Current cochlear implant systems use fast pulsatile stimulation to deliver the temporal modulations of speech and to, potentially, improve the neural representation of such modulations by restoring the independence of neural firing. The realization of these benefits may vary with other pulse rate-dependent temporal interactions that occur at the neural membrane, e.g., per(i)stimulatory adaptation and its post-stimulatory or forward masking effects. This study attempted to characterize adaptation and recovery of the electrically evoked compound action potential (ECAP) using probe pulses delivered within and following brief (100 ms) high-rate masker (1800 pps) pulse trains at various current levels in adults and children. With this stimulus paradigm, the ECAP amplitude typically achieved a steady state during the course of pulse train stimulation. The ECAP amplitude at steady state was, on average, a similar proportion (50-70%) of the amplitude at onset for various stimulus levels and in both age groups. However, long-term adaptation effects, evidenced by the decrease in onset ECAP amplitude, were greater in adults particularly at lower levels in the ECAP dynamic range. Instances of alternation in ECAP amplitude were seen at stimulus levels that were higher in the ECAP dynamic range. The forward masking effects of pulse train stimulation were quantified by the ECAP amplitude in response to a subsequent probe pulse normalized by the response to the same pulse presented alone. Pulse train forward masking increased with the level of the masker pulse train and decreased with the level of the probe stimulus. The recovery of the ECAP for probes that were lower in level than the masker pulse train was incomplete at 600 ms after masker offset, consistent with long-term cumulative effects observed in the response to the probe alone. Masker pulse trains that are lower in level than the probe pulse produced proportionally small decrements in the ECAP amplitude with complete recovery within 250 ms of pulse train offset particularly in adults. ECAP recovery of a probe preceded by a masker pulse train of equal level followed a monotonic or non-monotonic pattern consistent with a hypothesis of both adaptation and facilitation occurring with pulse train stimulation. The various patterns of recovery may attest to the occurrence of more than a single process in the same subset of nerve fibers or in different fibers. We hypothesize that the variations in the recovery patterns may be attributable to individual differences in the status of the auditory nerve and possibly, the variations in temporal interactions across the spatial domain at different stimulus levels. Finally, the probe-evoked ECAP amplitude at steady state in children and briefly, e.g., 20 ms, after pulse train offset in both age groups could be predicted by the ECAP amplitude in response to the same probe pulse when preceded at a brief interval (1.2 or 2 ms) by a single masker pulse of the same level as the masker pulse train. Further investigation may reveal if the observed differences in neural responsiveness to pulsatile stimulation, among individuals account for differences in psychophysical measures, including speech perception and whether there may be an "optimal" neural output that could be evoked by an individually "optimized" signal.

Dans l'Arctique, le risque de transmission de maladies zoonotiques comme la rage est encore une préoccupation pour la santé publique, avec plusieurs cas rapportés chaque année chez différentes espèces animales. L’interface entre la faune sauvage, les animaux domestiques et les humains pour la transmission de maladies sera en augmentation en raison des pressions grandissantes du développement anthropique et du réchauffement climatique. Les interactions directes entre les chiens domestiques des villages nordiques et les renards sauvages, les principales sources d’exposition à la rage, sont des évènements critiques pour l’exposition des humains au virus, mais très peu d’études se sont attardées à ce sujet. Les objectifs de ce projet sont 1- de décrire et de quantifier l’activité spatiale et temporelle des renards et des chiens libres et d’identifier les facteurs anthropiques et environnementaux qui influencent leur présence à proximité et dans les villages nordiques, 2- de quantifier les contacts directs et le potentiel d’interactions entre les renards et les chiens libres afin de mieux identifier les périodes et les zones avec un risque de transmission de la rage, 3- de comparer et discuter des résultats de l’activité des renards et des chiens libres et leur potentiel d’interactions entre les deux villages nordiques à l’étude et 4- d’identifier des méthodes de gestion pour diminuer les opportunités d’interactions entre les renards et les chiens libres. Afin de détecter la présence des deux carnivores, un réseau de caméras automatiques a été installé sur une grille spatiale autour et à l’intérieur de deux villages typiques du Nord, Kuujjuaq (près de la limite des