Lonely or Hungry – Can your brain tell?

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Due to the COVID-19 outbreak, the year 2020 has presented us with largely unexpected situations.  Our lives changed drastically, almost overnight. We have all, inevitably, been subject to the myriad of COVID-19 restrictions and for many, the social isolation aspect has hit them the hardest. It must be said, however, that social isolation is not a new concept, or a concept solely associated with lockdown restrictions following the pandemic. In fact, it has been under review, and a topic for research for much longer.

In a new study published in the Nature Neuroscience magazine; researchers report to have been collecting data about the effects of social isolation in the brain since 2018! Not only were the researchers interested in the effects of social isolation on the brain, but they wanted to compare these effects to what they thought would trigger a rather familiar, in some ways, similar sensation: hunger cravings.

When we “crave” social interaction, could this be the same sensation we feel when craving food?

To test this, the researchers created an isolation environment where they confined 40 participants. They spent 10 hours in a room with no windows and could not use their phones. There was a computer in the room, that they could use only to contact the researchers if need be. To achieve social isolation, the corridors would be emptied when the participants used the bathroom. Food was delivered to their door but was only available to them when the deliverer had evacuated.

The participants, at the end of the research were required to perform an MRI scan. Prior to the isolation period, the participants had been taught how to operate the machinery in order to remain in isolation until after the scanning.

On a different day, the same participants were put under a 10-hour fast period followed by another MRI scan. During the scans following the isolation and fast periods, the participants were shown images of food, images of people interaction and neutral images (e.g. flowers).

The researchers were particularly interested in the activity of the substantia nigra – a tiny structure in the midbrain, previously linked to hunger and drug cravings. This structure is also thought to share evolutionary origins with a brain region in mice called the dorsal raphe nucleus – an area found to be active following social isolation in a 2016 study.

a cross-section of the brainstem showing the two substantia nigrae.
A cross-section of the brainstem showing the substantia nigrae.

Therefore, it was expected that when socially isolated individuals saw photos of social interaction, they would send a “craving signal” in the substantia nigra similar to the signal produced when they saw pictures of food after fasting. That is exactly what they saw! Additionally, they were able to associate the activity in the substantia nigra with how strongly the participants rated their craving for social interaction or food.

Another interesting finding is that people’s responses to isolation depended on their usual level of loneliness. Those who indicated feeling chronically isolated before the study showed weaker craving for social interaction than people who reported an active social life.

The MRI also reported activation in other parts of the brain: the striatum and the cortex. However, hunger and isolation activated different areas within these regions. Suggesting that these areas are associated with more specific types of crave compared to the substantia nigra whose activity indicates a general feeling of craving.

These findings give us some insight on how different types of people experience social isolation and how these are represented in our brains. The researchers ponder whether these findings could be used to predict how the same participants responded to the lockdowns during the COVID-19 pandemic.

How are you navigating these feelings of social isolation?

Original Source: Tomova, L. et al., 2020. Acute social isolation evokes midbrain craving responses similar to hunger. Nature Neuroscience, 23(12), pp.1597–1605.

Link: https://www.nature.com/articles/s41593-020-00742-z

Featured photo by Burst from Pexels

Edited by Malavika Ramanand

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