How environmental sounds become meaningful

The term "sound object" describes an auditory experience that is associated with an acoustic event produced by a sound source. In natural settings, a sound produced by a living being or an object provides information about the identity and the location of the sound source. Sound's identity is orocessed alono the ventral "What" pathway which consists of regions within the superior and middle temporal cortices as well as the inferior frontal gyrus. This work concerns the creation of individual auditory object representations in narrow semantic categories and their plasticity using electrical imaging. Discrimination of sounds from broad category has been shown to occur along a temporal hierarchy and in different brain regions along the ventral "What" pathway. However, sounds belonging to the same semantic category, such as faces or voices, were shown to be discriminated in specific brain areas and are thought to represent a special class of stimuli. I have investigated how cortical representations of a narrow category, here birdsongs, is modulated by training novices to recognized songs of individual bird species. Dynamic analysis of distributed source estimations revealed differential sound object representations within the auditory ventral "What" pathway as a function of the level of expertise newly acquired. Correct recognition of trained items induces a sharpening within a left-lateralized semantic network starting around 200ms, whereas untrained items' processing occurs later in lower-level and memory-related regions. With another category of sounds belonging to the same category, here heartbeats, I investigated the cortical representations of correct and incorrect recognition of sounds. Source estimations revealed differential representations partially overlapping with regions involved in the semantic network that is activated when participants became experts in the task. Incorrect recognition also induces a higher activation when compared to correct recognition in regions processing lower-level features. The discrimination of heartbeat sounds is a difficult task and requires a continuous listening. I investigated whether the repetition effects are modulated by participants' behavioral performance. Dynamic source estimations revealed repetition suppression in areas located outside of the semantic network. Therefore, individual environmental sounds become meaningful with training. Their representations mainly involve a left-lateralized network of brain regions that are tuned with expertise, as well as other brain areas, not related to semantic processing, and occurring in early stages of semantic processing. -- Le terme objet sonore" décrit une expérience auditive associée à un événement acoustique produit par une source sonore. Dans l'environnement, un son produit par un être vivant ou un objet fournit des informations concernant l'identité et la localisation de la source sonore. Les informations concernant l'identité d'un son sont traitée le long de la voie ventrale di "Quoi". Cette voie est composée de regions situées dans le cortex temporal et frontal. L'objet de ce travail est d'étudier quels sont les neuro-mecanismes impliqués dans la représentation de nouveaux objets sonores appartenant à une meme catégorie sémantique ainsi que les phénomènes de plasticité à l'aide de l'imagerie électrique. Il a été montré que la discrimination de sons appartenant à différentes catégories sémantiques survient dans différentes aires situées le long la voie «Quoi» et suit une hiérarchie temporelle II a également été montré que la discrimination de sons appartenant à la même catégorie sémantique tels que les visages ou les voix, survient dans des aires spécifiques et représenteraient des stimuli particuliers. J'ai étudié comment les représentations corticales de sons appartenant à une même catégorie sémantique, dans ce cas des chants d'oiseaux, sont modifiées suite à un entraînement Pour ce faire, des sujets novices ont été entraînés à reconnaître des chants d'oiseaux spécifiques L'analyse des estimations des sources neuronales au cours du temps a montré que les representations des objets sonores activent de manière différente des régions situées le long de la vo,e ventrale en fonction du niveau d'expertise acquis grâce à l'entraînement. La reconnaissance des chants pour lesquels les sujets ont été entraînés implique un réseau sémantique principalement situé dans l'hémisphère gauche activé autour de 200ms. Au contraire, la reconnaissance des chants pour lesquels les sujets n'ont pas été entraînés survient plus tardivement dans des régions de plus bas niveau. J'ai ensuite étudié les mécanismes impliqués dans la reconnaissance et non reconnaissance de sons appartenant à une autre catégorie, .es battements de coeur. L'analyse des sources neuronales a montre que certaines régions du réseau sémantique lié à l'expertise acquise sont recrutées de maniere différente en fonction de la reconnaissance ou non reconnaissance du son La non reconnaissance des sons recrute des régions de plus bas niveau. La discrimination des bruits cardiaques est une tâche difficile et nécessite une écoute continue du son. J'ai étudié l'influence des réponses comportementales sur les effets de répétitions. L'analyse des sources neuronales a montré que la reconnaissance ou non reconnaissance des sons induisent des effets de repétition différents dans des régions situées en dehors des aires du réseau sémantique. Ainsi, les sons acquièrent un sens grâce à l'entraînement. Leur représentation corticale implique principalement un réseau d'aires cérébrales situé dans l'hémisphère gauche, dont l'activité est optimisée avec l'acquisition d'un certain niveau d'expertise, ainsi que d'autres régions qui ne sont pas liée au traitement de l'information sémantique. L'activité de ce réseau sémantique survient plus rapidemement que la prédiction par le modèle de la hiérarchie temporelle.

