Biology subjects

Menger, N. S.

Publications and source records attributed to Menger, N. S..

3 recordsLinked to original sources

bioRxiv2025

Elusive scent of fear: no evidence of olfactory reversal conditioning in humans

Reversal learning offers a window into how associations are acquired, updated, and overwritten. Because olfactory inputs bypass much of the thalamus and are tightly linked to emotion, we examined whether humans can flexibly form and subsequently reverse aversive associations to smells. Thirty healthy adults underwent an olfactory reversal conditioning protocol in which one neutral odor (CS+) was followed by a 90 dB aversive sound (US) and a second odor (CS-) was not. After five blocks the contingencies were reversed. Throughout 300 trials we collected ratings of pleasantness and intensity together with autonomic physiological indices (skin conductance, ECG, photoplethysmography, respiration), facial EMG, and 64-channel EEG. Contrary to expectations, pleasantness, intensity, and all autonomic or facial muscle measures failed to differentiate CS+ and CS-either before or after reversal (all p > .01). Event-related potentials, alpha suppression, heart rate and pulse wave responses likewise showed no CS specificity. Only multivariate classifiers: trained (i) on the time-domain EEG signal and (ii) on alpha-band activity, separately, distinguished CS+ from CS-at above-chance levels in late post-stimulus intervals. These neural signatures did not translate into overt physiological or behavioural differences. The pattern suggests that, at least with neutral odors and an auditory US, olfactory fear learning is subtle, spatially variable across the cortex, and easily masked in group-level averages. Our findings highlight both the promise of multivariate EEG for detecting fragile olfactory associations and the challenge of eliciting robust conditioned responses with cross-modal (odor-sound) pairings.

neuroscience↗

bioRxiv2024

Missing what is right under your nose: failed appetitive and aversive audio-olfactory conditioning in humans

The comparison of physiological mechanisms underlying appetitive and aversive conditioning is often challenging due to the involvement of stimuli from different modalities with potentially disparate effective mechanisms (e.g., pain stimuli versus monetary rewards). The olfactory system offers a unique opportunity to examine both types of conditioning in humans, as isointense odors can serve as comparably pleasant and unpleasant stimuli. To study physiological and behavioral responses during appetitive and aversive learning, we employed odors as unconditioned stimuli (US) in a within-subjects design, measuring various conditioned physiological responses including skin conductance, heart rate, pulse wave amplitude, respiration, fear-potentiated startle, postauricular reflex, facial electromyography as well as event-related potentials, and auditory steady-state responses (ASSR) derived from electroencephalography. We conducted four experiments with a total of 95 participants, presenting three neutral sounds paired with either a pleasant odor, unpleasant odor, or odorless air. The first experiment involved uninstructed participants and frequency-modulated conditioned stimuli (CS) for ASSR analysis. In the second experiment, we omitted the frequency modulation and startle probe. The third experiment included pre-experiment instruction on CS-US contingencies, while the fourth employed a delayed conditioning paradigm in contrast to the other three experiments. Our results revealed differences between CS+ and CS-only in the fear-potentiated startle response in Experiment 3. No other effects were found. The minimal or absent learning effects observed across multiple peripheral and neural physiological measures may be attributed to the extra-thalamic nature of olfactory pathways and the subsequent difficulty in forming associations with auditory stimuli. Impact statementIn a series of 4 experiments, we explored the neurophysiological differences between appetitive and aversive conditioning. Yet, none of the experiments showed effective conditioning. We hypothesize that the lack of learning effects is attributed to the inherent difficulty in forming associations between auditory and olfactory inputs.

neuroscience↗

bioRxiv2024

Contingency awareness shapes neural responses in fear conditioning

Contingency awareness refers to an observers ability to identify the association between a conditioned (CS) and an unconditioned stimulus (US). A widely held belief in human fear conditioning is that this form of associative learning may occur independently of contingency awareness. To test this hypothesis, in this preregistered study (https://osf.io/vywq7), we recorded electroencephalography (EEG) during a task, where participants were presented with compounds of a word (drawn from two semantic categories) and tactile stimulation (vibration), followed by either a neutral sound (US-) or a loud noise (US+). Based on interviews, participants were divided into an aware (N=50) and an unaware (N=31) group. Only the aware group showed evidence of learning at the neural level, notably a larger stimulus-preceding negativity developing before US+ and a stronger theta response to vibrations predicting US+. The aware group also showed stronger alpha and beta suppression around the vibrations and a weaker theta response to US+, possibly indicating heightened attention to the cue and the violation/confirmation of expectation. Group differences in alpha and beta suppression were already present before the aversive learning began, suggesting that elevated attention may precede and facilitate awareness. Personality tests showed that elevated anxiety, neuroticism, higher intolerance of uncertainty, or harm avoidance are not predictive to the acquisition of contingency awareness. Our findings support the notion that fear conditioning, as reflected in cortical measures, cannot occur without contingency awareness.

neuroscience↗