Biology subjects

Amedi, A.

Publications and source records attributed to Amedi, A..

7 recordsLinked to original sources

bioRxiv2025

The brain dynamics of congenitally blind people seeing faces with sound

Sensory substitution devices (SSDs) convert images to sounds to equip blind individuals with nominally visual functions, like face or letter sensitivity. Prior studies showed that image-to-sound SSDs engage cortices ordinarily specialised for visual functions. However, the brain dynamics of SSD-supported perception remains unknown. Either visual cortices are the first locus of discrimination of SSD percepts, or their activation is a byproduct of perceptual processes unfurling elsewhere, such as in auditory cortices. Resolving this uncertainty is critical for understanding the contribution of visual cortices to mechanisms subserving SSD-induced perceptions in the blind. Using electrical neuroimaging of EEG data from congenitally blind adults, we show for the first time that visual cortices are the earliest site of face and letter sensitivity when conveyed via SSDs, though with distinct temporal dynamics and spatial localizations. In the case of faces versus scrambled faces, differences first manifested at 460ms post-stimulus onset as topographic EEG modulations that were in turn localized to a network of right-hemisphere regions, including the fusiform face area (FFA) as well as lateral occipital cortices. In the case of discerning vertically versus horizontally oriented letter shapes, differences first manifested at 370ms post-stimulus onset as topographic EEG modulations that were localized to a network of left-hemisphere regions, including the occipital pole and the occipito-temporal junction extending into the angular gyrus. Notably, early-latency auditory evoked potentials did not differ based on visual properties of the soundscapes. These collective data support the proposition that responses to soundscapes are routed to brain circuits ordinarily specialized for processing visual information and that these circuits are the loci of the initial discriminant processes. By providing the temporal dynamics of SSD perception, our findings provide unique evidence for the theory that cortices are characterised by task-contingent functional organisation. HighlightsO_LISensory substitution devices (SSDs) provide the blind access to visual information C_LIO_LIBrain dynamics in visual cortices to SSD-conveyed object images are unknown C_LIO_LIEarly EEG sensitivity for faces and letters was localized to the visual cortex C_LIO_LIThe blind visual cortex takes part in early SSD processing for visual categories C_LI eTOC blurbWe characterise for the first time the brain dynamics of the blind using soundscapes for face and letter discrimination. Faces recruited the FFA at 460ms post-stimulus onset, whereas letters recruited the occipital pole, occipito-temporal junction, and angular gyrus at 370ms post-stimulus onset. Our findings of the temporal dynamics of SSD perception uniquely support the theory that cortices are characterised by task-selective sensory-independent functional organisation.

neuroscience↗

bioRxiv2024

Resting-state functional connectivity changes following audio-tactile speech training

Understanding speech in background noise is a challenging task, especially if the signal is also distorted. In a series of previous studies we have shown that comprehension can improve if simultaneously to the auditory speech, the person receives speech-extracted low-frequency signals on fingertips. The effect increases after short audio-tactile speech training. Here we use resting-state functional magnetic resonance, measuring spontaneous low-frequency oscillations in the brain while at rest, to assess training-induced changes in functional connectivity. We show enhanced connectivity within a right-hemisphere cluster encompassing the middle temporal motion area (MT), and the extrastriate body area (EBA), and lateral occipital cortex (LOC), which before training is found to be more connected to bilateral dorsal anterior insula. Furthermore, early visual areas are found to switch from increased connectivity with the auditory cortex before, to increased connectivity with an association sensory/multisensory parietal hub, contralateral to the palm receiving vibrotactile inputs, after. Also the right sensorimotor cortex, including finger representations, is more connected internally after training. The results alltogether can be interpreted within two main complementary frameworks. One, speech-specific, relates to the pre-existing brain connectivity for audio-visual speech processing, including early visual, motion and body regions for lip-reading and gesture analysis in difficult acoustic conditions, which the new audio-tactile speech network might be built upon. The other refers to spatial/body awareness and audio-tactile integration, including in the revealed parietal and insular regions. It is possible that an extended training period may be necessary to more effectively strengthen direct connections between the auditory and sensorimotor brain regions, for the utterly novel speech comprehension task. The outcomes of the study can be relevant for both basic neuroscience, as well as development of rehabilitation tools for the hearing impaired population.

