We recently talked to Zlatan Krizan about his paper, "Personality and sleep: Neuroticism and conscientiousness predict behaviorally-recorded sleep years later", which will appear in an upcoming issue of EJP. Zlatan is a professor of psychology at the Iowa State University.
Read more about the study below!
Q: Hi there Zlatan! Can you tell us a little about yourself and what got you into personality psychology?
I’m originally from Croatia, and I came to the United States as an exchange student. I took a seminar on memory illusions when I was an undergraduate student, in which I helped design an experiment -- it really got me hooked on psychology. Then, I enrolled in a social and personality psychology doctoral program at the University of Iowa, where I worked with Jerry Suls, Robert S. Baron and Paul Windschitl, and also took courses from David Watson. At some point, I became interested in individual differences in implicit and explicit self-esteem,. and then in other aspects of self-evaluation as well.
I have been involved in a lot of different research domains to see where I should invest my efforts for the next phase of my career. I think sleep is very interesting, because it’s such an essential, basic function that we all partake in. As such, I was really shocked that there was almost no literature on sleep and social processes or on sleep and personality. I thought that such a fundamental process must have really important implications for how we regulate our emotions, how we interact with others, and who we become in the end, from a personality perspective. That’s what got me interested in studying this domain. I wanted to know what exactly sleep can tell us about personality and what the mechanisms are -- both short-term and long-term -- that may explain these dependencies. I think that this is a useful direction in research, because sleep is something that is very flexible and modifiable. So that makes it very open to intervention, but it can also lead to some insights about how individual differences are connected to basic biological processes in ways that are different than looking at, for example, brain functioning.
Q: What is your study about?
A few years back, I really became interested in how sleep intersects with social processes and personality differences. And looking at what we knew about the links between sleep and personality, did not reveal very much. The literature mostly addressed subjective sleep quality or self-reports of sleep. To the extent that objective sleep measures were actually taken, they usually always were linked to specific mental illness diagnoses, such as anxiety and depression. Particularly with regards to personality, one couldn’t get a clear picture of what personality traits tell us about how people sleep. I was interested in what personality means for how long you sleep, how continuous your sleep is, and how stable your sleep day to day is. We just didn’t have good answers to these questions before this study. So these things were really the inspiration of this study.
In this study, we used data from the Biomarker project of the Midlife in the United States Study (MIDSU) that included 382 participants. In this project, participants underwent a week-long examination in which their sleep was behaviorally measured via wrist-worn accelerometer technology that infers sleep and wake based on bodily movement. These behavioral measures, as well as subjective sleep quality, were tracked across seven days, while personality traits were measured several years prior to that. So, this was a great opportunity to test to what extent the different personality domains foreshadow specific aspects of sleep – and not just self-reported sleep. In addition, we were also able to look at how much sleep varies across days, rather than just how somebody typically sleeps .
The main finding of this study was that personality traits are pretty substantive predictors of future sleep behavior. In particular, we found that traits like conscientiousness and neuroticism don’t just foreshadow self-reports of better sleep, but that personality is also reflected in sleep continuity (i.e., amount of interruptions during the night). Even more interestingly, we found that conscientiousness and neuroticism were related to more and less day-to-day sleep variability, respectively. I think that is important, because it suggests that the variation in sleep from one day to the next could hold important clues for example for emotional variability, which is at the core of neuroticism, or, why individuals may give in to their impulses, if they are low on conscientiousness.
Q: What do you think are important implications of your study?
I think it was very interesting that neuroticism – or any of the traits – did not predict how long people sleep typically. More neurotic or less neurotic people did not necessarily differ on how much sleep they get on average, but they had more variation from this average across days. This tells you something important. Specifically, it tells you that one day this person is going to be sleep deprived and is likely to be frustrated, then will make up for that sleep the next day and might be less so. So, you will have this instability in reactions which really cuts to the core of the construct. It’s just one thing that can help explain why neurotic individuals are more unstable. Part of the answer may be that their sleep is also unstable. If your sleep is unstable, it’s hard to be behaviorally stable.
I think it is also important to note the possibility for bidirectional relationships between these two constructs. In some analyses that we are doing right now it seems that sleep can play a more formative role in personality development. There is similar evidence from studies that have tied temperament to sleep in children, such that toddlers who got good sleep actually showed more optimal personality development later on. For instance, children that sleep better may actually have lower neuroticism in later years. The implication here is that how we sleep may impact the development of traits such as conscientiousness and neuroticism. Conversely, we found in the present study that personality may set important patterns of sleep that then remain for many years to come. Also, I think it’s important to take the timespan into account – some of these processes may unfold very quickly whereas others may unfold over a longer time span. For instance, someone who feels more tired on a particular day because they have had less sleep that night might make up for it by sleeping more the next night, causing that person to return to baseline. However, being chronically underslept for years may alter brain and behavioral functioning as to contribute to more durable personality differences.
Q: Where do you see yourself in the (near) future?
Really digging in to examining which traits matter for which aspects of sleep and why. We are now still at a very general level of understanding. That is, we know that domains of personality, especially neuroticism and conscientiousness, are important for sleep continuity and regularity. But what we don’t know for example is to what extent differences in sleep architecture – so the different stages of sleep, such as REM where we dream versus non-REM where the body and brain are generally deactivated – may further reflect something about personality. We are currently planning a study in which individuals will undergo at-home electroencephalography (EEG), which can then directly measure sleep duration as well as different stages of sleep, and then connect that to self-reports and peer-reports of normal and abnormal personality differences. For example, REM sleep has been implicated in emotion regulation and problems with extinction of traumatic memories and associations. We really don’t know, but one possibility is that neurotic individuals could have more REM sleep, which is for instance observed in clinical depression. So, the next step is to see whether some of these suggested patterns that we’ve seen in clinical science and neuroscience will actually hold when examining personality directly.
In addition to looking at these links more in-depth, in a study that we are just writing up on data from the Minnesota Twin Study of Aging and Development with approximately 675 monozygotic and dizygotic twins, we are using quantitative genetics to look at whether there are shared genetic bases between reports of sleep and personality. We know that there is an overlap between neuroticism and poor self-reported sleep quality, and we know that there are genetic components to personality as well as sleep patterns, although the latter are a bit weaker. Now the question we are looking at is whether there are common genetic influences between subjective sleep quality and personality.
Q: Do you have any tips or advice for young researchers?
That’s a great question. I think that the first tip is to study something that has real-world implications. There’s a lot of interesting phenomena to understand and often as academics we have the luxury to focus on things that we find interesting. Of course, a lot of time that’s driven by forces we don’t understand – I don’t know if you’ve heard the saying “all research is me-search”? Of course, you have to be passionate about what you study, but you need to avoid getting lost in interests or whims of the moment. What we study should be something that is important in the real world, something that involves problems that people have, and something that can occupy you for a long time.
I remember one time going to my advisor in graduate school about the possibility of writing a paper on a particular topic and asked him whether it was interesting. And he asked, “It is interesting. But is it important?” I think that is the question we need to regularly ask ourselves.
And, I would say to just keep at it, and try to develop a research profile. If you’re studying something important, there’s going to be people around who, from different fields or for different reasons, are dealing with the same topic. So that again allows you to develop a scholarly profile that may serve you better than having a general training in an isolated field, even if that training is excellent.
In any field, we may sometimes get insular. For instance, you develop a certain language, a certain way to study things, certain assumptions about how things work, and it can be tough to get out of those. I was always engaged in both social and personality psychological research, which were sometimes at odds in the history of the field, but I think most people recognize that they are often two sides of the coin that are both critical, especially if we want to get the full picture of human nature.