A Spiking Neural Network for Gas Discrimination using a Tin Oxide Sensor Array

International audienceWe propose a bio-inspired signal processing method for odor discrimination. A spiking neural network is trained with a supervised learning rule so as to classify the analog outputs from a monolithic 4×4 tin oxide gas sensor array implemented in our in-house 5 µm process. This scheme has been sucessfully tested on a discrimination task between 4 gases (hydrogen, ethanol, carbon monoxide, methane). Performance compares favorably to the one obtained with a common statistical classifier. Moreover, the simplicity of our method makes it well suited for building dedicated hardware for processing data from gas sensor arrays

A 4×4 Logarithmic Spike Timing Encoding Scheme for Olfactory Sensor Applications

International audienceThis paper presents a 4×4 logarithmic spike-timing encoding scheme used to translate the output of an integrated tin oxide gas sensor array into spike sequence, which is exploited to perform gas recognition. Hydrogen, Ethanol and Carbon monoxide were used to characterize the gas sensor array. The collected data were then used to test the proposed circuit for spike encoding and gas recognition. Simulation results illustrate that a particular analyte gas generates a unique spike pattern with certain spike ordering sequence, which is independent of the gas concentration. This unique spike sequence can thus be used to recognize different gases. In addition, the concentration information can also be extracted from the time-to-the-first spike in the sequence making it possible to perform not only gas/odor recognition but quantification as well

Influence of the synaptic inhibition on the information processing of olfactory bulb mitral cells

Le bulbe olfactif est principalement constitué de neurones excitateurs, dits cellules mitrales, interconnectés via des inter-neurones inhibiteurs, dits cellules granulaires. L'analyse de données expérimentales recueillies en condition in vitro dans des tranches de bulbe olfactif de rats révèle que le caractère phasé des potentiels d'action des cellules mitrales relativement aux oscillations du potentiel de champ local est largement atténué lorsque l'on bloque pharmacologiquement l'inhibition provenant des granules, mettant ainsi en évidence le rôle primordial de l'inhibition synaptique. Les fluctuations de la conductance synaptique inhibitrice sont corrélées à celles mesurées sur le potentiel de champ local. Une relation entre l'inhibition reçue et la phase des potentiels d'action est dévoilée. Un neurone aura plus de chance d'émettre en phase s'il reçoit un nombre important d'événements synaptiques inhibiteurs et si ces événements sont eux-même phasés. Ces résultats sont rassemblés au sein d'un modèle informatique de bulbe olfactif afin d'explorer les capacités de codage de l'interaction mitrale-granule. Après avoir montré que le transfert d'information des cellules mitrales semble plus résider dans leurs instants précis d'émission de potentiels d'action au cours des oscillations que dans leurs fréquences de décharges, une étude analytique conclut que la robustesse du code produit par les cellules mitrales lors des oscillations du réseau est conditionnée par une forte interaction synaptique. Nous appliquons notre modèle de bulbe olfactif pour reconnaître des odeurs à l'aide d'une matrice de capteurs de gaz artificiels.The olfactory bulb is mainly composed of excitatory cells, called mitral cells, interconnected via local inhibitory neurons, called granule cells. The analysis of electrophysiological data, recorded in vitro from rat olfactory bulb slices, shows that mitral cell firing is phase-locked to the fast local field potential oscillation. This phase-locking is largely reduced when the inhibitory synaptic conductance is pharmacologically blocked, hence highlighting the important role of synaptic inhibition. We find that the inhibitory conductance fluctuations are correlated to the local field potential oscillations. A relationship between the received inhibition and the phase of mitral action potentials is also revealed. The probability to fire a phase-locked action potential increases if the neuron receives a large number of inhibitory synaptic events, and if these events are themselves phase-locked. Results from the previous analysis are used to design a computational model of the olfactory bulb in order to explore the encoding capacity of the mitral-granule interplay. It appears likely that mitral cells encode information in precise spike timings rather than in firing rates. We therefore study analytically the influence of the number and the temporal dispersion of the received inhibitory synaptic events on the spike timing precision of mitral cells. Our study concludes that spike timing precision requires a strong synaptic coupling between mitral and granule cells. Lastly, our olfactory bulb model is applied to the recognition of odours by using an array of artificial gas sensors

Influence de l'inhibition synaptique sur le codage de l'information par les cellules mitrales du bulbe olfactif

