Equation-oriented specification of neural models for simulations

Simulating biological neuronal networks is a core method of research in computational neuroscience. A full specification of such a network model includes a description of the dynamics and state changes of neurons and synapses, as well as the synaptic connectivity patterns and the initial values of all parameters. A standard approach in neuronal modeling software is to build network models based on a library of pre-defined components and mechanisms; if a model component does not yet exist, it has to be defined in a special-purpose or general low-level language and potentially be compiled and linked with the simulator. Here we propose an alternative approach that allows flexible definition of models by writing textual descriptions based on mathematical notation. We demonstrate that this approach allows the definition of a wide range of models with minimal syntax. Furthermore, such explicit model descriptions allow the generation of executable code for various target languages and devices, since the description is not tied to an implementation. Finally, this approach also has advantages for readability and reproducibility, because the model description is fully explicit, and because it can be automatically parsed and transformed into formatted descriptions. The presented approach has been implemented in the Brian2 simulator

Estimation of the low-frequency components of the head-related transfer functions of animals from photographs

Reliable animal head-related transfer function (HRTF) estimation procedures are needed for several practical applications. For example, to investigate the neuronal mechanisms of sound localization using virtual acoustic spaces, or to have a quantitative description of the di erent localization cues available to a given animal species. Here two established techniques are combined to estimate an animal's HRTF from photographs by taking into account as much morphological detail as possible. The rst step of the method consists in building a 3D-model of the animal from pictures taken with a standard camera. The HRTFs are then estimated by means of a rapid boundary-element-method implementation. This combined method is validated on a taxidermist model of a cat by comparing binaural and monaural localization cues extracted from estimated and measured HRTFs. It is shown that it provides a reliable way to estimate low-frequency HRTF, which are di cult to obtain with standard acoustical measurements procedures because of re ections.ERC StG 24013

On the variation of interaural time differences with frequency

Interaural time difference (ITD) is a major cue to sound localization in humans and animals. For a given subject and position in space, ITD depends on frequency. This variation is analyzed here using a head related transfer functions (HRTFs) database collected from the literature and comprising human HRTFs from 130 subjects and animal HRTFs from six specimens of different species. For humans, the ITD is found to vary with frequency in a way that shows consistent differences with respect to a spherical head model. Maximal ITD values were found to be about 800 ls in low frequencies and 600 ls in high frequencies. The ITD variation with frequency (up to 200 ls for some positions) occurs within the frequency range where ITD is used to judge the lateral position of a sound source. In addition, ITD varies substantially within the bandwidth of a single auditory filter, leading to systematic differences between envelope and fine-structure ITDs. Because the frequency-dependent pattern of ITD does not display spherical symmetries, it potentially provides cues to elevation and resolves front/back confusion. The fact that the relation between position and ITDs strongly depends on the sound’s spectrum in turn suggests that humans and animals make use of this relationship for the localization of sounds

