Biology subjects

Kühnel, A.

Publications and source records attributed to Kühnel, A..

6 recordsLinked to original sources

bioRxiv2026

Stronger brain responses to acute stress reflect greater everyday stress variability

Laboratory stress tasks are widely used to assess individual differences in acute stress reactivity, yet it remains unclear how these responses correspond to stress experienced in everyday life. Here, we combined the Montreal imaging stress task (MIST) with ecological momentary assessment (EMA) over three months to assess acute and everyday stress in 67 healthy women. Greater within-person variability in everyday stress, but not average stress levels, were associated with stronger overall stress-related brain responses (b = 0.73, p = .039), with a whole-brain association particularly evident in the bilateral caudate (rROI = .32, pcluster.FWE < .001). Greater everyday stress variability was also associated with stronger stress-related functional connectivity between the ventromedial prefrontal cortex (vmPFC) and parietal and posterior medial regions (pcluster.FWE < .001). We conclude that acute neural stress responses relate more closely to fluctuations in perceived stress than to how stressed an individual feels on average. This suggests that laboratory stress tasks capture acute stress responsivity that is distinct from average stress exposure, highlighting the importance of considering what these tasks measure when interpreting individual differences in acute stress responses.

neuroscience↗

bioRxiv2025

Non-invasive vagus nerve stimulation modulates Pavlovian bias in a state-dependent manner

The vagus nerve transmits vital signals between organ systems of the body and the brain. Despite growing interest in non-invasive transcutaneous vagus nerve stimulation (tVNS) for treatments of various disorders, it is not known whether its modulatory effects on behavior are dependent on bodily states. Here, we used a single-blind randomized crossover design with two within-participant factors, stimulation (right tVNS vs. sham) and metabolic state (water vs. caloric load), to investigate 54 healthy participants (210 sessions). To evaluate state-dependent changes in reinforcement learning, we used a valenced go/no-go task. Performance on this task can be used to estimate a Pavlovian choice bias, which captures improved performance for valence-congruent actions (e.g., go to win rewards) versus valence-incongruent actions (e.g., no-go to win rewards) and has been associated with dopaminergic neurotransmission. In line with theorized state-dependency of tVNS-induced changes, we observed that tVNS decreased Pavlovian response biases (Go x Win) after the caloric load (Stimulation x Load: p =.038). Taking into account individual changes in hunger but not satiety ratings best captured behavioral modulation, indicating that this modulatory effect could be driven by motivational effects related to metabolic interoception (sensed "need"). We conclude that right tVNS decreases Pavlovian response biases if the body is in a postprandial, but not a fasting state. Since fasting and Pavlovian biases have been previously associated with elevated dopamine neurotransmission, our results call for additional research on state-dependent motivational effects of tVNS to optimize interventions.

neuroscience↗

bioRxiv2025

Higher glucose levels buffer against everyday stress load

Adaptive stress responses are dependent on the availability of energy and the bodys effectiveness in metabolizing glucose as fuel. However, it is not well understood if glucose levels contribute to the functional regulation of daily stress in healthy individuals. Here, we used 4,307 ratings of stress during a four-week period of ecological momentary assessment (EMA) with concurrent recordings from continuous glucose monitoring (CGM) in 91 participants (47 women). In accordance with the hypothesized metabolic link, we found that higher glucose levels were associated with lower self-reported stress (b = -.038, p = .035, controlling for mood). Crucially, dynamic changes in glucose levels also precipitated subsequent increases in stress levels (0-2h before EMA: p = .013; incremental effect 10-12h before: p < .001), with lower glucose levels associated with subsequent stress increases and elevated glucose with stress relief, highlighting the potential of monitoring physiological biosensor data to improve adaptive stress regulation. We conclude that metabolic signals, such as glucose, play an important role in channeling stress responsiveness in healthy adults, pointing to a pivotal avenue for improved interventions to avoid excessive stress experiences.

neuroscience↗

bioRxiv2025

Metabolic state shapes cortisol reactivity to acute stress: A systematic review and meta-analysis of metabolic and hormonal modulators

