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In asymmetric hearing loss (AHL), the normal pattern of contralateral hemispheric dominance for monaural stimulation is modified, with a shift towards the hemisphere ipsilateral to the better ear. The extent of this shift has been shown to relate to sound localization deficits. In this study, we examined whether cochlear implantation to treat postlingual AHL can restore the normal functional pattern of auditory cortical activity and whether this relates to improved sound localization. The auditory cortical activity was found to be lower in the AHL cochlear implanted (AHL-CI) participants. A cortical asymmetry index was calculated and showed that a normal contralateral dominance was restored in the AHL-CI patients for the nonimplanted ear, but not for the ear with the cochlear implant. It was found that the contralateral dominance for the nonimplanted ear strongly correlated with sound localization performance (rho = 0.8, P

Prader–Willi syndrome is a rare neurodevelopmental genetic disorder characterized by various endocrine, cognitive and behavioural problems. The symptoms include an obsession for food and reduced satiety, which leads to hyperphagia and morbid obesity. Neuropsychological studies have reported that Prader–Willi patients display altered social interactions with a specific weakness in interpreting social information and responding to them, a symptom close to that observed in autism spectrum disorders. In the present case-control study, we hypothesized that brain regions associated with compulsive eating behaviour would be abnormally activated by food-related odours in Prader–Willi syndrome, as these can stimulate the appetite and induce hunger-related behaviour. We conducted a brain imaging study using the olfactory modality because odours have a high-hedonic valence and can cause stronger emotional reactions than other modalities. Further, the olfactory system is also intimately associated with the endocrine regulation of energy balance and is the most appropriate modality for studies of Prader–Willi syndrome. A total of 16 Prader–Willi participants were recruited for this study, which is a significant achievement given the low incidence rate of this rare disease. The second group of 11 control age-matched subjects also participated in the brain imaging study. In the MRI scanner, using an MRI-compatible olfactometer during 56 block sessions, we randomly presented two odours (tulip and caramel), which have different hedonic valence and a different capacity to arouse hunger-related behaviour. Our results demonstrate that Prader–Willi participants have abnormal activity in the brain reward system that regulates eating behaviour. Indeed, we found that these patients had right amygdala activity up to five times higher in response to a food odour (caramel) compared with the tulip odour. In contrast, age-matched control participants had similar activity levels in response to both odours. The amygdala activity levels were found to be associated with the severity of the hyperphagia in Prader–Willi patients. Our results provide evidence for functional alteration of the right amygdala in Prader–Willi syndrome, which is part of the brain network involved in food addiction modulated by the ghrelin and oxytocin systems, which may drive the hyperphagia. Our study provides important new insights into the functioning of emotion-related brain circuits and pathology, and it is one of the few to explore the dysfunction of the neural circuits involved in emotion and addiction in Prader–Willi syndrome. It suggests new directions for the exploration and remediation of addictive behaviours.

Unilateral hearing loss (UHL) alters binaural cues affecting speech comprehension and sound localisation. While many patients with UHL perform poorly on binaural tasks, some are able to adapt to monaural deficit. We aimed to identify patients with UHL who use compensatory strategies and to explore the neural correlates of this adaptation using Mismatch Negativity (MMN). We recruited 21 patients with UHL and we separated them into three groups using cluster analysis based on measures of binaural processing. The resulting groups were referred to as the better, moderate and poorer performers clusters (BPC, MPC and PPC). We measured the MMN elicited by deviant sounds located 10°, 20° or 100° away from a standard sound. We found that the BPC group had a significant MMN for all three deviant sounds, as in a group of normal-hearing controls. In contrast, the PPC group and normal-hearing controls with an earplug did not have a significant MMN for the 10° and 20° deviations. For the 100° deviation, the scalp distribution was found to be maximal over central regions in the BPC group, while the PPC group showed a more frontal distribution. Differences were also found for the N100 evoked by standard sounds, with the BPC group showing a contralateral pattern of activation, as in the controls, and the PPC group showing more symmetrical hemispheric activation. These results indicate that patients with UHL can develop adaptive strategies that are reflected by sound processing differences at the cortical level.