Indices temporels pour la localisation des sources sonores en azimuth

Azimuth sound localization in many animals relies on the processing of differences in time-of-arrival of the low-frequency sounds at both ears: the interaural time differences (ITD). It was observed in some species that this cue depends on the spectrum of the signal emitted by the source. Yet, this variation is often discarded, as humans and animals are assumed to be insensitive to it. The purpose of this thesis is to assess this dependency using acoustical techniques, and explore the consequences of this additional complexity on the neurophysiology and psychophysics of sound localization. In the vicinity of rigid spheres, a sound field is diffracted, leading to frequency-dependent wave propagation regimes. Therefore, when the head is modeled as a rigid sphere, the ITD for a given position is a frequency-dependent quantity. I show that this is indeed reflected on human ITDs by studying acoustical recordings for a large number of human and animal subjects. Furthermore, I explain the effect of this variation at two scales. Locally in frequency the ITD introduces different envelope and fine structure delays in the signals reaching the ears. Second the ITD for low-frequency sounds is generally bigger than for high frequency sounds coming from the same position. In a second part, I introduce and discuss the current views on the binaural ITD-sensitive system in mammals. I expose that the heterogenous responses of such cells are well predicted when it is assumed that they are tuned to frequency-dependent ITDs. Furthermore, I discuss how those cells can be made to be tuned to a particular position in space irregardless of the frequency content of the stimulus. Overall, I argue that current data in mammals is consistent with the hypothesis that cells are tuned to a single position in space. Finally, I explore the impact of the frequency-dependence of ITD on human behavior, using psychoacoustical techniques. Subjects are asked to match the lateral position of sounds presented with different frequency content. Those results suggest that humans perceive sounds with different frequency contents at the same position provided that they have different ITDs, as predicted from acoustical data. The extent to which this occurs is well predicted by a spherical model of the head. Combining approaches from different fields, I show that the binaural system is remarkably adapted to the cues available in its environment. This processing strategy used by animals can be of great inspiration to the design of robotic systems.La localisation des sources en azimuth repose sur le traitement des différences de temps d'arrivée des sons à chacune des oreilles: les différences interaurales de temps (``Interaural Time Differences'' (ITD)). Pour certaines espèces, il a été montré que cet indice dépendait du spectre du signal émis par la source. Pourtant, cette variation est souvent ignorée, les humains et les animaux étant supposés ne pas y être sensibles. Le but de cette thèse est d'étudier cette dépendance en utilisant des méthodes acoustiques, puis d'en explorer les conséquences tant au niveau électrophysiologique qu'au niveau de la psychophysique humaine. A la proximité de sphères rigides, le champ sonore est diffracté, ce qui donne lieu à des régimes de propagation de l'onde sonore différents selon la fréquence. En conséquence, quand la tête d'un animal est modélisée par une sphère rigide, l'ITD pour une position donnée dépend de la fréquence. Je montre que cet effet est reflété dans les indices humains en analysant des enregistrements acoustiques pour de nombreux sujets. De plus, j'explique cet effet à deux échelles: localement en fréquence, la variation de l'ITD donne lieu à différents délais interauraux dans l'enveloppe et la structure fine des signaux qui atteignent les oreilles. Deuxièmement, l'ITD de sons basses-fréquences est généralement plus grand que celui pour des sons hautes-fréquences venant de la même position. Dans une seconde partie, je discute l'état de l'art sur le système binaural sensible à l'ITD chez les mammifères. J'expose que l'hétérogénéité des réponses de ces neurones est prédite lorsque l'on fait l'hypothèse que les cellules encodent des ITDs variables avec la fréquence. De plus, je discute comment ces cellules peuvent être sensibles à une position dans l'espace, quel que soit le spectre du signal émis par la source. De manière générale, j'argumente que les données disponibles chez les mammifères sont en adéquation avec l'hypothèse de cellules sélectives à une position dans l'espace. Enfin, j'explore l'impact de la dépendance en fréquence de l'ITD sur le comportement humain, en utilisant des techniques psychoacoustiques. Les sujets doivent faire correspondre la position latérale de deux sons qui n'ont pas le même spectre. Les résultats suggèrent que les humains perçoivent des sons avec différents spectres à la même position lorsqu'ils ont des ITDs différents, comme prédit part des enregistrements acoustiques. De plus, cet effet est prédit par un modèle sphérique de la tête du sujet. En combinant des approches de différents domaines, je montre que le système binaural est remarquablement adapté aux indices disponibles dans son environnement. Cette stratégie de localisation des sources utilisée par les animaux peut être d'une grande inspiration dans le développement de systèmes robotiques