Individual variability in cortisol stress responses is shaped by multiple physiological factors. Yet the interaction with metabolic and hormonal states remains poorly understood. Therefore, we conducted a systematic review and meta-analysis to examine how metabolic factors (particularly glucose) and sex hormone levels (progesterone and estradiol) influence cortisol reactivity to acute stress. We identified 21 studies (N = 1216 participants) and conducted random-effects meta-analyses for metabolic and hormonal states. Across studies, glucose administration was associated with a significant increase in cortisol responses to acute stress compared to fasting or non-glucose control conditions (d = 0.30, 95% CI = [0.05, 0.60], BF10 = 2.42, NNT = 10.63). In contrast, the effects of sex hormones on cortisol responses were smaller and more variable, with both progesterone and estradiol showing weak and inconsistent associations. Our results highlight a robust modulatory role of metabolic state, specifically glucose availability, on HPA axis reactivity, while evidence for sex hormone effects remains inconclusive. Future research should focus on better harmonization of designs concerning sex hormones and systematically examine interactions between metabolic and hormonal states to better explain sex differences in the prevalences of metabolic and stress-related disorders.

physiology↗

bioRxiv2021

Acute vagus nerve stimulation does not affect liking or wanting ratings of food in healthy participants

The vagus nerve plays a vital role in the regulation of food intake and vagal afferent signals may help regulate food cue reactivity by providing negative homeostatic feedback. Despite strong evidence from preclinical studies on vagal afferent "satiety" signals in guiding food intake, evidence from human studies is largely inconclusive to date. Here, we investigated the acute effects of left or right transcutaneous auricular vagus nerve stimulation (taVNS) on subjective ratings of wanting and liking of various food and non-food items in 82 healthy participants (46 women, MBMI = 23.1 kg/m2). In contrast to previous reports in patients with depression, we found moderate to anecdotal evidence supporting the absence of taVNS-induced changes in food ratings. To test whether the absence of taVNS effects on food ratings is due to heterogeneity in the sample, we conducted post hoc subgroup analyses by splitting the data according to stimulation side and sex (between-subject factors) as well as caloric density, perceived healthiness, and flavor (sweet vs. savory) of the food (within-subject factors). This multiverse analysis largely supported the absence of taVNS-induced changes since the strongest subgroup effects provided only anecdotal evidence in favor of taVNS-induced changes. We conclude that acute taVNS only has a marginal effect on subjective ratings of food, suggesting that it is an unlikely mechanism for the reported long-term effects of VNS on body weight. In light of an absence of acute taVNS effects on food craving, our results call for future research on the correspondence between acute and chronic effects of vagal afferent stimulation.

neuroscience↗

bioRxiv2020

Non-invasive vagus nerve stimulation boosts mood recovery after effort exertion

Mood plays an important role in our life which is illustrated by the disruptive impact of aberrant mood states in depression. Although vagus nerve stimulation (VNS) has been shown to improve symptoms of depression, the exact mechanism is still elusive, and it is an open question whether non-invasive VNS could be used to swiftly and robustly improve mood. Here, we investigated the effect of left- and right-sided transcutaneous auricular VNS (taVNS) versus a sham control condition on mood after exertion of physical and cognitive effort in 82 healthy participants (randomized cross-over design). Using linear mixed-effects and hierarchical Bayesian analyses of mood ratings, we found that 90 min of either left-sided or right-sided taVNS improved positive mood (b = 5.11, 95% credible interval, CI [1.39, 9.01], 9.6% improvement relative to the mood intercept, BF10= 7.69, pLME = .017), yet only during the post stimulation phase. Moreover, lower baseline scores of positive mood were associated with greater taVNS-induced improvements in motivation (r = -.42, 95% CI [-.58, -.21], BF10 = 249). We conclude that taVNS boosts mood after a prolonged period of effort exertion with concurrent stimulation and that acute motivational effects of taVNS are partly dependent on initial mood states. Collectively, our results show that taVNS may help quickly improve affect after a mood challenge, potentially by modulating interoceptive signals contributing to reappraisal of effortful behavior. This suggests that taVNS could be a useful add-on to current behavioral therapies.

neuroscience↗