Could Your Immune System Be Making You Impulsive?

By Emma Young

You can have £10 today or £12 next week. Which do you go for? 

Being able to forego a reward now in favour of gaining something better later is known to be important in determining all kinds of desirable outcomes in life, including greater educational attainment, social functioning and health. 

However, choosing to delay gratification won’t always be the best option. If you’re in desperate circumstances – you badly need money to buy food, for example – taking the £10 today could be sensible. But this isn’t necessarily an entirely conscious judgment – there may be biological systems that automatically shift your decision-making priorities according to what is most likely to enhance your survival. A new open-access study published in Scientific Reports provides evidence that having raised levels of inflammation in your body, which is generally caused by the immune system’s response to infection or injury, can skew your judgment to focus more on present rewards, and on instant gratification. If further research backs this up, there could be wide-ranging implications not only for understanding why some people are more impulsive than others, but even for treating substance abuse. 

Jeffrey Gassen and colleagues at the Texas Christian University, US, reasoned that inflammation should enhance a person’s desire for immediately available resources, as the body’s response to sickness requires extra energy, and, for a sick person, their future is less certain. To explore whether this is actually the case, they recruited 159 healthy, non-obese, young college students who abstained from behaviours that can cause an acute increase in inflammation, such as smoking, exercise, sex and drinking alcohol, for two days prior to the study. 

The participants completed a widely-used impulsiveness scale, an instant gratification inventory, as well as two behavioural assessments – one of which explored their preferences for smaller and immediate vs. larger, delayed rewards. The participants also reported their body mass index, physical activity levels, smoking, alcohol consumption, sleep quality, stress and other variables (all of which relate to having a greater focus on the present, to inflammation levels, or both). 

The participants then gave blood samples, which were checked for levels of three pro-inflammatory cytokines (proteins that indicate greater inflammation). The researchers found that participants with higher levels of inflammation also tended to have a style of decision-making characterised by impulsivity, a focus on the present, and an inability to delay gratification. 

This analysis alone of course cannot indicate the direction of the relationship. Might it rather be the case that harmful, present-focused behaviours were driving higher levels of inflammation? The researchers explored this possibility by looking to see whether particular behaviours – usual levels of smoking, alcohol intake and risky sexual behaviours, for instance – predicted greater inflammation. But none did. 

This might sound surprising (as smoking, for example, has been clearly associated with inflammation in past studies). But these participants were chosen on purpose to be healthy and young. They were also instructed to avoid such behaviours for 48 hours prior to the study, in theory to make it easier to isolate any effects of inflammation on decision-making. 

All in all, “these results suggest that the activities of the immune system may play an important role in shaping decision-making preferences,” Gassen and his colleagues write. In doing so, they add “…to the growing body of research demonstrating that the internal, physiological condition of the body plays an important role in modulating decision-making and behaviour.”

If further experimental work can firm up this link, there could be “exciting new possibilities” for treating substance abuse disorders, the researchers suggest, and there could be implications for people who have experienced early life stress, who are known to be more prone to inflammation. Drug-based or behavioural interventions targeted at reducing circulating levels of pro-inflammatory cytokines might possibly “sever the link between an individual’s propensity to inflammation and undesirable behaviours, improving outcomes for those from disadvantaged backgrounds.” 

As the researchers themselves point out, clearly a lot more work has to be done. But as they also note, this study was on healthy young people, with relatively low levels of inflammation. People with chronic illness or obesity have persistently high levels and the activity of their immune system may then have an even greater effect on the way that they behave and even think. 

Inflammation Predicts Decision-Making Characterized by Impulsivity, Present Focus, and an Inability to Delay Gratification

Emma Young (@EmmaELYoung) is Staff Writer at BPS Research Digest

8 thoughts on “Could Your Immune System Be Making You Impulsive?”

  1. You may have left room for a little philosophy…
    …are we becoming more aware of ourselves, as interacting independent living systems of Being; thanks…

  2. Lots of research has demonstrated that psychological stress influence inflammation (i.e., this is the direction of causation). Psychological stress also can influence impulsivity (for example, stress reduction techniques such has mindfulness practices lower both stress and impulsivity) – this would explain the results of this study.

  3. The delayed choice tests are thoroughly flawed for the following reasons:

    The assumption is that the only variables are the delay and the amount of money but this is not true.

    To receive the reward later one has to make arrangements, must remember to collect (scheduling issues and other hassles) and there is, especially for young people, the looming experience of people borrowing money with the promise of returning it ‘later’, which is always very annoying.

    This baggage is brought to the delay option and so the individual weighs the small increase in reward, even up to double the amount, with the hassle typically associated with monies owing and may find that taking the money now and avoiding that hassle is the best option, especially if experience with parental promise of monies that never materialise is still fresh in the mind and lurking as a subconscious bias toward immediacy of reward.

    To control for those variables the two delays should both include the said hassles, that is, to have the money in two days or two weeks. This will control for the hassle property and in my estimation greatly reduce the difference between the two options. If the choice is between two weeks and a month there will be an overwhelming bias toward the larger amount and longer wait as the hassle element is completely controlled for.

  4. In The Broken Ladder, Keith Payne looks at inequality, specifically the stress related to it and the results that follow from it. High inequality appears to mimic poverty, even for those who aren’t poor. It makes people feel stressed out. They increasingly fall into short-term thinking and impulsive behavior (and other things such as more likely to hold irrational beliefs).

    There is a close link between inflammation and stress. Inflammation stresses the body and mind, and with enough inflammation causing one to feel stressed. In the opposite direction, stress from any source can potentially cause inflammation. High inequality is one such stressor.

    Many physical and psychiatric illnesses are found at higher rates in high inequality societies. I bet the same thing would be true for inflammation as well.

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