Dear study participant

Shortly before the turn of the year, we would like to once again use this newsletter to inform you about the progress and results of the Bavarian Longitudinal Study. Since June of last year, we have been conducting the sixth phase of the study (called BEST6@38). We would like to sincerely thank you for your commitment. It is truly wonderful to repeatedly witness your willingness to participate. This is by no means something to be taken for granted, but something very special. Remaining loyal to a study for decades is an extraordinary achievement. Your loyalty has helped the Bavarian Longitudinal Study gain global recognition. Numerous new findings have emerged that now help to better support the development of the next generations.

Participant Numbers and Achievements: A Look at the Last 18 Months

Eighteen months after the start of the new study phase, we have been able to contact 380 participants; more than 310 have already completed the telephone interview, and over 220 have attended the assessments in Munich. Nearly 280 saliva samples have been collected and analysed. Thank you for taking the time and effort to do this. The shipping process, in which the sample is only marked with a number and sent in an envelope without a return address, ensures that you remain anonymous.

New options for participation: Home visits and flexible contact times

Unfortunately, some participants have told us they no longer wish to participate. We deeply regret this, because the success of long-term studies (and we now have 38 years behind us) depends on consistently high participation rates. Of course, we understand that participation may not be possible right now, but things may look different in a next phase. Many of you are currently in the childcare phase. During this time, it can often feel like you don’t know where your head is at, and it doesn’t help that access to childcare does not seem to be getting any easier. Therefore, we would also like to call you in the evenings or on Saturday mornings, because many of you work and should not be contacted during regular working hours. Sometimes coming to Munich for the assessments is also not possible. For this reason, we now offer home visits. Our initial experiences have been very positive, and we hope that this option will be helpful whenever traveling to Munich is not feasible.

Introducing Our Team: Additional Support for the Study

In our last newsletter, we introduced the teams in Bonn, Munich, and Warwick. You can also of course find them on our website. Because contacting participants and arranging appointments can be time intensive, our team in Bonn is now being supported by three students: Hannah Busch, Helena Freiberg, and Oumie Sanyang will be contacting you together with the team members you already know. In Munich, Rebecca Hippen has been doing an outstanding job planning and organizing all assessments conducted on site. All four new team members have been a tremendous help.

Invitation to our summer party: Celebrate with us in Munich!

There are more news: On September 6th, 2025, starting at 4:00 pm, we would like to invite all participants to a summer party in Munich. Please save the date, additional details will follow next year. We look forward to meeting you in person, and this event will also offer an opportunity to meet the other participants.

As in previous years, we would like to present the findings of the study:

1. Changes in Social Relationships with parents, partners, and peers between 26 and 34 years of age

Good social relationships are essential for well-being and a healthy, fulfilling life. A study using data from the Bavarian Longitudinal Study (BEST) showed that adults who were born very preterm (before the 32nd week of pregnancy; VPT) or with very low birth weight (under 1500 g; VLBW) can develop social relationships as close as those of full-term adults, but this is often more difficult and challenging for them. They have friends, are in partnerships, and can rely on stable bonds - even if on average they are slightly  more shy adults born at term. To better understand how relationships with parents, partners, and peers develop into the thirties, we analysed study data from VPT/VLBW adults and full-term adults aged 26 to 34.

Stable relationships with parents

The Bavarian Longitudinal Study found that adults born very preterm have just as close relationships with their parents just as those born at term. In fact, men born at term had the worst relationships with their parents in their mid-thirties. The majority of very preterm adults experienced their relationship as similar to that of their full-term peers.

Same quality of friendships

There is a difference between adults born very preterm and those born at term when it comes to romantic and peer relationships between ages 26 and 34. This is mainly because preterm adults more often report difficulties forming new relationships.  This includes going out, approaching new people and initiating contact with a potential partner. Despite these differences in the twenties and thirties, both groups — preterm and full-term — showed the same improvements in partner and friendship relationships from age 26 to 34. When preterm adults do have friendships or romantic relationships, the quality of these relationships is the same.

Important findings

The results suggest that parent-child relationships in adults born preterm are resilient — despite an often difficult start in life and early separation due to neonatal intensive care. This is reassuring, as many scientists had feared long-term difficulties, but this does not appear to be the case. The Bavarian longitudinal study also showed that people born VPT/VLBW tend to be more introverted, meaning they are more withdrawn, seek less social interaction, and spend more time alone. This finding has been confirmed by four additional studies. This may indicate that the brains of VPT/VLBW individuals are more sensitive to high levels of social stimulation. It was also found that they ruminate and worry about everyday matters more often.

Taken together, we can consider how to create new ways to make meeting potential partners and new friends easier in adulthood, such as groups tailored for more introverted people, specialized dating apps.

