Rumination Out Loud? Linguistic, Neural, and Psychophysiological Correlates of the Think-Aloud Paradigm

Stress and rumination are closely linked and contribute to the development and maintenance of mental disorders, yet assessing rumination in an ecologically valid way remains challenging. Conducting the think aloud paradigm (TAP) following the Trier Social Stress Test (TSST) allows for the real-time evaluation of ruminative responses, providing insights beyond traditional self-report measures. This study aimed to investigate ruminative responses to the TSST using the TAP, while simultaneously assessing psychological (stress, affect, state rumination), physiological (heart rate), and neural data with functional near-infrared spectroscopy (fNIRS). For this, a total of 58 healthy participants (mean age 23.47 years (SD = 3.87), 63.8% females) completed a 10-min resting-state period both before and after the TSST, verbalizing their thoughts. In response to the TSST, we observed significant increases in stress, state rumination, negative affect, heart rate, and cortical oxygenation in all regions of interest except the inferior frontal gyrus (IFG), reflecting a successful stress induction. Although we observed higher stress, state rumination, and negative affect, alongside lower positive affect in high ruminators using questionnaires, linguistic evaluation of the verbalized thought content showed no significant time effects but revealed generally lower sentiment scores for high ruminators and only partly showed differences dependent on trait rumination levels. With respect to neural correlates, we observed prefrontal hypoactivation under stress in medium and high compared to low ruminators. Comparing the results with previous studies, the administration of the TAP following the TSST seems to function as a form of emotion regulation, thereby reducing state rumination. Further studies are required to explore the underlying mechanisms.