Validation of and comparison between a semidistributed rainfall-runoff hydrological model (PREVAH) and a spatially distributed snow-evolution model (SnowModel) for snow cover prediction in mountain ecosystems

Snow cover is an important control in mountain environments and a shift of the snow-free period triggered by climate warming can strongly impact ecosystem dynamics. Changing snow patterns can have severe effects on alpine plant distribution and diversity. It thus becomes urgent to provide spatially explicit assessments of snow cover changes that can be incorporated into correlative or empirical species distribution models (SDMs). Here, we provide for the first time a with a lower overestimation comparison of two physically based snow distribution models (PREVAH and SnowModel) to produce snow cover maps (SCMs) at a fine spatial resolution in a mountain landscape in Austria. SCMs have been evaluated with SPOT-HRVIR images and predictions of snow water equivalent from the two models with ground measurements. Finally, SCMs of the two models have been compared under a climate warming scenario for the end of the century. The predictive performances of PREVAH and SnowModel were similar when validated with the SPOT images. However, the tendency to overestimate snow cover was slightly lower with SnowModel during the accumulation period, whereas it was lower with PREVAH during the melting period. The rate of true positives during the melting period was two times higher on average with SnowModel with a lower overestimation of snow water equivalent. Our results allow for recommending the use of SnowModel in SDMs because it better captures persisting snow patches at the end of the snow season, which is important when modelling the response of species to long-lasting snow cover and evaluating whether they might survive under climate change.

Spinal cord injury affects the interplay between visual and sensorimotor representations of the body.

The brain integrates multiple sensory inputs, including somatosensory and visual inputs, to produce a representation of the body. Spinal cord injury (SCI) interrupts the communication between brain and body and the effects of this deafferentation on body representation are poorly understood. We investigated whether the relative weight of somatosensory and visual frames of reference for body representation is altered in individuals with incomplete or complete SCI (affecting lower limbs' somatosensation), with respect to controls. To study the influence of afferent somatosensory information on body representation, participants verbally judged the laterality of rotated images of feet, hands, and whole-bodies (mental rotation task) in two different postures (participants' body parts were hidden from view). We found that (i) complete SCI disrupts the influence of postural changes on the representation of the deafferented body parts (feet, but not hands) and (ii) regardless of posture, whole-body representation progressively deteriorates proportionally to SCI completeness. These results demonstrate that the cortical representation of the body is dynamic, responsive, and adaptable to contingent conditions, in that the role of somatosensation is altered and partially compensated with a change in the relative weight of somatosensory versus visual bodily representations.

Weakened functional connectivity in patients with psychogenic non-epileptic seizures (PNES) converges on basal ganglia.

BACKGROUND: Psychogenic non-epileptic seizures (PNES) are involuntary paroxysmal events that are unaccompanied by epileptiform EEG discharges. We hypothesised that PNES are a disorder of distributed brain networks resulting from their functional disconnection.The disconnection may underlie a dissociation mechanism that weakens the influence of unconsciously presented traumatising information but exerts maladaptive effects leading to episodic failures of behavioural control manifested by psychogenic 'seizures'. METHODS: To test this hypothesis, we compared functional connectivity (FC) derived from resting state high-density EEGs of 18 patients with PNES and 18 age-matched and gender-matched controls. To this end, the EEGs were transformed into source space using the local autoregressive average inverse solution. FC was estimated with a multivariate measure of lagged synchronisation in the θ, α and β frequency bands for 66 brain sites clustered into 18 regions. A multiple comparison permutation test was applied to deduce significant between-group differences in inter-regional and intraregional FC. RESULTS: The significant effect of PNES-a decrease in lagged FC between the basal ganglia and limbic, prefrontal, temporal, parietal and occipital regions-was found in the α band. CONCLUSION: We believe that this finding reveals a possible neurobiological substrate of PNES, which explains both attenuation of the effect of potentially disturbing mental representations and the occurrence of PNES episodes. By improving understanding of the aetiology of this condition, our results suggest a potential refinement of diagnostic criteria and management principles.