This thesis studies the encoding of sensory information in olfactory bulb relay neurons by combining experimental data analysis with computer modelling. The olfactory bulb is mainly composed of excitatory cells, called mitral cells, interconnected via local inhibitory neurons, called granule cells.In the first part of the thesis, the analysis of electrophysiological data, recorded in vitro from rat olfactory bulb slices, shows that mitral cell firing is phase-locked to the fast local field potential oscillation. This phase-locking is largely reduced when the inhibitory synaptic conductance is pharmacologically blocked, hence highlighting the important role of synaptic inhibition. In order to extract the time course of the inhibitory synaptic conductance, we propose a new method based on the adjustment of a neuron model from experiments with local injections of a synaptic blocker. Using this method, we find that the inhibitory conductance fluctuations are correlated to the local field potential oscillations. A relationship between the received inhibition and the phase of mitral action potentials is also revealed. The probability to fire a phase-locked action potential increases if the neuron receives a large number of inhibitory synaptic events, and if these events are themselves phase-locked.In the second part of the thesis, results from the previous analysis are used to design a computational model of the olfactory bulb in order to explore the encoding capacity of the mitral-granule interplay. It appears likely that mitral cells encode information in precise spike timings rather than in firing rates. We therefore study analytically the influence of the number and the temporal dispersion of the received inhibitory synaptic events on the spike timing precision of mitral cells. Our study concludes that spike timing precision requires a strong synaptic coupling between mitral and granule cells. Lastly, our olfactory bulb model is applied to the recognition of odours by using an array of artificial gas sensors.Cette thèse étudie l'encodage de l'information sensorielle par les cellules relais du bulbe olfactif avec une approche associant analyse de données expérimentales et modélisation informatique. Le bulbe olfactif est principalement constitué de neurones excitateurs, dits cellules mitrales, interconnectés via des inter-neurones inhibiteurs, dits cellules granulaires.Dans un premier temps, l'analyse de données expérimentales recueillies en condition in vitro dans des tranches de bulbe olfactif de rats révèle le caractère phasé des potentiels d'action des cellules mitrales relativement aux oscillations du potentiel de champ local. Ce phasage est largement atténué lorsque l'on bloque pharmacologiquement l'inhibition provenant des granules, mettant ainsi en évidence le rôle primordial de l'inhibition synaptique. Afin d'extraire le décours temporel de la conductance synaptique inhibitrice, nous proposons une nouvelle méthode basée sur l'ajustement d'un modèle de neurone associé à l'injection de bloqueurs synaptiques. Grâce à celle-ci, nous observons que les fluctuations de la conductance synaptique inhibitrice sont corrélées à celles mesurées sur le potentiel de champ local. Une relation entre l'inhibition reçue et la phase des potentiels d'action est également dévoilée. Un neurone aura plus de chance d'émettre en phase s'il reçoit un nombre important d'événements synaptiques inhibiteurs et si ces événements sont eux-même phasés.Dans un deuxième temps, les résultats de cette analyse sont rassemblés au sein d'un modèle informatique de bulbe olfactif afin d'explorer les capacités de codage de l'interaction mitrale-granule. Après avoir montré que le transfert d'information des cellules mitrales semble plus résider dans leurs instants précis d'émission de potentiels d'action au cours des oscillations que dans leurs fréquences de décharges, nous étudions analytiquement l'influence du nombre d'événements synaptiques inhibiteurs reçus et de leur dispersion temporelle sur la précision de l'activité des cellules mitrales. Notre étude conclut que la robustesse du code produit par les cellules mitrales lors des oscillations du réseau est conditionnée par une forte interaction synaptique entre les cellules mitrales et les cellules granulaires. En dernier lieu, nous appliquons notre modèle de bulbe olfactif pour reconnaître des odeurs à l'aide d'une matrice de capteurs de gaz artificiels

Software Design for Low-Latency Visuo-Auditory Sensory Substitution on Mobile Devices

International audienceVisuo-auditory sensory substitution devices transform a video stream into an audio stream to help visually impaired people in situations where spatial information is required, such as avoiding moving obstacles. In these particular situations, the latency between an event in the real world and its auditory transduction is of paramount importance. In this article, we describe an optimized software architecture for low-latency video-to-audio transduction using current mobile hardware. We explain step-by-step the required computations and we report the corresponding measured latencies. The whole latency is approximately 65 ms with a capture resolution of 160 × 120 at 30 frames-per-second and 1000 sonified pixels per frame

Sunny Pointer: Designing a mouse pointer for people with peripheral vision loss

International audienceWe introduce here a new mouse cursor designed to facilitate the use of the mouse by people with peripheral vision loss. The pointer consists of a collection of converging straight lines covering the whole screen and following the position of the mouse cursor. We measured its positive effects in a group of participants with peripheral vision loss of different kinds and found that it can reduce by a factor of seven the time required to complete a targeting task using the mouse. Using eye tracking, we show that this system makes it possible to initiate the movement toward the target without having to precisely locate the mouse pointer. Using Fitts’ Law, we compare these performances with those of full visual field users in order to understand the relation between the accuracy of the estimated mouse cursor position and the index of performance obtained with our tool

Inhibitory control of spike timing precision

GABAergic inhibition via local interneurons may play a role in enhancing spike timing precision in principal cells, since it tends to eliminate the influence of initial conditions. However, both the number and the timing of inhibitory synaptic events may be variable across repeated trials. How does this variability affect the spike timing precision in principal neurons? In this paper, we derive an analytical expression for the spike output jitter as a function of the variability of the received inhibition. This study predicts that variable inhibition is especially tolerated as the number of inhibitory cells is large, which is consistent with experimental data from early olfactory systems (antennal lobe for insects, olfactory bulb for vertebrates).

Mobile video-to-audio transducer and motion detection for sensory substitution

International audienceVisuo-auditory sensory substitution systems are augmented reality devices that translate a video stream into an audio stream in order to help the blind in daily tasks requiring visuo-spatial information. In this work, we present both a new mobile device and a transcoding method specifically designed to sonify moving objects. Frame differencing is used to extract spatial features from the video stream and two-dimensional spatial information is converted into audio cues using pitch, interaural time difference, and interaural level difference. Using numerical methods, we attempt to reconstruct visuo-spatial information based on audio signals generated from various video stimuli. We show that despite a contrasted visual background and a highly lossy encoding method, the information in the audio signal is sufficient to allow object localization, object trajectory evaluation, object approach detection, and spatial separation of multiple objects. We also show that this type of audio signal can be interpreted by human users by asking 10 subjects to discriminate trajectories based on generated audio signals