Cochlear implanted (CI) adults with acquired deafness are known to depend on multisensory integration skills (MSI) for speech comprehension through the fusion of speech reading skills and their deficient auditory perception. But, little is known on how CI patients perceive prosodic information relating to speech content. Our study aimed to identify how CI patients use MSI between visual and auditory information to process paralinguistic prosodic information of multimodal speech and the visual strategies employed. A psychophysics assessment was developed, in which CI patients and hearing controls (NH) had to distinguish between a question and a statement. The controls were separated into two age groups (young and aged-matched) to dissociate any effect of aging. In addition, the oculomotor strategies used when facing a speaker in this prosodic decision task were recorded using an eye-tracking device and compared to controls. This study confirmed that prosodic processing is multisensory but it revealed that CI patients showed significant supra-normal audiovisual integration for prosodic information compared to hearing controls irrespective of age. This study clearly showed that CI patients had a visuo-auditory gain more than 3 times larger than that observed in hearing controls. Furthermore, CI participants performed better in the visuo-auditory situation through a specific oculomotor exploration of the face as they significantly fixate the mouth region more than young NH participants who fixate the eyes, whereas the aged-matched controls presented an intermediate exploration pattern equally reported between the eyes and mouth. To conclude, our study demonstrated that CI patients have supra-normal skills MSI when integrating visual and auditory linguistic prosodic information, and a specific adaptive strategy developed as it participates directly in speech content comprehension.

Spatial integration during the brain's cognitive activity prompts changes in energy used by different neuroglial populations. Nevertheless, the organisation of such integration in 3D -brain activity remains undescribed from a quantitative standpoint. In response, we applied a cross-correlation between brain activity and integrative models, which yielded a deeper understanding of information integration in functional brain mapping. We analysed four datasets obtained via fundamentally different neuroimaging techniques (functional magnetic resonance imaging [fMRI] and positron emission tomography [PET]) and found that models of spatial integration with an increasing input to each step of integration were significantly more correlated with brain activity than models with a constant input to each step of integration. In addition, marking the voxels with the maximal correlation, we found exceptionally high intersubject consistency with the initial brain activity at the peaks. Our method demonstrated for the first time that the network of peaks of brain activity is organised strictly according to the models of spatial integration independent of neuroimaging techniques. The highest correlation with models integrating an increasing at each step input suggests that brain activity reflects a network of integrative processes where the results of integration in some neuroglial populations serve as an input to other neuroglial populations.

Permanently changed sensory stimulation can modify functional connectivity patterns in the healthy brain and in pathology. In the pathology case, these adaptive modifications of the brain are referred to as compensation, and the subsequent configurations of functional connectivity are called compensatory plasticity. The variability and extent of auditory deficits due to the impairments in the hearing system determine the related brain reorganization and rehabilitation. In this review, we consider cross-modal and intra-modal brain plasticity related to bilateral and unilateral hearing loss and their restoration using cochlear implantation . Cross-modal brain plasticity may have both beneficial and detrimental effects on hearing disorders. It has a beneficial effect when it serves to improve a patient's adaptation to the visuo-auditory environment. However, the occupation of the auditory cortex by visual functions may be a negative factor for the restoration of hearing with cochlear implants . In what concerns intra-modal plasticity, the loss of interhemispheric asymmetry in asymmetric hearing loss is deleterious for the auditory spatial localization. Research on brain plasticity in hearing disorders can advance our understanding of brain plasticity and improve the rehabilitation of the patients using prognostic, evidence-based approaches from cognitive neuroscience combined with post-rehabilitation objective biomarkers of this plasticity utilizing neuroimaging.

We created a volumetric template of the marmoset (Callithrix jacchus) brain, which enables localization of the cortical areas defined in the Paxinos et al. (The marmoset brain in stereotaxic coordinates. Elsevier Academic Press, Cambridge, 2012) marmoset brain atlas, as well as seven broader cortical regions (occipital, temporal, parietal, prefrontal, motor, limbic, insular), different brain compartments (white matter, gray matter, cerebro-spinal fluid including ventricular spaces), and various other structures (brain stem, cerebellum, olfactory bulb, hippocampus). The template was designed from T1-weighted MR images acquired using a 3 T MRI scanner. It was based on a single fully segmented marmoset brain image, which was transported onto the mean of 13 adult marmoset brain images using a diffeomorphic strategy that fully preserves the brain topology. In addition, we offer an automatic segmentation pipeline which fully exploits the proposed template. The segmentation pipeline was quantitatively assessed by comparing the results of manual and automated segmentations. An associated program, written in Python, can be used from a command-line interface, or used interactively as a module of the 3DSlicer software. This program can be applied to the analysis of multimodal images, to map specific cortical areas in lesions or to define the seeds for further tractography analyses.

