Search

This review intends to provide an overview of the current knowledge on neurologic sequelae of COVID-19 and their possible etiology, and, based on available data, proposes possible improvements in current medical care procedures. We conducted a thorough review of the scientific literature on neurologic manifestations of COVID-19, the neuroinvasive propensity of known coronaviruses (CoV) and their possible effects on brain structural and functional integrity. It appears that around one third of COVID-19 patients admitted to intensive care units (ICU) for respiratory difficulties exhibit neurologic symptoms. This may be due to progressive brain damage and dysfunction triggered by severe hypoxia and hypoxemia, heightened inflammation and SARS-CoV-2 dissemination into brain parenchyma, as suggested by current reports and analyses of previous CoV outbreaks. Viral invasion of the brain may particularly target and alter brainstem and thalamic functions and, consequently, result in sensorimotor dysfunctions and psychiatric disorders. Moreover, data collected from other structurally homologous CoV suggest that SARS-CoV-2 infection may lead to brain cell degeneration and demyelination similar to multiple sclerosis (MS). Hence, current evidence warrants further evaluation and long-term follow-up of possible neurologic sequelae in COVID-19 patients. It may be particularly relevant to evaluate brainstem integrity in recovered patients, as it is suspected that this cerebral area may particularly be dysfunctional following SARS-CoV-2 infection. Because CoV infection can potentially lead to chronic neuroinflammation and progressive demyelination, neuroimaging features and signs of MS may also be evaluated in the long term in recovered COVID-19 patients., Highlights • Acute neurologic symptoms are observed in one third of COVID-19 patients • Neurotropism of SARS-CoV-2 is highly suspected • Brainstem damage may be a crucial driver for COVID-19-associated respiratory failure • COVID-19 is likely to trigger demyelination similarly to multiple sclerosis • Monitoring patients using Auditory Brainstem Responses and neuroimaging is warranted

A reproducible method to measure the intelligibility of communication systems is required to assess their efficiency. The current study seeks to develop a French version of the Modified Rhyme Test (MRT) [(House, Williams, Heker, and Kryter (1965). J. Acoust. Soc. Am. 37, 158-66], an intelligibility test composed of 50 six-word lists, originally developed for military applications and now widely used. An evaluation of the authors' French MRT was carried out, reproducing the original experimental conditions used by House and colleagues. Very similar results were found between the original MRT and the French MRT, validating the latter for further use and dissemination.

Purpose: Misplacing or losing personal belongings is a concern of everyday life among people of all ages. Older adults with cognitive impairment are significantly more affected by this problem. It is a source of frustration, anxiety, interpersonal conflict and disability in this population. Informal caregivers are greatly impacted by this problem, which compels them to spend a lot of time searching for misplaced items and comforting the person. Assistive technology could thus be of great benefit in this area. However, existing item locator devices do not appear to meet the needs of older adults with cognitive disorders. The TROUVE project aims to conceive and assess an innovative item locator device that effectively addresses their needs, capacities, and goals. Procedure: The project team conducted a co-design process involving relevant stakeholders (persons with cognitive impairment, informal and formal caregivers, researchers, industry representatives, ethical bodies) using user-tests, focus groups, interviews, and questionnaires. The project plan involved three phases: (1) analysis of end-users' needs, (2) definition of system requirements and iterative prototype development, and (3) prototype assessment. Findings: The analysis of end users' needs and the evaluation of existing item locator devices provided us with details about the items which are the most frequently lost or misplaced by older adults at home and their coping strategies to manage these situations. The analysis of usability problems observed throughout the assessment of existing devices allowed the definition of the system requirements. Prototype assessment showed that spatialized sound can be used to help these users find missing items, and that an item locator device can be part of a more comprehensive assistive and rehabilitation system such as a robot. Conclusions: An item locator that relies on sensory information (spatialized sound) rather than on conceptual reasoning (“the item is located to your left 4 meters away”) appears to be an interesting solution to address the problem of misplacing personal items in elderly with cognitive impairment. Involving end-users and relevant stakeholders throughout the cycle of design and development of assistive technology is an effective method to explore design opportunities and define creative solutions.

The chapter aims at analyzing the impact of the levels of talkers and their spatial separation on the cognitive resources of the listeners. For this purpose, 14 young listeners were chosen to report the speech emitted by a target talker in the presence of a concurrent masker talker and results were recorded.

