Weijs, M. L. | bioRxiv Science

bioRxiv2024

Pupil self-regulation modulates markers of cortical excitability and cortical arousal

The brains arousal state (i.e., central arousal) is regulated by multiple neuromodulatory nuclei in the brainstem and significantly influences high-level cognitive processes. By exploiting the mechanistic connection between the locus coeruleus (LC), a key regulator of central arousal, and pupil dynamics, we recently demonstrated that participants can gain volitional control over arousal-regulating centers including the LC using a pupil-based biofeedback approach. Here, we test whether pupil-based biofeedback modulates electrophysiological markers of cortical excitability, cortical arousal, and phasic LC activity. Combining pupil-based biofeedback with single-pulse TMS, EEG recordings, and an auditory oddball task revealed three main results: pupil self-regulation significantly modulates (i) cortical excitability, (ii) the EEG spectral slope, a marker of cortical arousal, and (iii) the P300 response to target tones, an event-related potential suggested to be tightly linked to phasic LC activity. Interestingly, pupil self-regulation strength was linearly linked to the modulation of the spectral slope, suggesting a common physiological mechanism. Here, we have shown that pupil-based biofeedback modulates fundamental aspects of brain function. Whether this method could further be used to modulate these aspects in case of disturbances associated with neurological and psychiatric disorders needs to be investigated in future studies.

neuroscience↗

bioRxiv2019

Achronopresence: how temporal visuotactile and visuomotor mismatches modulate embodiment

The loss of body ownership, the feeling that your body and its limbs no longer belong to you, presents a severe clinical condition that has proven difficult to study directly. We here propose a novel paradigm using mixed reality to interfere with natural embodiment using temporally conflicting sensory signals from the own hand. In Experiment 1 we investigated how such a mismatch affects phenomenological and physiological aspects of embodiment, and identified its most important dimensions using a principle component analysis. The results suggest that such a mismatch induces a strong reduction in embodiment accompanied by an increase in feelings of disownership and deafference, which was, however, not reflected in physiological changes. In Experiment 2 we refined the paradigm to measure perceptual thresholds for temporal mismatches and compared how different multimodal, mismatching information alters the sense of embodiment. The results showed that while visual delay decreased embodiment both while actively moving and during passive touch, the effect was stronger for the former. Our results extend previous findings as they demonstrate that a sense of disembodiment can be induced through controlled multimodal mismatches about ones own body and more so during active movement as compared to passive touch. Based on the ecologically more valid protocol we propose here, we argue that such a sense of disembodiment may fundamentally differ from disownership sensations as discussed in the rubber hand illusion literature, and emphasize its clinical relevance. This might importantly advance the current debate on the relative contribution of different modalities to our sense of body and its plasticity.

neuroscience↗