International audience; Auditory categorization is an important process in the perception and understanding of everyday sounds. The use of cochlear implants (CIs) may affect auditory categorization and result in poor abilities. The current study was designed to compare how children with normal hearing (NH) and children with CIs categorize a set of everyday sounds. We tested 24 NH children and 24 children with CI on a free-sorting task of 18 everyday sounds corresponding to four a priori categories: nonlinguistic human vocalizations, environmental sounds, musical sounds, and animal vocalizations. Multiple correspondence analysis revealed considerable variation within both groups of child listeners, although the human vocalizations and musical sounds were similarly categorized. In contrast to NH children, children with CIs categorized some sounds according to their acoustic content rather than their associated semantic information. These results show that despite identification deficits, children with CIs are able to categorize environmental and vocal sounds in a similar way to NH children, and are able to use categorization as an adaptive process when dealing with everyday sounds. When an infant is identified as having profound-to-total bilateral hearing loss, the surgical implantation of coch-lear implants (CIs) is envisaged as a means of restoring his or her access to auditory information. The benefits of CIs for speech perception in children with prelingual hearing loss have been widely documented over the past three decades, resulting in an extension of prescription criteria 1,2. One of the greatest proven benefits of CIs is speech comprehension 3,4. Alongside improvements in oral language skills, speech comprehension is seen as one of the key objectives of rehabilitation with CIs. A CI does not function in the same manner as a conventional hearing aid (i.e., by contributing to the amplification of sounds). Instead, it turns sounds into trains of electrical pulses that directly stimulate the auditory nerve. This information is then relayed to the auditory centres of the brain, which in turn transform the impulses into auditory percepts. However, the auditory information provided by the implant is spectrally degraded 5 and lacks the fine spectrotemporal information that is crucial to certain aspects of speech comprehension-most notably the perception of prosodic information 6-9. This means that other aspects of auditory perception are also problematic for CI users, such as the identification and recognition of environmental and musical sounds. Development of nonlinguistic sound perception The recovery and/or development of speech comprehension is normally seen as the main goal of CI implantation. Accordingly, only limited attention has been paid to the perception of nonlinguistic sounds in CI users. For example, whilst CIs may enhance users' awareness of their immediate auditory environment 10 , a substantial deficit remains in the perception and identification of specific environmental sounds 11-13 , that is, those not classified as speech or music. This deficit has a negative impact on how CI users interact with their environment, and it is therefore important for more studies to be conducted on this topic. To our knowledge, the identification of nonlinguistic sounds by implanted adults with postlingual deafness has only been reported in a small number of studies 11-15. There have been even fewer studies among children with CIs 16,17. Furthermore, owing to a lack of standardized protocols for assessing auditory performance and the use of different evaluation procedures (open-set or closed-set identification assessments, written words or images

International audience; Unilateral hearing loss (UHL) generates a disruption of binaural hearing mechanisms, which impairs sound localization and speech understanding in noisy environments. We conducted an original study using fMRI and psychoacoustic assessments to investigate the relationships between the extent of cortical reorganization across the auditory areas for UHL patients, the severity of unilateral hearing loss, and the deficit in binaural abilities. Twenty-eight volunteers (14 UHL patients) were recruited (twenty-two females and six males). The brain imaging analysis demonstrated that UHL induces a shift in aural dominance favoring the better ear, with a cortical reorganization located in the non-primary auditory areas, ipsilateral (same side) to the better ear. This reorganization is correlated not only to the hearing loss severity but also to spatial localization abilities. A regression analysis between brain activity and patient's performance clearly showed that the spatial hearing deficit was linked to a functional alteration of the posterior auditory areas known to process spatial hearing. Altogether, our study reveals that UHL alters the dorsal auditory stream, which is deleterious to spatial hearing.

Modern neuroimaging represents three-dimensional brain activity, which varies across brain regions. It remains unknown whether activity within brain regions is organized in spatial configurations to reflect perceptual and cognitive processes. We developed a rotational cross-correlation method allowing a straightforward analysis of spatial activity patterns for the precise detection of the spatially correlated distributions of brain activity. Using several statistical approaches, we found that the seed patterns in the fusiform face area were robustly correlated to brain regions involved in face-specific representations. These regions differed from the non-specific visual network meaning that activity structure in the brain is locally preserved in stimulation-specific regions. Our findings indicate spatially correlated perceptual representations in cerebral activity and suggest that the 3D coding of the processed information is organized in locally preserved activity patterns. More generally, our results provide the first demonstration that information is represented and transmitted as local spatial configurations of brain activity.