In a multi-talker situation, spatial separation between talkers reduces cognitive processing load: this is the “spatial release of cognitive load”. The present study investigated the role played by the relative levels of the talkers on this spatial release of cognitive load. During the experiment, participants had to report the speech emitted by a target talker in the presence of a concurrent masker talker. The spatial separation (0° and 120° angular distance in azimuth) and the relative levels of the talkers (adverse, intermediate, and favorable target-to-masker ratio) were manipulated. The cognitive load was assessed with a prefrontal functional near-infrared spectroscopy. Data from 14 young normal- hearing listeners revealed that the target-to-masker ratio had a direct impact on the spatial release of cognitive load. Spatial separation significantly reduced the prefrontal activity only for the intermediate target-to-masker ratio and had no effect on prefrontal activity for the favorable and the adverse target-to-masker ratios. Therefore, the relative levels of the talkers might be a key point to determine the spatial release of cognitive load and more specifically the prefrontal activity induced by spatial cues in multi- talker environments.

Human sound localization abilities rely on binaural and spectral cues. Spectral cues arise from interactions between the sound wave and the listener's body (head-related transfer function, HRTF). Large individual differences were reported in localization abilities, even in young normal-hearing adults. Several studies have attempted to determine whether localization abilities depend mostly on acoustical cues or on perceptual processes involved in the analysis of these cues. These studies have yielded inconsistent findings, which could result from methodological issues. In this study, we measured sound localization performance with normal and modified acoustical cues (i.e., with individual and non-individual HRTFs, respectively) in 20 naive listeners. Test conditions were chosen to address most methodological issues from past studies. Procedural training was provided prior to sound localization tests. The results showed no direct relationship between behavioral results and an acoustical metrics (spectral-shape prominence of individual HRTFs). Despite uncertainties due to technical issues with the normalization of the HRTFs, large acoustical differences between individual and non-individual HRTFs appeared to be needed to produce behavioral effects. A subset of 15 listeners then trained in the sound localization task with individual HRTFs. Training included either visual correct-answer feedback (for the test group) or no feedback (for the control group), and was assumed to elicit perceptual learning for the test group only. Few listeners from the control group, but most listeners from the test group, showed significant training-induced learning. For the test group, learning was related to pre-training performance (i.e., the poorer the pre-training performance, the greater the learning amount) and was retained after 1 month. The results are interpreted as being in favor of a larger contribution of perceptual factors than of acoustical factors to sound localization abilities with virtual sources.

Large individual differences are relatively common in human perception. Spatial hearing is not an exception; for instance, two listeners can perceive the same auditory target to be at very different spatial locations. Such variability cannot be considered as mere experimental noise but as true data that we have to use for explaining the mechanisms underlying the perception of auditory space. The 22 papers of this research topic explore individual differences in almost every aspect of auditory space perception.

The mammalian auditory system contains descending neural pathways, some of which project onto the cochlea via the medial olivocochlear (MOC) system. The function of this efferent auditory system is not entirely clear. Behavioral studies in animals with olivocochlear (OC) lesions suggest that the MOC serves to facilitate sound localization in noise. In the current work, noise-induced OC activity (the OC reflex) and sound-localization performance in noise were measured in normal-hearing humans. Consistent with earlier studies, both measures were found to vary substantially across individuals. Importantly, significant correlations were observed between OC-reflex strength and the effect of noise on sound-localization performance; the stronger the OC reflex, the less marked the effect of noise. These results suggest that MOC activation by noise helps to counteract the detrimental effects of background noise on neural representations of direction-dependent spectral features, which are especially important for accurate localization in the up/down and front/back dimensions.

The activity of the medial olivocochlear bundle (MOCB) can be studied in humans through variations in the level of evoked otoacoustic emissions (EOAEs) elicited by contralateral acoustic stimuli (CAS). The present study sought to investigate how the activity of the MOC system at a given frequency, as measured through the contralateral suppression of tone-pip EOAEs, depends on the bandwidth of the contralateral stimulus. EOAEs were recorded in 155 normal-hearing subjects, successively with and without contralateral stimuli whose bandwidth, center frequency and level were systematically varied. We showed a clear dependence of contralateral EOAE suppression on bandwidth demonstrating increased suppression with increased bandwidth over about two octaves around the center frequency of the noise. This effect was obtained irrespective of whether contralateral noise energy was kept constant independently of bandwidth or not, which indicates a role of bandwidth per se in contralateral EOAE suppression. Results are interpreted in terms of a simple model of MOCB activation mechanisms including peripheral bandpass filtering, within-channel compression and across-channel spatial summation by the afferent paths. Complementary experiments suggested a greater effectiveness of increases in bandwidth on the upper than on the lower side and of frequency components akin to or remote from the test frequency than of intermediate bands. Finally, these results were complemented by detailed spectrum analyses of the EOAE level variations induced by the different noises, which revealed that whilst noise components close to or remote from the center frequency generally attenuated EOAE level, intermediate components could in some cases lead to a relative increase in EOAE level. These results can further be explained by assuming different positive and negative weights on the inputs to the spatial summation process depending on their position relative to the center frequency.

