Electrical neuroimaging of memory discrimination based on single-trial multisensory learning

Micah Murray, Antonia Thelen
Elsevier, 2012
Article

Résumé

Multisensory experiences influence subsequent memory performance and brain responses. Studies have thus far concentrated on semantically congruent pairings, leaving unresolved the influence of stimulus pairing and memory sub-types. Here, we paired images with unique, meaningless sounds during a continuous recognition task to determine if purely episodic, single-trial multisensory experiences can incidentally impact subsequent visual object discrimination. Psychophysics and electrical neuroimaging analyses of visual evoked potentials (VEPs) compared responses to repeated images either paired or not with a meaningless sound during initial encounters. Recognition accuracy was significantly impaired for images initially presented as multisensory pairs and could not be explained in terms of differential attention or transfer of effects from encoding to retrieval. VEP modulations occurred at 100-130ms and 270-310ms and stemmed from topographic differences indicative of network configuration changes within the brain. Distributed source estimations localized the earlier effect to regions of the right posterior temporal gyrus (STG) and the later effect to regions of the middle temporal gyrus (MTG). Responses in these regions were stronger for images previously encountered as multisensory pairs. Only the later effect correlated with performance such that greater MTG activity in response to repeated visual stimuli was linked with greater performance decrements. The present findings suggest that brain networks involved in this discrimination may critically depend on whether multisensory events facilitate or impair later visual memory performance. More generally, the data support models whereby effects of multisensory interactions persist to incidentally affect subsequent behavior as well as visual processing during its initial stages.

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https://infoscience.epfl.ch/record/177612?ln=fr

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Micah Murray, Antonia Thelen
Elsevier, 2012
Article

Résumé

Official source

https://infoscience.epfl.ch/record/177612?ln=fr

À propos de ce résultat

Concepts associés (16)

Concepts associés

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Publications associées (8)

Publications associées

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Bodily self-consciousness is linked to multisensory integration and is particularly dependent on vestibular perception providing the brain with the main sensory cues about body motion and location in space. Vestibular and visual inputs are permanently balanced and integrated to encode the most optimal representation of the external world and of the observer in the central nervous system. Vection, an illusory self-motion experience induced only by visual stimuli, illustrates the fact that the visual and the vestibular systems share common neural underpinnings and a similar phenomenology. Optokinetic stimulation inducing vection and direct vestibular stimulation induce whole-body motion sensations that can be used to explore multisensory interactions. A failure in visuo-vestibular integration, artificially induced by the methods of cognitive psychology or in pathological conditions, has also been reported to altered own body perception and bodily self-consciousness. The respective contributions of the vestibular and visual systems to bodily self-consciousness amongst other polymodal sensory mechanisms, and the neural correlates of visuo-vestibular convergence, should be better understood. We first performed a neuroimaging study of brain regions where optokinetic and vestibular stimuli converge, using 7T functional magnetic resonance imaging in individual subjects. We identified three main regions of convergence: (1) the depth of supramarginal gyrus or retroinsular cortex, (2) the surface of supramarginal gyrus at the temporo-parietal junction, (3) and the posterior part of middle temporal gyrus and superior temporal sulcus. Then, we aimed to induce the embodiment of an external fake rubber hand through visuo-tactile conflict - the so-called rubber hand illusion paradigm, and studied how this integration is modulated by vection. Subjects experiencing vection in the direction of the rubber hand mislocalised the position of their real hand towards the rubber hand indicating that visuo-vestibular stimuli can enhance visuo-tactile integration. We also investigated if visuo-proprioceptive and tactile integration in peripersonal space could be dynamically updated based on the congruency of visual and proprioceptive feedback. A pair of rubber hands or feet provided visual feedback. Fake and real limbs were crossed or uncrossed. We showed that sensory cues were integrated in peripersonal space, dynamically reshaped but only for hands. Finally, we investigated a rare case of an illusory own body perception in an epileptic patient suffering from multiple daily disembodiments during seizures. Seizures were associated to a focal cortical microdysplasia juxtaposed to a developmental venous anomaly in the left angular gyrus, a brain region known to be important for visuo-vestibular integration and bodily self-consciousness. Our results characterize the inferior parietal lobule as a crucial structure in merging visual, vestibular, tactile and proprioceptive inputs, allowing the emergence of the global and unified experience of being âI.â Multisensory body representation can be reshaped transiently using visual and vestibular signals or in relation to a medical condition affecting the temporo-parietal junction. The integration of visual and vestibular signals, aims to adapt dynamically our internal representations to constant changes occurring in our environment.

EPFL2015

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Vestibular contribution to bodily self-consciousness and multisensory cortical processing

Christian Pfeiffer

How does the self relate to the body? Bodily self-consciousness, i.e. the sense of being a subject bound to a body, involves a first-person perspective (1PP), i.e. the sense of being directed at the world. Prior research suggests that bodily self-consciousness depends on brain mechanisms integrating multisensory bodily signals. However, the specific multisensory mechanisms of 1PP are poorly understood. Here, I defend the thesis that the vestibular system, i.e. the sensory system encoding rotational and linear accelerations of the head, contributes to 1PP and related multisensory processing in the brain. The first part of my thesis presents experimental evidence showing that 1PP was influenced by multisensory conflict about the direction of gravity and the location of the body. 1PP depended on integrated visual-vestibular signals and was functionally distinct from another aspect of bodily self-consciousness: self-identification, i.e. the feeling that a particular body is âmineâ. The second part of my thesis presents the electrical neural correlates by which vestibular stimulation affected somatosensory and visual cortical processing. Passive whole-body yaw rotation naturally and selectively stimulated the vestibular system while the evoked responses to somatosensory or visual stimuli were recorded by electroencephalography. Electrical neuroimaging analysis showed temporal-specific vestibular effects on somatosensory and visual evoked potentials, localized by source estimations to distinct regions of the somatosensory, visual, and vestibular cortical networks. Collectively, the results from my thesis suggest that the vestibular system contributes to 1PP and multisensory cortical processing and imply that the vestibular system should not be neglected when studying higher brain function and neurobiological mechanisms of consciousness.

EPFL2015

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Act Quickly, Decide Later: Long-latency Visual Processing Underlies Perceptual Decisions but Not Reflexive Behavior

Humans largely guide their behavior by their visual representation of the world. Recent studies have shown that visual information can trigger behavior within 150 msec, suggesting that visually guided responses to external events, in fact, precede conscious awareness of those events. However, is such a view correct? By using a texture discrimination task, we show that the brain relies on long-latency visual processing in order to guide perceptual decisions. Decreasing stimulus saliency leads to selective changes in long-latency visually evoked potential components reflecting scene segmentation. These latency changes are accompanied by almost equal changes in simple RTs and points of subjective simultaneity. Furthermore, we find a strong correlation between individual RTs and the latencies of scene segmentation related components in the visually evoked potentials, showing that the processes underlying these late brain potentials are critical in triggering a response. However, using the same texture stimuli in an antisaccade task, we found that reflexive, but erroneous, prosaccades, but not antisaccades, can be triggered by earlier visual processes. In other words: The brain can act quickly, but decides late. Differences between our study and earlier findings suggesting that action precedes conscious awareness can be explained by assuming that task demands determine whether a fast and unconscious, or a slower and conscious, representation is used to initiate a visually guided response.

2011

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EPFL2015