Prader-Willi syndrome (PWS) is a rare neurodevelopmental and genetic disorder that is characterized by various expression of endocrine, cognitive and behavioral problems, among which a true obsession for food and a deficit of satiety that leads to hyperphagia and severe obesity. Neuropsychological studies have reported that PWS display altered social interactions with a specific weakness in interpreting social information and in responding to them, a symptom closed to that observed in autism spectrum disorders (ASD). Based on the hypothesis that atypical multisensory integration such as face and voice interactions would contribute in PWS to social impairment we investigate the abilities of PWS to process communication signals including the human voice. Patients with PWS recruited from the national reference center for PWS performed a simple detection task of stimuli presented in an uni-o or bimodal condition, as well as a voice discrimination task. Compared to control typically developing (TD) individuals, PWS present a specific deficit in discriminating human voices from environmental sounds. Further, PWS present a much lower multisensory benefits with an absence of violation of the race model indicating that multisensory information do not converge and interact prior to the initiation of the behavioral response. All the deficits observed in PWS were stronger for the subgroup of patients suffering from Uniparental Disomy, a population known to be more sensitive to ASD. Altogether, our study suggests that the deficits in social behavior observed in PWS derive at least partly from an impairment in deciphering the social information carried by voice signals, face signals, and the combination of both. In addition, our work is in agreement with the brain imaging studies revealing an alteration in PWS of the "social brain network" including the STS region involved in processing human voices.

International audience; Modern neuroimaging represents three-dimensional brain activity, which varies across brain regions. It remains unknown whether activity of different brain regions has similar spatial organization to reflect similar cognitive processes. We developed a rotational cross-correlation method allowing a straightforward analysis of spatial activity patterns distributed across the brain in stimulation specific contrast images. Results of this method were verified using several statistical approaches on real and simulated random datasets. We found, for example, that the seed patterns in the fusiform face area were robustly correlated to brain regions involved in face-specific representations. These regions differed from the non-specific visual network meaning that activity structure in the brain is locally preserved in stimulus-specific regions. Our findings indicate spatially correlated perceptual representations in cerebral activity and suggest that the 3D coding of the processed information is organized using locally preserved activity patterns across the brain. More generally, our results demonstrate that information is represented and shared in the local spatial configurations of brain activity.

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It has been demonstrated in earlier studies that patients with a cochlear implant have increased abilities for audio-visual integration because the crude information transmitted by the cochlear implant requires the persistent use of the complementary speech information from the visual channel. The brain network for these abilities needs to be clarified. We used an independent components analysis (ICA) of the activation (H2(15)O) positron emission tomography data to explore occipito-temporal brain activity in post-lingually deaf patients with unilaterally implanted cochlear implants at several months post-implantation (T1), shortly after implantation (T0) and in normal hearing controls. In between-group analysis, patients at T1 had greater blood flow in the left middle temporal cortex as compared with T0 and normal hearing controls. In within-group analysis, patients at T0 had a task-related ICA component in the visual cortex, and patients at T1 had one task-related ICA component in the left middle temporal cortex and the other in the visual cortex. The time courses of temporal and visual activities during the positron emission tomography examination at T1 were highly correlated, meaning that synchronized integrative activity occurred. The greater involvement of the visual cortex and its close coupling with the temporal cortex at T1 confirm the importance of audio-visual integration in more experienced cochlear implant subjects at the cortical level.

We evaluated the relationship between binaural hearing deficits and quality of life. The study included 49 adults with asymmetric hearing loss (AHL), and 11 adult normal-hearing listeners (NHL) served as controls. Speech reception thresholds (SRT) were assessed with the French Matrix Test. Quality of life was evaluated with the Speech, Spatial and Qualities of Hearing Scale (SSQ) and the Glasgow Health Status Inventory. Speech recognition in noise was significantly poorer for AHL subjects [-0.12 dB signal-to-noise ratio (SNR) in dichotic (with speech presented to the poorer ear and noise to the better ear), -1.72 dB in diotic and -6.84 dB in reverse-dichotic conditions] compared to NHL (-4.98 dB in diotic and -9.58 dB in dichotic conditions). Scores for quality-of-life questionnaires were significantly below norms. Significant correlations were found between the SRT for the dichotic condition and the SSQ total score (r = -0.38, p = 0.01), and pure-tone average thresholds for both groups.

We investigated speech recognition in noise in subjects with mild to profound levels of unilateral hearing loss. Thirty-five adults were evaluated using an adaptive signal-to-noise ratio (SNR50) sentence recognition threshold test in three spatial configurations. The results revealed a significant correlation between pure-tone average audiometric thresholds in the poorer ear and SNR thresholds in the two conditions where speech and noise were spatially separated: dichotic - with speech presented to the poorer ear and reverse dichotic - with speech presented to the better ear. This first result suggested that standard pure-tone air-conduction thresholds can be a reliable predictor of speech recognition in noise for binaural conditions. However, a subgroup of 14 subjects was found to have poorer-than-expected speech recognition scores, especially in the reverse dichotic listening condition. In this subgroup 9 subjects had been diagnosed with vestibular schwannoma at stage III or IV likely affecting the lower brainstem function. These subjects showed SNR thresholds in the reverse dichotic condition on average 4dB poorer (higher) than for the other 21 normally-performing subjects. For the 7 of 9 subjects whose vestibular schwannoma was removed, the deficit was no longer apparent on average 5 months following the surgical procedure. These results suggest that following unilateral hearing loss the capacity to use monaural spectral information is supported by the lower brainstem.

