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Individual Differences in the Brain: Neuroticism

In the first post of this series, we discussed Eysenck’s Big Three personality theory from the biological perspective. His theory stated that there are individual differences in the brain, which can be linked to three personality dimensions, namely extraversionneuroticism, and psychoticism. In the previous post, we focused on the individual differences regarding extraversion. Today, we will focus on neuroticism.

Eysenck’s Big Three: Neuroticism

Eysenck described this dimension as a continuum, ranging from “neuroticism” to “emotional stability”. In his dimension, individuals with higher levels of neuroticism are characterized by experiencing more negative affect (such as anxiety, worry, envy and frustration), less emotional stability, and lower tolerance for stress and aversive stimuli. Individuals with lower levels of neuroticism on the other hand, are described as less prone to experiencing negative affect, being more emotionally stable and having a higher tolerance for stress and aversive stimuli.

The neurotic vs. emotional stable brain

How did Eysenck predict “neurotic brains” to differ from “emotional stable brains”? Well, he expected to find individual differences in the level of activity of the limbic system. This system is the part of the brain that is involved in the processing of emotion, motivation, pleasure and emotional memory. As this system is mostly involved in emotional processes, Eysenck hypothesized particularly that we can find individual differences in the brain when individuals are faced with emotional stimuli.

Also, because Eysenck defined neuroticism as characterized by more negative affect, he predicted “neurotic brains” to be more predisposed towards negative emotions. Where he expected individuals with higher levels of extraversion to show more activity in the limbic system when faced with positive emotional stimuli, Eysenck expected individuals with higher levels of neuroticism to show more activity when faced with negative emotional stimuli.

Thus, simply put, Eysenck predicted individuals with higher levels of neuroticism to react stronger to emotionally arousing stimuli on the neurological level, and especially pay greater attention to negative emotions. Validating Eysenck’s hypotheses regarding neuroticism should be possible by examining the level of activity in the limbic system when individuals are faced with emotional stimuli.

Was Eysenck right regarding neuroticism?

Now the only question that remains is; are Eysenck’s predictions correct? Overall, the answer seems to be yes. During the last years, studies have shown that greater neural activity in the limbic system to positive emotional stimuli is indeed associated with higher extraversion, whereas greater neural activity to negative emotional stimuli is associated with higher neuroticism. It has even been shown that the level of neuroticism influences activity in the brain before a negative emotion stimuli is visible; simply the anticipation of a negative emotional cue can be enough to trigger activity in the “neurotic brain”. This supports the idea that individual with higher levels of neuroticism are more sensitive to negative emotions, and pay more attention to them.

Another important finding comes from one of the structures within the limbic system that is often studied, namely the amygdala. This part of the brain is involved in memory, emotional responses (particularly fear, anxiety and aggression) and decision-making. Studies linking amygdala activity to neuroticism have shown that individuals with higher levels of neuroticism show increased reactivity in the amygdala to emotionally arousing experiences – not only do these individuals react more strongly to emotionally arousing experiences, they also take longer to return to pre-arousal states. The latter might explain why it can be so difficult for neurotic individuals to “let go” of their negative mood or their worries; because they are more fixated on negative elements, and their amygdala needs more time to recover. This might also be part of the explanation why individuals with higher levels of neuroticism tend to be more vulnerable for depressions.

Future research

Because negative affect plays a central role in neuroticism research, most studies so far have focused on reactions to negative emotional stimuli and regulating negative emotions, rather than purely cognitive paradigms when examining brain activity. That it might be interesting to also invest more effort in purely cognitive paradigm studies, has been shown by Robinson and Tamir in 2005, who found that individuals with higher levels of neuroticism showed greater trial-to-trial variability in cognitive performances as compared to individuals with lower levels of neuroticism. This means that individuals with higher levels of neuroticism fluctuated more in their response time to tasks, which in turn may reflect task-irrelevant cognitions such as preoccupations and worries about performance.

Beside this line of research, there are other perspectives and methodologies that are interesting as well. For instance, there are also connectivity studies; studies that focus on the interaction of several brain structures and investigate the brain as a “network” of actions and activity. These have shown that individuals with higher levels of neuroticism, as compared to individuals with lower levels of neuroticism, may exhibit a brain network that is less functional and structured more randomly. Why this is the case, what the consequences precisely are, and whether this pattern is generalizable to all “neurotic brains” or only a specific subgroup, is not certain yet – but it is definitely worth exploring.

A lot of information! What did you find most interesting about this topic, and if it were up to you, what kind of research would you like to conduct here? Is there more that you would like to know? Let us know by leaving a comment below!

If you are interested in reading the literature used for this post, references and links are provided here:

Eysenck, H. (2006). The Biological Basis of Personality. New York: Routledge.

Mitchell, R. L., & Kumari, V. (2016). Hans Eysenck’s interface between the brain and personality: Modern evidence on the cognitive neuroscience of personality. Personality and Individual Differences103, 74-81.

Robinson, M. D., & Tamir, M. (2005). Neuroticism as mental noise: A relation between neuroticism and reaction time standard deviations. Journal of Personality and Social
Psychology, 89, 107–114.

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