arbres) et Inukjuak (à > 100 km de la limite des arbres). Pour chaque station caméra, différents facteurs anthropiques et environnementaux ont été évalués (distance au dépotoir, distance à l’aéroport, densité d’habitations, densité de chiens de traîneau, distance aux rues, distance à l’eau, indice de végétation). Les contacts directs et les indices d’interaction ont été calculés pour évaluer le potentiel d’interactions entre les renards et les chiens libres. Les opportunités d’interactions entre les renards et les chiens sont plus élevées à l’aube et au crépuscule pendant les mois d'octobre et de novembre en périphérie des deux villages, particulièrement près des chiens de traîneau et légèrement près du dépotoir municipal (KU) et de l’aéroport (IN). Les renards roux et les renards arctiques ont été observés à proximité et dans les deux villages, mais les renards roux sont plus souvent observés à Kuujjuaq (87% des observations) qu’à Inukjuak (renards arctiques : 74% des observations), ce qui reflète également des particularités biotiques et abiotiques uniques à chaque village. Les résultats suggèrent que les opportunités d’interactions entre les renards et les chiens représentent un risque d’exposition à la rage pour les chiens et les humains, et possiblement pour d’autres pathogènes nordiques transmissibles entre les chiens et la faune. Cependant, les évènements de contacts directs interspécifiques renard-chien sont rares et les opportunités d’interactions sont concentrées dans le temps et dans des zones restreintes, ce qui peut aider à cibler des mesures préventives visant à limiter les évènements de transmission. Cette étude fournit la première documentation sur l'activité des renards et leurs interactions avec les chiens libres dans les villages de l'Arctique. L’application d’une approche « Une seule Santé » devrait être utilisée pour prévenir ou diminuer le risque de transmission de la rage entre les renards et les chiens. / In the Arctic, the risk of transmission of zoonotic diseases like rabies is still a public health concern, with several cases reported each year in different animal species. The interface between wildlife, domestic animals and humans for disease transmission will be increasing due to pressures from anthropogenic development and global warming. Direct interactions between domestic dogs in northern communities and wild foxes, the main source of rabies exposure, are critical of human exposure to the virus, but very few studies have focused on this. The objectives of this project are 1- to describe and quantify the spatial and temporal activity of free-ranging dogs and foxes, and identify the anthropogenic and environmental factors that influence their presence near and within northern villages, 2- to quantify direct contacts and the potential for interactions between free-ranging dogs and foxes in order to better identify periods and areas of higher risk of rabies transmission, 3- to compare and contrast dog-fox activity and interactions between the two northern villages under study, and 4- to identify management methods to reduce opportunities for fox-dog interactions. To detect the presence of the two carnivores, we set up a network of automatic cameras near and within two typical northern villages, i.e., Kuujjuaq (near the tree line) and Inukjuak (> 100 km from the tree line). For each camera, different anthropogenic and environmental factors were evaluated (distance to the landfill, distance to the airport, density of dwellings, density of sled dogs, distance to streets, distance to water, vegetation index). Direct contacts and interaction index were calculated to assess the potential for interactions between foxes and free-roaming dogs. Interaction opportunities between foxes and dogs are more likely to occur at dawn and dusk during the months of October and November, and on the outskirts of both villages, particularly near sled dogs and slightly nearer to the landfill (KU) and the airport (IN). Red and Arctic foxes were observed in and around both villages, but red foxes were more frequently observed in Kuujjuaq (87% of observations) while Arctic foxes were more frequent in Inukjuak (74% of observations), which also reflects the biotic and abiotic particularities specific to each village. These results suggest that fox-dog contacts around and within the village are likely, posing a real risk of peri-domestic rabies transmission to dogs and humans, and possibly for other northern pathogens transmissible between wildlife and dogs. Nevertheless, interspecific direct contact events are rare and interaction opportunities are concentrated in time and space, which may help target preventive measures aimed at limiting transmission events. This study provides the first documentation on the activity of foxes and their interactions with dogs and humans in Arctic communities. Considering the potential risk-by-proximity described in our study, a “One Health” approach could be applied to prevent or lower fox-dog rabies transmission.