In classical neuroimaging, the activity of each voxel is considered separately. However, it was recently demonstrated that there are significant stimulation-specific differences between adjacent voxels at the group level. With this approach, the activity of adjacent voxels in the same condition is compared, and the direction of the highest increase of activity in the neighbourhood of each voxel is established as a gradient vector per voxel. Using this vector approach, we compared fMRI, EEG and MEG spatial differential activity during different tasks to see what amount of fMRI differential activity corresponds to the electromagnetic differential activity. Distributed source reconstruction was used to obtain 3-dimensional models of electric and magnetic activity in EEG and MEG prior to vector analysis. Using independent datasets, we illustrated that the mean overlap of the fMRI differential activity with EEG and MEG is 79%. In addition, about 93% of divergence (spatial sources) in fMRI corresponded to the EEG and MEG divergences. These results correspond to the spatial sum of the peak activities in EEG and MEG and, further, suggest a link between the spatial and temporal properties of brain activity. We propose a novel model of activity flows in the brain to explain this link.

International audience; Due to signal distortion, speech comprehension in cochlear-implanted (CI) patients relies strongly on visual information, a compensatory strategy supported by important cortical crossmodal reorganisations. Though crossmodal interactions are evident for speech processing, it is unclear whether a visual influence is observed in CI patients during non-linguistic visual-auditory processing, such as face-voice interactions, which are important in social communication. We analyse and compare visual-auditory interactions in CI patients and normal-hearing subjects (NHS) at equivalent auditory performance levels. Proficient CI patients and NHS performed a voice-gender categorisation in the visual-auditory modality from a morphing-generated voice continuum between male and female speakers, while ignoring the presentation of a male or female visual face. Our data show that during the face-voice interaction, CI deaf patients are strongly influenced by visual information when performing an auditory gender categorization task, in spite of maximum recovery of auditory speech. No such effect is observed in NHS, even in situations of CI simulation. Our hypothesis is that the functional crossmodal reorganisation that occurs in deafness could influence nonverbal processing, such as face-voice interaction; this is important for patient internal supramodal representation.

International audience; In this review, we discuss evidence from our recent studies and the literature that deaf patients after cochlear implantation partly rely on visual cues during auditory recovery and develop mechanisms of audio-visual integration as a strategy to maintain high levels of speech recognition in the noisy auditory environments provided by cochlear implants. This evidence is considered both at the behavioural level and at the level of cortical activity as explored by studies in functional neuroimaging. Since coupling different modalities facilitates perceptual learning in a single modality, we believe that a strong visually and audio-visually based rehabilitation during the first months after cochlear implantation would significantly improve and hasten the functional recovery of speech intelligibility and other auditory functions in these patients.

International audience; In functional neuroimaging studies, task-related activity refers to the signal difference between the stimulation and rest conditions. We asked whether long-term changes in the sensory environment may affect brain activity at rest. To answer this question, we compared regional cerebral blood flow between a group of normally hearing controls and a group of cochlear-implanted (CI) deaf patients. Here we present evidence that long-term alteration of auditory experience, such as profound deafness followed by partial auditory recuperation through cochlear implantation, leads to functional cortical reorganizations at rest. Without any visual or auditory stimulation, CI subjects showed changes of cerebral blood flow in the visual, auditory cortex, Broca area, and in the posterior temporal cortex with an increment of activity in these areas from the time of activation of the implant to less than a year after the implantation.

The number of studies that use the common marmoset (Callithrix jacchus) in various fields of neurosciences is increasing dramatically. In general, animals enter the study when their health status is considered satisfactory on the basis of classical clinical investigations. In behavioral studies, variations of score between individuals are frequently observed, some of them being considered as poor performers or outliers. Experimenters rarely consider the fact that it could be related to some brain anomaly. This raises the important issue of the reliability of such classical behavioral approaches without using complementary imaging, especially in animals lacking striking external clinical signs. Here we report the case of a young marmoset which presented a set of cognitive impairments in two different tasks compared to other age-matched animals. Brain imaging revealed a patent right lateral ventricular enlargement with a mild hippocampal atrophy. This abnormality could explain the cognitive impairments of this animal. Such a case points to the importance of complementing behavioral studies by imaging explorations to avoid experimental bias.

