10 September 2026, by Anna Priebe

Photo: AdobeStock/dule964

An electroencephalogram is used to visualize the electrical signals generated by brain activity.

The electroencephalogram, or EEG for short, visualizes electrical activity in the brain and is an important research tool. But what can it reveal about a person’s personality? Prof. Dr. Jan Wacker and Dr. Katharina Paul from the Faculty of Psychology and Human Movement Science are working on this topic as part of a large collaborative project and are also focusing on the research method itself.

Can you explain briefly what an EEG is and what it is typically used to examine?

Wacker: When we think and perceive, electrical activity occurs in the brain. Using electrodes placed on the scalp, we can measure this activity on the surface of the skull. Each electrode sends a signal that is recorded and compared to the signals from the other electrodes. We refer to these recordings as an electroencephalogram, or EEG.

The EEG has a wide range of applications; for example, in medicine, it can be used to diagnose epilepsy. In psychology, it is primarily cognitive processes that are examined. We are particularly interested in changes in brain activity over a specific period of time. With the EEG, we can see when certain areas of the brain are activated—for example, in response to a stimulus or when solving a task.

You’re investigating to what extent EEG results can also provide insights into personality traits. Can you give an example?

Wacker: We’re interested in the individual differences in these EEG signals. We can already observe these differences when participants sit down completely at rest, because depending on their personality, they spontaneously think differently in this situation. Some are relaxed, others are brooding—and their brain activity differs accordingly.

But it’s even more exciting for us to examine this under specifically selected conditions—that is, to give participants certain tasks and study their brain responses. One hypothesis, for example, is that in more anxious, brooding individuals, certain regions of the brain are activated more strongly when they realize they’ve just made a mistake. This is referred to as error-related negativity.

Is the goal here to draw conclusions about personality from an EEG later on, or rather to better contextualize the findings?

Paul: Basically, our research always makes statements about groups and not about individual people. Our goal is to learn more about the processes in the brain, and the EEG provides us with clues as to how these processes might differ in people with anxiety. This allows us to gain a better understanding of this personality construct.

You collaborated with a total of nine German universities on this project. What is the advantage of such a large-scale collaboration?

Paul: First of all, it’s always more fun to work on things together, of course. But above all, this research topic presents us with unique methodological challenges. That’s because these reactions involve tiny signals in the brain that are constantly masked by so-called “noise” in the EEG. To reliably detect such small effects—and, above all, statistically significant differences—we need a large number of participants. Not ten or 20 people, but hundreds, if not thousands. That wouldn’t be feasible at a single location, which is why we’re collaborating.

We had about ten times more participants than in other studies of this kind

So you’re pooling your participants to investigate the various research questions?

Paul: Ten labs also mean ten different research focuses. Some work on anxiety and error processing; we focus on rewards and their effects when comparing introverted and extroverted people. So when we test our participants, we also give them tasks from the other nine areas—and they include ours in their tests. This gives us a particularly large dataset and allows us to answer a wide range of questions.

Wacker: In our project, we had about ten times as many participants than in other studies of this kind. Based on this, over the past seven years we’ve examined many different effects that had previously been observed repeatedly in smaller studies. So far, none of these effects has been conclusively replicated in our much more extensive study. So they are by no means as stable or as significant as one might have assumed ten years ago.

What does this mean for psychological research?

Wacker: On the one hand, it means that much larger sample sizes are needed to make valid statements about the influences of personality traits. And second, that researchers must consider how they will analyze the data before conducting the study. This is a key finding from the project: There are millions of ways to perform a statistical analysis based on the EEG waveforms that have been measured. And the methods sometimes yield very different results. We therefore conclude from our project that it is absolutely necessary to always pre-register this type of research.

What exactly does that mean?

Wacker: It means you have to specify in advance exactly how you’ll handle the data you’re going to collect. So far, this has only been done in about five percent of the studies that use EEG results to investigate correlations with personality traits. In the other studies, it cannot be ruled out that various analysis approaches were tried out and that, in the end, the researchers reported what “worked.” In any case, this could explain why most studies—even those with only a few participants—find correlations that cannot be confirmed later on.

As part of the project, we held workshops before the start of the study to determine which analysis method we would choose for each research question and which alternative approaches would also be justified. In the first round, we tested nearly 2,000 such alternative analysis approaches on each individual research question. The resulting range of results for individual effects shows just how significant the influence of the chosen method is.

So researchers need to be more aware of this?

Paul: Yes, because it’s always important to reflect on one’s own research and one’s own role—for example, when deciding for or against a method. Incidentally, this applies not only to the use and analysis of EEG but to all methods, ranging from functional magnetic resonance imaging and other biological measures to behavioral observation and the analysis of questionnaire data. Here, too, there is always some leeway in the analysis that must be minimized through appropriate processes in the research design. This may be particularly noticeable in research questions that examine individual differences between personalities, since the effects we’re interested in are so small. But fundamentally, the same limitation applies to every study. That’s what makes our project universal.

(This content has been translated automatically.)