neuroscience↗

bioRxiv2024

Neuronal basis of audio-tactile speech perception

Since childhood, we experience speech as a combination of audio and visual signals, with visual cues particularly beneficial in difficult auditory conditions. This study investigates an alternative multisensory context of speech, and namely audio-tactile, which could prove beneficial for rehabilitation in the hearing impaired population. We show improved understanding of distorted speech in background noise, when combined with low-frequency speech-extracted vibrotactile stimulation delivered on fingertips. The quick effect might be related to the fact that both auditory and tactile signals contain the same type of information. Changes in functional connectivity due to audio-tactile speech training are primarily observed in the visual system, including early visual regions, lateral occipital cortex, middle temporal motion area, and the extrastriate body area. These effects, despite lack of visual input during the task, possibly reflect automatic involvement of areas supporting lip-reading and spatial aspects of language, such as gesture observation, in difficult acoustic conditions. For audio-tactile integration we show increased connectivity of a sensorimotor hub representing the entire body, with the parietal system of motor planning based on multisensory inputs, along with several visual areas. After training, the sensorimotor connectivity increases with high-order and language-related frontal and temporal regions. Overall, the results suggest that the new audio-tactile speech task activates regions that partially overlap with the established brain network for audio-visual speech processing. This further indicates that neuronal plasticity related to perceptual learning is first built upon an existing structural and functional blueprint for connectivity. Further effects reflect task-specific behaviour related to body and spatial perception, as well as tactile signal processing. Possibly, a longer training regime is required to strengthen direct pathways between the auditory and sensorimotor brain regions during audio-tactile speech processing.

neuroscience↗

bioRxiv2024

Training interoceptive awareness with real-time haptic vs. visual heartbeat feedback

The perception of signals from within the body, known as interoception, is increasingly recognized as a prerequisite for physical and mental health. The study is dedicated to the development of effective technological approaches for enhancing interoceptive awareness. We provide evidence of the effectiveness and practical feasibility of a novel real-time haptic heartbeat supplementation technology combining principles of biofeedback and sensory enhancement. In a randomized controlled study, we applied the developed naturalistic haptic feedback on a group of 30 adults, while another group of 30 adults received more traditional real-time visual heartbeat feedback. A single session of haptic, but not visual heartbeat feedback resulted in increased interoceptive accuracy and confidence, as measured by the heart rate discrimination task, and in a shift of attention towards the body. Participants rated the developed technology as more helpful and pleasant than the visual feedback, thus indicating high user satisfaction. The study highlights the importance of matching sensory characteristics of the feedback to the natural bodily prototype. Our work suggests that real-time haptic feedback might be a superior approach to strengthen mind-body interaction in interventions for physical and mental health. HighlightsO_LIWe developed a naturalistic real-time haptic feedback system for enhancing cardiac interoception. C_LIO_LIThe intervention resulted in higher interoceptive accuracy and confidence, and in a shift of attention towards the body. C_LIO_LIHaptic feedback outperformed traditional visual feedback in efficacy and user satisfaction. C_LIO_LIResults of the study indicate the importance of feedback sensory characteristics in mind-body technologies. C_LI