Gonen, E., Twilhaar, E. S., Baumann, N., Busch, B., Bartmann, P., & Wolke, D. Veränderungen in sozialen Beziehungen im Alter von 26 bis 34 Jahren bei sehr früh geborenen Erwachsenen. Pädiatrische und perinatale Epidemiologie, n/a(n/a). https://doi.org/https://doi.org/10.1111/ppe.13133

Liu, Y., Realo, A., Mendonça, M., Baumann, N., Bartmann, P., Räikkönen, K., Heinonen, K., Robinson, R., Marlow, N., Johnson, S., Ni, Y., Kajantie, E., Hovi, P., Tikanmäki, M., & Wolke, D. Der Einfluss einer sehr frühen Geburt auf das Fünf-Faktoren-Modell der Persönlichkeitsmerkmale: Eine Metaanalyse der Daten einzelner Teilnehmer. European Journal of Personality, 0(0), 08902070241280101. https://doi.org/10.1177/08902070241280101

2. How we study the Claustrum using measurements of directed water movement in the brain — and how its cell density is altered in adults born preterm

Location and role of the claustrum in the brain

The claustrum (derived from Latin for “closed” or “hidden”) is a very small brain structure, deeply embedded in both hemispheres behind a portion of the cerebral cortex called the insula (see Figure 1A). Although tiny, the claustrum appears to play an important role in controlling brain activity. This becomes clear when looking at its connectivity: The claustrum is the most highly connected region in the human brain. This means it is involved in functions that require the coordination of many widespread brain areas, such as perceptual processing, attention or deep sleep, when all parts of the brain are organized in delta waves.

Challenges in studying the claustrum

Because it is so small and so extensively connected, studying the human claustrum is extremely challenging. In close collaboration with experts in medical image analysis at the Technical University of Munich and using your MRI scans at age 26 we developed techniques that allow us to precisely characterize the anatomical connections between the claustrum and other brain regions. We used diffusionweighted MRI, which measures the movement of water molecules in all directions in all areas of the brain. By tracking these water movements, we were able to reconstruct neural pathways of the brain and especially of the claustrum. Thanks to this method, we were able to demonstrate that the human claustrum connects with many brain regions — mostly within the same hemisphere, but also across hemispheres. We are now investigating whether claustrum connectivity differs in individuals born preterm.

Results: Connections and structure of the claustrum

In addition to connectivity, we also studied the volume and microstructure of the claustrum in adults born preterm versus those born at term. While claustrum volume did not differ between preterm and full-term adults, we detected altered water diffusion (i.e. movement) in the claustrum of adults born preterm (Figure 1B). On average, adults born preterm exhibited higher water movement. This suggests lower cell density, as fewer cells mean that water molecules experience less obstruction and can move more freely. We further found that that this was associated with birthweight: the lower the birthweight, the greater the water diffusion in the claustrum. Exactly how being born prematurely influences cell density in the claustrum remains unclear.

Future Directions and applications

In summary, your participation in the Bavarian Longitudinal Study has made it possible for us to map the connections and structure of the claustrum and depict how this structure may be altered in those born preterm. We are now exploring whether this knowledge could be used to better assess brain health after birth.

References:

Wendt, Jil & Neubauer, Antonia & Hedderich, Dennis & Schmitz-Koep, Benita & Ayyildiz, Sevilay & Schinz, David & Hippen, Rebecca & Daamen, Marcel & Boecker, Henning & Zimmer, Claus & Wolke, Dieter & Bartmann, Peter & Sorg, Christian & Menegaux, Aurore. (2024). Human Claustrum Connections: Robust In Vivo Detection by DWI‐Based Tractography in Two Large Samples. Human Brain Mapping. 45. 10.1002/hbm.70042

Hedderich, Dennis & Menegaux, Aurore & Li, Hongwei & Schmitz-Koep, Benita & Stämpfli, Philipp & Bäuml, Josef & Berndt, Maria & Bäuerlein, Felix & Grothe, Michel & Dyrba, Martin & Avram, Mihai & Boecker, Henning & Daamen, Marcel & Zimmer, Claus & Bartmann, Peter & Wolke, Dieter & Sorg, Christian. (2021). Aberrant Claustrum Microstructure in Humans after Premature Birth. Cerebral Cortex. 31. 10.1093/cercor/bhab178

Figure 1. The claustrum is altered in adults born preterm.

A: Three-dimensional anatomical depiction of the claustrum’s location

B: Measurement of the claustrum using T1-weighted and diffusionweighted MRI

C: Top: Claustrum volume is unchanged between full-term (FT), very preterm (VP), and verylowbirthweight (VLBW) adults. Bottom: Average mean diffusivity (MD) is increased in VP and VLBW adults.

Your opinion matters: Feedback about study participation

As in previous years, we welcome any questions you may have about the study results or about any aspect of the assessments. You can reach us at BEST@ukbonn.de or via telephone at 0228 – 287 33533 (with call forwarding or answering machine).

We look forward to seeing you again next year not only by telephone, but also in person during the assessments in Munich, and of course especially at the summer festival.

Christmas and the turn of the year are now approaching rapidly. We wish you time and calmness to enjoy these still very special days. For the year 2025, we send our best wishes to you and your loved ones, stay healthy and optimistic and remember that even when the future seems difficult, there is always a way forward. We look forward to continuing our contact with you.

With kind regards

P.S. Please inform us of any changes to your contact details (address, email, telephone) via  BEST@ukbonn.de or  +49 (0)228 – 287 33533. Thank you very much!