Variations in the amplitude of transiently evoked otoacoustic emissions (TEOAEs) produced by a contralateral complex tone were measured in 26 normal-hearing human subjects. TEOAEs were evoked using a 1-kHz tone pip at 60 dB SPL. The contralateral complex consisted of harmonic components with frequencies between 400 and 2000 Hz; it was presented at levels ranging from 40 to 50 dB SL and its fundamental frequency (F0) was varied. In experiment 1, the dependence of TEOAE amplitude variations on the F0 of the contralateral complex was measured by varying the F0 from 50 to 400 Hz in octave steps. The results revealed a nonmonotonic dependence of TEOAE amplitude variations on contralateral F0, with significantly larger TEOAE suppression for F0's of 100 and 200 Hz than for F0's of 50 and 400 Hz. Experiment 2, in which the harmonics were summed in alternating sine-cosine phase instead of constant sine phase, showed a shift of the function relating TEOAE attenuation to F0 towards lower F0's, indicating that the waveform repetition rate, rather than harmonic spacing, was the actual factor of the dependence of contralateral TEOAE attenuation on F0. Furthermore, significantly smaller suppression was observed with the alternating-phase complexes than with the sine-phase complexes, suggesting an influence of the waveform crest factor. Experiment 3 showed no difference between the contralateral TEOAE attenuation effects produced by positive and negative Schroeder-phase complexes. Overall, these results bring further arguments for the notion that contralaterally induced medial olivocochlear bundle (MOCB) activity, as measured through the contralateral suppression of TEOAEs in humans, is sensitive to the rate of temporal envelope fluctuations of the contralateral stimulus, with preferential rates around 100-200 Hz.

Pure tone audiometry is the main method used to monitor the hearing of French military personnel. However, the link between hearing ability in a real environment and pure tone audiometry has been questioned. Previous studies have reported significant variability in speech understanding in noise among young normal-hearing individuals. This inter-individual variability could be explained by the fact that high noise levels exposure would lead to the development of cochlear synaptopathies without causing a permanent rise in audiometric thresholds. Therefore, pure tone audiometry conducted at the periodic medical check-up could be doubly limited: on the one hand as a secondary prevention measure and on the other hand as a measure of hearing ability. To assess whether pure tone audiometry is sufficient to predict speech understanding in noise in military personnel regularly exposed to noise, and to provide evidence for the existence of cochlear synaptopathies in humans, we performed pure tone audiometry and speech audiometry in noise, in 65 soldiers. They all had an occupational noise exposure, and their risk of cochlear synaptopathy was estimated according to their level of noise exposure and their age. Our results show a lack of correlation between the thresholds measured in pure tone audiometry and the score in speech audiometry in noise. Furthermore, the results of speech audiometry in noise do not deteriorate more rapidly with age in the most noise-exposed population, possibly because of different individual susceptibility. Longitudinal studies considering the many confounding factors, including individual susceptibility, will be needed to demonstrate cochlear synaptopathy in the military population. Our results suggest that periodic voice audiometry in noise could improve the monitoring of hearing in military personnel.; L’audiométrie tonale est prépondérante dans le suivi auditif des militaires français. Le lien entre capacité auditive en environnement réel et audiométrie tonale est pourtant remis en question. De précédentes études ont observé une importante variabilité dans les compréhensions de parole dans le bruit parmi de jeunes normo-entendants. Cette variabilité inter-individuelle pourrait être expliquée par le fait qu’une exposition à de forts niveaux de bruit entraîne l’apparition de synaptopathies cochléaires sans provoquer d’élévation permanente des seuils audiométriques. Ainsi, l’audiométrie tonale réalisée en visite médicale périodique pourrait être doublement limitée : d’une part en tant que mesure de prévention secondaire et d’autre part en tant que mesure des capacités auditives. Pour évaluer si l’audiométrie tonale suffit à prédire la compréhension de la parole dans le bruit de militaires exposés régulièrement au bruit, et apporter des arguments sur l’existence des synaptopathies cochléaires chez l’humain, nous avons réalisés une audiométrie tonale et une audiométrie vocale dans le bruit, chez 65 militaires. Ils étaient exposés professionnellement au bruit et leur risque de synaptopathie cochléaire était estimé selon leur niveau d’exposition au bruit et leur âge. Nos résultats montrent une absence de corrélation entre les seuils mesurés en audiométrie tonale et le score en audiométrie vocale dans le bruit. Par ailleurs, les résultats en audiométrie vocale dans le bruit ne se dégradent pas plus vite avec l’âge chez les personnes les plus exposées au bruit, peut-être du fait de susceptibilité individuelle différente. Des études longitudinales prenant compte des nombreux facteurs confondants dont la susceptibilité individuelle seront nécessaires pour mettre en évidence la synaptopathie cochléaire en population militaire. Nos résultats suggèrent que la réalisation périodique d’audiométries vocales dans le bruit pourrait améliorer le suivi de l’audition des militaires.