neuroscience↗

bioRxiv2023

Longitudinal stability of individual brain plasticity patterns in blindness

The primary visual cortex (V1) in individuals born blind is engaged in a wide spectrum of tasks and sensory modalities, including audition, touch, language, and memory. This widespread involvement raises questions regarding the constancy of its role and whether it might exhibit flexibility in its function over time, connecting to diverse network functions in response to task-specific demands. This would suggest that reorganized V1 takes on a role similar to cognitive multiple-demand system regions. Alternatively, it is possible that the varying patterns of plasticity observed in the blind V1 can be attributed to individual factors, whereby different blind individuals recruit V1 for different functions, highlighting the immense idiosyncrasy of plasticity. In support of this second account, we have recently shown that V1 functional connectivity varies greatly across blind individuals. But do these represent stable individual patterns of plasticity or merely instantaneous changes, for a multiple-demand system now inhabiting V1? Here we tested if individual connectivity patterns from the visual cortex of blind individuals are stable over time. We show that over two years, fMRI functional connectivity from the primary visual cortex is unique and highly stable in a small sample of repeatedly sampled congenitally blind individuals. Further, using multivoxel pattern analysis, we demonstrate that the unique reorganization patterns of these individuals allow decoding of participant identity. Together with recent evidence for substantial individual differences in visual cortex connectivity, this indicates there may be a consistent role for the visual cortex in blindness, which may differ for each individual. Further, it suggests that the variability in visual reorganization in blindness across individuals could be used to seek stable neuromarkers for sight rehabilitation and assistive approaches.

neuroscience↗

bioRxiv2020

Proprioception Has Limited Influence on Tactile Reference Frame Selection

Perceiving the spatial location and physical dimensions of objects that we touch is crucial for goal-directed actions. To achieve this, our brain transforms skin-based coordinates into a reference frame by integrating visual and proprioceptive cues, a process known as tactile remapping. In the current study, we examine the role of proprioception in the remapping process when information from the more dominant visual modality is withheld. We developed a new visual-to-touch sensory substitution device and asked participants to perform a spatial localization task in three different arm postures that included posture switches between blocks of trials. We observed that in the absence of visual information novel proprioceptive inputs can be overridden after switching postures. This behavior demonstrates effective top-down modulations of proprioception and points to the unequal contribution of different sensory modalities to tactile remapping.

neuroscience↗

bioRxiv2018

Human Navigation Without and With Vision - the Role of Visual Experience and Visual Regions

Human navigation relies on a wide range of visual retinotopic cortical regions yet the precise role that these regions play in navigation remains unclear. Are these regions mainly sensory input channels or also modality-independent spatial processing centers? Accordingly, will they be recruited for navigation also without vision, such as via audition? Will visual experience, or the lack thereof, affect this recruitment? Sighted, congenitally blind and sighted-blindfolded participants actively navigated virtual mazes during fMRI scanning before and after navigating them in the real world. Participants used the EyeCane visual-to-auditory navigation aid for non-visual navigation.\n\nWe found that retinotopic regions, including both dorsal stream regions (e.g. V6) and primary regions (e.g. peripheral V1), were selectively recruited for non-visual navigation only after the participants mastered the EyeCane demonstrating rapid plasticity for non-visual navigation. The hippocampus, considered the navigation networks core, displayed negative BOLD in all groups.\n\nOur results demonstrate the robustness of the retinotopic nodes modality-independent spatial role in non-visual human navigation to lifelong visual-deprivation, demonstrating that visual input during development is not required for their recruitment. Furthermore, our results with the blindfolded group demonstrate this recruitments robustness even to brief blindfolding, but only after brief training, demonstrating rapid task based plasticity. These results generalize the wider framework of task-selectivity rather than input-modality as a brain organization principle to dorsal-stream retinotopic areas and even for the first time to the primary visual cortex.\n\nHighlightsO_LIBoth visual and non-visual navigation recruit retinotopic regions\nC_LIO_LIAfter training blindfolded subjects selectively recruit V1 & V6 for navigation\nC_LIO_LIThis holds also for participants with no visual experience (congenitally blind)\nC_LIO_LIThe medial temporal lobe showed non-selective Negative BOLD in all groups\nC_LI\n\nDeclaration of interestsAll authors declare that they have no conflicts of interests.

neuroscience↗