Syntactic processing of spoken speech often involves prosodic clues processing. In the present PET and ERP study, subjects listened to phrases in which different prosodic segmentation dramatically changed the meaning of the phrase. In the contrast of segmented vs. non-segmented phrases, PET data revealed activation in the right dorsolateral prefrontal cortex and in the right cerebellum. These brain structures, therefore, might be part of the syntactic analysis network involved in prosodic segmentation and pitch processing. ERP results revealed frontal negativity that was sensitive to the position of the segmenting pause, possibly reflecting prosody-based semantic prediction. The present results are discussed in the context of their relation to brain networks of emotions, prosody, and syntax perception.

It was shown recently in neuroimaging that spatial differentiation of brain activity provides novel information about brain function. This confirms the integrative organisation of brain activity, but given present technical limitations of neuroimaging approaches, the exact role of integrative activity remains unclear. We trained a neural network to integrate information using random numbers so as to imitate the “centre-periphery” pattern of brain activity in neuroimaging. Only the hierarchical organisation of the network permitted the learning of fast and reliable integration. We presented images to the trained network and, by spatial differentiation of the network activity, obtained virtual spaces with the presented images. Thus, our study established the necessity of the hierarchical organisation of neural networks for integration and demonstrated that the role of neural integration in the brain may be to create virtual spaces with internal representations of the objects.

Modern cochlear implantation technologies allow deaf patients to understand auditory speech; however, the implants deliver only a coarse auditory input and patients must use long-term adaptive processes to achieve coherent percepts. In adults with post-lingual deafness, the high progress of speech recovery is observed during the first year after cochlear implantation, but there is a large range of variability in the level of cochlear implant outcomes and the temporal evolution of recovery. It has been proposed that when profoundly deaf subjects receive a cochlear implant, the visual cross-modal reorganization of the brain is deleterious for auditory speech recovery. We tested this hypothesis in post-lingually deaf adults by analysing whether brain activity shortly after implantation correlated with the level of auditory recovery 6 months later. Based on brain activity induced by a speech-processing task, we found strong positive correlations in areas outside the auditory cortex. The highest positive correlations were found in the occipital cortex involved in visual processing, as well as in the posterior-temporal cortex known for audio-visual integration. The other area, which positively correlated with auditory speech recovery, was localized in the left inferior frontal area known for speech processing. Our results demonstrate that the visual modality's functional level is related to the proficiency level of auditory recovery. Based on the positive correlation of visual activity with auditory speech recovery, we suggest that visual modality may facilitate the perception of the word's auditory counterpart in communicative situations. The link demonstrated between visual activity and auditory speech perception indicates that visuoauditory synergy is crucial for cross-modal plasticity and fostering speech-comprehension recovery in adult cochlear-implanted deaf patients.

International audience; : It was recently shown that brain activity can be represented as a stimulation-specific vector field. Since the vector field of brain activity is specifically transformed by sensory input, we suggested that a tensor field that transforms brain activity reflects sensory input. We calculated the tensor fields that transform brain activity between visual baseline and auditory word processing in PET data and between environmental sounds and auditory word processing in fMRI data. In the first comparison, significant clusters formed a distributed network over the brain cortex. In the second comparison, clusters that were more localised in the temporo-frontal network of speech processing. Our study therefore demonstrated that tensor fields reflect the sensory input that specifically transforms brain activity.

The visual cues involved in auditory speech processing are not restricted to information from lip movements but also include head or chin gestures and facial expressions such as eyebrow movements. The fact that visual gestures precede the auditory signal implicates that visual information may influence the auditory activity. As visual stimuli are very close in time to the auditory information for audiovisual syllables, the cortical response to them usually overlaps with that for the auditory stimulation; the neural dynamics underlying the visual facilitation for continuous speech therefore remain unclear. In this study, we used a three-word phrase to study continuous speech processing. We presented video clips with even (without emphasis) phrases as the frequent stimuli and with one word visually emphasized by the speaker as the non-frequent stimuli. Negativity in the resulting ERPs was detected after the start of the emphasizing articulatory movements but before the auditory stimulus, a finding that was confirmed by the statistical comparisons of the audiovisual and visual stimulation. No such negativity was present in the control visual-only condition. The propagation of this negativity was observed between the visual and fronto-temporal electrodes. Thus, in continuous speech, the visual modality evokes predictive coding for the auditory speech, which is analysed by the cerebral cortex in the context of the phrase even before the arrival of the corresponding auditory signal.