Emergence of ITD tuning in the MSO with a realistic periphery model

International audienceTo localize sounds in the environment, animals mostly rely on spectro-temporal cues originating from the physical disparities of the sound waveforms impacting the two ears. Among those, the Interaural Time Difference (ITD) has been shown to be crucial in mammals for locating low-frequency sounds, and is known to be processed by neurons in a particular structure, the Medial Superior Olive (MSO). While it is classically considered that the emergence of ITD selectivity in a neuron of the MSO is simply due to differences in the axonal delays originating from the two ears and impinging those neu-rons (the so called " delay-line " model [1]), experimental evidence shows that the best delay (the ITD at which the neuron's firing rate is maximum) is also dependent on the frequency of the sound [2]. To investigate more on this challenging experimental observation, we developed a realistic periphery model to mimic cochlear inputs from auditory nerves fibers onto the MSO. Using known plasticity rules such as Spike Timing Dependent Plasticity to structure the wiring from those connections onto the MSO, we extend the work that has already been performed [3], and study the emergence of binaural tuning in the MSO in a realistic scenario. The system is trained with binaural sounds such as white noise, and then, as in most experimental papers, we tested the ITD selectivity of cells in the MSO by presenting pure tones at various frequencies. Finally, we discuss, from a coding point of view the potential implications raised by the frequency dependence of the best delay. As pointed out by recent work [4], with such a frequency-dependent best delay, neu-rons in the MSO should be seen as coding for a particular position in space, rather than for just a fixed delay difference

Use of Cement-Augmented Percutaneous Pedicular Screws in the Management of Multifocal Tumoral Spinal Fractures

Study Design Retrospective case series observational study. Purpose Cancer patients are often aged and are further weakened by their illness and treatments. Our goal was to evaluate the efficiency and safety of using minimally invasive techniques to operate on spinal fractures in these patients. Overview of Literature Vertebroplasty is now considered to be a safe technique that allows a significant reduction of the pain induced by a spinal tumoral fracture. However, few papers describe the kyphosis reduction that can be achieved by combining percutaneous fixation and anterior vertebral reconstruction. Methods We studied 35 patients seen between December 2013 and October 2016 who had at least one pathological spinal fracture and multiple vertebral metastases. The population’s mean age was 67 years, and no patients included had preoperative neurological deficits. The patients underwent a minimally invasive surgery consisting of a percutaneous pedicular fixation with cement-enhanced screws and anterior reconstruction comprising kyphoplasty when possible or corpectomy in cases of excessive damage to the vertebral body. Back pain, traumatic local and regional kyphosis, and Beck’s Index were collected pre- and postoperatively, and at 3-, 6-, and 12-month follow-ups. Results Mean follow-up time was 13.4 months. Significant reductions in back pain (p<0.001) and local (p<0.001) and regional kyphosis (p=0.006) were found at the 6-month follow-up (alpha risk level <0.05). Beck’s Index was also significantly increased, indicating good restoration of the anterior vertebral height. By the final follow-up, no screws had fallen/pulled out. There were no infectious or neurological complications. Conclusions Percutaneous cement-enhanced fixation for pathological fractures has proven a safe and efficient technique in our experience, enabling weak patients to rapidly become ambulatory again without complications. Further follow-up of the patients is necessary to assess the long-term effects of this technique and the continued quality of life of our patients

Neural tuning matches frequency-dependent time differences between the ears

The time it takes a sound to travel from source to ear differs between the ears and creates an interaural delay. It varies systematically with spatial direction and is generally modeled as a pure time delay, independent of frequency. In acoustical recordings, we found that interaural delay varies with frequency at a fine scale. In physiological recordings of midbrain neurons sensitive to interaural delay, we found that preferred delay also varies with sound frequency. Similar observations reported earlier were not incorporated in a functional framework. We find that the frequency dependence of acoustical and physiological interaural delays are matched in key respects. This suggests that binaural neurons are tuned to acoustical features of ecological environments, rather than to fixed interaural delays. Using recordings from the nerve and brainstem we show that this tuning may emerge from neurons detecting coincidences between input fibers that are mistuned in frequency.status: publishe