social networks have on social adaptation essential to decreasing loneliness, scientists did an experiment  and their experiment showed regression that loneliness was associated with low scores on the social adaptation scale (Daniel Franco-O’Byrne et al). The model also showed that the effect of loneliness on social adaptation decreased after including social networks (Daniel Franco-O’Byrne et al ). One of the important networks that the model showed that decreases with loneliness is decreased connectivity of the amygdala .  Past research shows the amygdala is important for modulating emotions  regulation and also affects social perception;  if there is poor front-amygladar connectivity ,it might indicate poor social cognition regulation impairment and poor mental health. This also illustrates what the deeper effect loneliness has on the brain and how one of the big things is emotional dysregulation and that loneliness should try to be prevented or social networks should be implemented to decrease. In addition to social networks helping to decrease networks, oxytocin  modulates emotional regulation by increasing amygdala and prefrontal connectivity. Additionally, regarding social connectivity, oxytocin has been shown to weaken negative bias within regions involved in the theory of mind (temporoparietal junction) and identification of emotional cues in social perception (right fusiform) (Daniel Franco-O’Byrne et al ).  This might illustrate another thing that can be implemented to reduce loneliness, however more research should be done because the relationship between oxytocin and social adaptation and loneliness is merely speculative.  

Lastly, there are  other solutions in addition to social networks and perhaps oxytocin, more practical ones like reintroducing community to a person experiencing loneliness.For example scientists did an experiment where mice went 4 weeks of isolation there was reduced BDNF, a protein necessary for neuron growth and synaptic plasticity (JD Deong). Also isolation also showed impaired hippocampal function and dendrite function( mostly due to decreased plasticity in the brain), but when the mice returned to social enriched environments for four weeks and everything was  restored, every network and every thing that was dysregulated went back to normal (JD Deong). This means that social enrichment can effectively reverse neural deficits caused by isolation.With that said, intervention of cognitive behavioral strategies  that target maladaptive social cognitions such as negative bias and teaching social skills are way more effective than those who contact them with more people. If loneliness exaggerates a negative bias towards connection and enforces self protection, we can train our brains to think positively about interactions and dampen the potential threat and regulate the salience, amygdala  neural network ( regulates emotions and if active it causes dysregulation emotions) rather than activate it. Also having system level interactions like sending loneliness-impacted people to community volunteer programs and befriending programs. This can make supportive engagement and it can increase their  sleep, mood and decrease stress levels, ultimately retrain the front-limbic circulatory system, restoring emotional regulation and reducing the hyperventilation stress responses associated with loneliness. Also, we still don't know know whether loneliness causes all these things or if there is a pre existing thing that pertain to loneliness, but we can infer a bi directional is likely involved: perceived loneliness leads to hypervaporation stress and hypervigilant nuances which exacerbates the loneliness and the cycle just continues.

In conclusion, loneliness is a big thing that can affect deep things in our brain and alter our brain networks altering how it functions, which is why it can't just be characterized as physiological restraint , it is biological stressor because by altering how our brain function it can lead to serious effects like dysregulated emotions and chronic stress. We still don't know how loneliness is specifically called but we can infer it just starts by feeling lonely leading to stress and potential threat to a communication and then when a conversation goes wrong because of that the isolation and negative bias cognition to social adaption//connection, the cycle continues, but with certain  social networks those effects can be reduced, being in a more social enriched environment can decrease them and doing a cognitive targeted therapy  can retrain your brain to think positively about interacting with people and lastly just being a friendly community can really help loneliness-impacted stress be reduced and its negative cognitive reaction to making connections with other people can be flipped to positive and its emotions be calm and collected.

Franco-O’Byrne, D., Sepúlveda, J.P.M., Gonzalez-Gomez, R. et al. The neurocognitive impact of loneliness and social networks on social adaptation. Sci Rep 13, 12048 (2023). https://doi.org/10.1038/s41598-023-38244-0 

Neuroscience of Loneliness: How Social Isolation Reshapes the Brain — GreyMattersTU 

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