International audience; HYPOTHESIS: : Bilateral stimulation through cochlear implants induces a brain activity pattern closer to the normal one than unilateral stimulation. BACKGROUND: : Although it has been shown that speech comprehension through bilateral cochlear implants leads to better performances than after unilateral implantation, the existence of neural underpinnings of this improvement remains to be studied. METHODS: : We performed an H2O positron emission tomographic study of word recognition in 5 patients with bilateral cochlear implants and 5 normal-hearing controls. Subjects had to distinguish words from nonwords in binaural and monaural conditions. RESULTS: : There was no overactivation in patients for binaural stimulation, with a hypoactivation in the right temporal cortex. For monaural stimulation, patients demonstrated more activation contralaterally to the stimulation side in the posterior temporal cortex and in the cerebellum. CONCLUSION: : Binaural stimulation through cochlear implants is advantageous compared with the monaural at the neurofunctional level because the pattern of brain activity is closer to the normal one.

International audience; Studies using event related potentials have shown that men are more likely than women to rely on semantic cues when understanding emotional speech. In a previous functional Magnetic Resonance Imaging (fMRI) study, using an affective sentence classification task, we were able to separate areas involved in semantic processing and areas involved in the processing of affective prosody (Beaucousin et al., 2007). Here we searched for sex-related differences in the neural networks active during emotional speech processing in groups of men and women. The ortholinguistic abilities of the participants did not differ when evaluated with a large battery of tests. Although the neural networks engaged by men and women during emotional sentence classification were largely overlapping, sex-dependent modulations were detected during emotional sentence classification, but not during grammatical sentence classification. Greater activity was observed in men, compared with women, in inferior frontal cortical areas involved in emotional labeling and in attentional areas. In conclusion, at equivalent linguistic abilities and performances, men activate semantic and attentional cortical areas to a larger extent than women during emotional speech processing.

Background Degrading speech through an electronic synthesis technique called vocoding has been shown to affect cerebral processing of speech in several cortical areas. However, it is not clear whether the effects of speech degradation by vocoding are related to acoustical degradation or by the associated loss in intelligibility. Using vocoding and a parametric variation of the number of frequency bands used for the encoding, we investigated the effects of the degradation of auditory spectral content on cerebral processing of intelligible speech (words), unintelligible speech (words in a foreign language), and complex environmental sounds. Results Vocoding was found to decrease activity to a comparable degree for intelligible and unintelligible speech in most of the temporal lobe. Only the bilateral posterior temporal areas showed a significant interaction between vocoding and intelligibility, with a stronger vocoding-induced decrease in activity for intelligible speech. Comparisons to responses elicited by environmental sounds showed that portions of the temporal voice areas (TVA) retained their greater responses to voice even under adverse listening conditions. The recruitment of specific networks in temporal regions during exposure to degraded speech follows a radial and anterior-posterior topography compared to the networks recruited by exposure to speech that is not degraded. Conclusions Different brain networks are involved in vocoded sound processing of intelligible speech, unintelligible speech, and non-vocal sounds. The greatest differences are between speech and environmental sounds, which could be related to the distinctive temporal structure of speech sounds.

International audience; The article aims to test the hypothesis that audiovisual integration can improve spatial hearing in monaural conditions when interaural difference cues are not available. We trained one group of subjects with an audiovisual task, where a flash was presented in parallel with the sound and another group in an auditory task, where only sound from different spatial locations was presented. To check whether the observed audiovisual effect was similar to feedback, the third group was trained using the visual feedback paradigm. Training sessions were administered once per day, for 5 days. The performance level in each group was compared for auditory only stimulation on the first and the last day of practice. Improvement after audiovisual training was several times higher than after auditory practice. The group trained with visual feedback demonstrated a different effect of training with the improvement smaller than the group with audiovisual training. We conclude that cross-modal facilitation is highly important to improve spatial hearing in monaural conditions and may be applied to the rehabilitation of patients with unilateral deafness and after unilateral cochlear implantation.

International audience; Speechreading is an important form of communicative activity that improves social adaptation in deaf adults. Cochlear implantation allows interaction between the visual speechreading abilities developed during deafness and the auditory sensory experiences acquired through use of the cochlear implant. Crude auditory information provided by the implant is analyzed in parallel with conjectural information from speechreading, thus creating new profiles of audiovisual integration with implications for brain plasticity. Understanding the peculiarities of change in speechreading after cochlear implantation may improve our understanding of brain plasticity and provide useful information for functional rehabilitation of implanted patients. In this article, we present a generalized review of our recent studies and indicate perspectives for further research in this domain.

International audience; We aimed to determine the effect of prosodic familiarity on automatic word processing in the brain by comparing the mismatch negativity (MMN) components of the event-related brain potential (ERP) elicited by words and pseudowords with familiar and unfamiliar stress patterns. The results show that the MMN was elicited by a change from unfamiliar to familiar words and a change from a familiar to an unfamiliar word-stress pattern.When familiar words were accompanied by an unfamiliar stress pattern, the MMN response was significantly delayed in comparison with the familiar words with a familiar stress pattern, suggesting that an unfamiliar prosodic pattern increased the computational needs in word recognition but did not prevent it. In addition to the effects of familiarity on the MMN, we found a positive brain response peaking between 100 and 200 ms that could be associated with the processing of familiar auditory objects. The present results expand the understanding of the early stages of speech processing in the human brain by demonstrating how automatic word processing is affected by prosodic cues that play an important role in the segmentation of continuous speech.

International audience; In this article, we consider the view on schizophrenia that asserts this disease originates from a deficit in the hemispheric specialization for language. We suggest that a deficit in the hemispheric specialization for language may be a consequence of the other recently shown neurophysiological deficit of schizophrenia, namely deviance detection. We hypothesise that a deficit of deviance detection related to the dysfunction of NMDA receptors in schizophrenia leads to the abnormal interaction between the parallel and sequential streams of speech processing in the brain. This hypothesis opens perspectives for genetic, molecular and pharmacological studies of the deficit of deviance detection in schizophrenia, as reflected by event-related potentials and neuroimaging during speech processing.

International audience; Several neuropsychological and neuroimaging studies on gender differences in speech processing lead to the suggestion that women use the neural network of predictive and integrative analysis of speech to a larger extent than men. During speech-reading there is indeed a lack of reliable clues for word recognition which should emphasize predictive and integrative strategies of the brain. Our study aimed to explore gender differences in deaf and cochlear implanted (CI) patients at different levels during speech-reading, for words or phonemes, that we consider, correspond to increased involvement of predictive and integrative analysis. We collected speech-reading scores in a control group of normally hearing subjects (n=42) and in a group of deaf patients - who are good speech-readers - tested before, early after and late after cochlear implantation (n=97). Patient groups were almost equally distributed between follow-up and new patients. In normally hearing controls, women speech-read words better than men. This difference was also observed in all patients but not in experienced cochlear implant users. We did not observe a gender difference during speech-reading of isolated phonemes neither for controls nor for patients. We conclude that the better speech-reading ability of women for words but not for phonemes is in line with their greater use of predictive and integrative strategies for speech processing. Furthermore, we observed a progressive cross-modal compensation in male CI users after cochlear implantation which suggests a synergetic perceptual facilitation involving the visual and the recovering auditory modalities. This could lead to an improved performance in both auditory and visual modalities, the latter being constantly recruited to complement the crude information provided by the implant. Altogether, our data provide insights into cross-modal compensation in the adult brain following sensory privation.

International audience; This article presents an activation–verification approach to the problem of continuous speech processing in the brain. The presented model consists of two streams of processing: sequential and parallel. The sequential stream is strictly modular; the parallel stream is highly interactive and creates predictive coding variants based on initially missing linguistic information. The parallel stream predictions are incrementally verified, accepted, or rejected on the basis of the actual linguistic information perceived by the sequential stream. In this model, the brain's continuous speech processing, regarded as a whole, remains uninterrupted due to the functioning of the parallel stream. We discuss the possible application of the model to the problem of hemispheric asymmetry as reflected by studies of brain lesions and functional neuroimaging.

International audience; There is increasing focus on the neurophysiological underpinnings of brain activations, giving birth to an emerging branch of neuroscience - neuroenergetics. However, no common definition of "brain activation" exists thus far. In this article, we define brain activation as the information-driven reorganization of energy flows in a population of neuroglial units that leads to an overall increase in energy utilization in this population. On the basis of this definition, the key aspects of modern biochemical and biophysical approaches to neuroenergetics are considered from the perspective of the links between these approaches within the context of the free energy minimization principle and the neurophysiological conception of deviance detection. In this light, we consider brain basal activity as subserving internal representations of the environment (predictive coding), and brain activation as reflecting the level of deviance from predictive coding.

International audience; This article aims to provide a theoretical framework to elucidate the neurophysiological underpinnings of deviance detection as reflected by mismatch negativity. A six-step model of the information processing necessary for deviance detection is proposed. In this model, predictive coding of learned regularities is realized by means of long-term potentiation with a crucial role for NMDA receptors. Mismatch negativity occurs at the last stage of the model, reflecting the increase in free energy associated with the switching on of silent synapses and the formation of new neural circuits required for adaptation to the environmental deviance. The model is discussed with regard to the pathological states most studied in relation to mismatch negativity: alcohol intoxication, alcohol withdrawal, and schizophrenia.

International audience