Gilles Sicard

Receptor cell responses to odorants: Similarities and differences among odorants

An extensive exploration of the discriminating properties of olfactory receptors cells has been conducted in our laboratory through the statistical processing of single cell responses recorded in the frogs olfactory epithelium. Similarities between odorant stimulating properties could be demonstrated by comparing the complex response profiles of receptor cells, resulting in the concept of odorant groups which depicts consistent relationships found between some odorous compounds. The recording technique limits the number of odorants which can be tested and compared within the same series of experiments. Thus, based upon previous studies we have chosen a specific set of 20 odorants whose characteristics are known but, up to this time, have not been compared in the same experimental system. These odorants were: acetophenone, anisole, n-butanol, DL-camphor, cyclodecanone, 1,8-cineole, p-cymene, D-citronellol, n-heptanol, isoamyl acetate, isovaleric acid, D-limonene, methyl amylketone, L-menthol, phenol, thiophenol, pyridine, thymol, cyclohexanol, cyclohexanone. The pattern of similarities between these odorants, as delineated with the aid of correlation coefficient computation, factor analysis and non-hierarchical taxonomy, confirms the reality of several odorant groups previously suggested and describes their cross-relationships. The receptor mechanisms underlying these odorant groups are discussed. Because reliable prominent features of the olfactory stimulus space can be established on an objective basis, the findings are proposed as a reference for future studies on other aspects of olfactory discrimination.

Functional Anatomy of Perceptual and Semantic Processing for Odors

The functional anatomy of perceptual and semantic processings for odors was studied using positron emission tomography (PET). The first experiment was a pretest in which 71 normal subjects were asked to rate 185 odorants in terms of intensity, familiarity, hedonicity, and comestibility and to name the odorants. This pretest was necessary to select the most appropriate stimuli for the different cognitive tasks of the second experiment. The second one was a PET experiment in which 15 normal subjects were scanned using the water bolus method to measure regional cerebral blood flow (rCBF) during the performance in three conditions. In the first (perceptual) condition, subjects were asked to judge whether an odor was familiar or not. In the second (semantic) condition, subjects had to decide whether an odor corresponded to a comestible item or not. In the third (detection) condition, subjects had to judge whether the perceived stimulus was made of an odor or was just air. It was hypothetized that the three tasks were hierarchically organized from a superficial detection level to a deep semantic level. Odorants were presented with an air-flow olfactometer, which allowed the stimulations to be synchronized with breathing. Subtraction of activation images obtained between familiarity and control judgments revealed that familiarity judgments were mainly associated with the activity of the right orbito-frontal area, the subcallosal gyrus, the left inferior frontal gyrus, the left superior frontal gyrus, and the anterior cingulate (Brodmanns areas 11, 25, 47, 9, and 32, respectively). The comestibility minus familiarity comparison showed that comestibility judgments selectively activated the primary visual areas. In contrast, a decrease in rCBF was observed in these same visual areas for familiarity judgments and in the orbitofrontal area for comestibility judgments. These results suggest that orbito-frontal and visual regions interact in odor processing in a complementary way, depending on the task requirements.

A new class of asynchronous A/D converters based on time quantization

This work is a contribution to a drastic change in standard signal processing chains. The main objective is to reduce the power consumption by one or two orders of magnitude. Integrated Smart Devices and Communicating Objects are application domains targeted by this work. In this context, we present a new class of Analog-to-Digital Converters (ADCs), based on an irregular sampling of the analog signal, and an asynchronous design. Because they are not conventional, a complete design methodology is presented. It determines their characteristics given the required effective number of bits and the analog signal properties. it is shown that our approach leads to a significant reduction in terms of hardware complexity and power consumption. A prototype has been designed for speech applications, using the STMicroelectronics 0.18-/spl mu/m CMOS technology. Electrical simulations prove that the factor of merit is increased by more than one order of magnitude compared to synchronous Nyquist ADCs.

Olfactory discrimination over a wide concentration range. Comparison of receptor cell and bulb neuron abilities

Until now, olfactory discrimination had never been investigated using stimuli delivered over a wide concentration range. However, the fact that intensity variations might influence qualitative discrimination has been suggested in numerous physiological and psychophysical studies. The aim of the present work was to investigate qualitative coding mechanisms when stimulus intensity varies. For this purpose, receptor cell and olfactory bulb neuron unit activities were recorded in response to 2-s pulse delivery of 4 odorants available at 20 discrete concentration values over a range from 1 x 10(-6) to 5.62 x 10(-2) of saturation. Two types of mathematical analyses, Pearsons r correlation coefficient calculation and principal component factor analysis, were applied to odor-evoked discharge frequencies. In both receptor cells and bulb neurons, qualitative discrimination abilities were found to increase with stimulus concentration. Furthermore, the results suggest that the olfactory bulb can send a discriminant and specific message at lower concentrations than the olfactory mucosa. The amplifying role of convergence of primary afferences onto olfactory glomeruli could account for this ability of the bulb neurons.

Static Implementation of QDI Asynchronous Primitives

To fairly compare the performance of an asynchronous ASIC to its homologous synchronous one requires the availability of a dedicated asynchronous library. In this paper we present TAL_130nm a standard cell library dedicated to the design of QDI asynchronous circuits. Cell selection and sizing rules applied to develop TAL_130nm are detailed. It is shown that significant area and power savings as well as speed improvements can be obtained.

Olfactory discrimination of structurally related molecules: receptor cell responses to camphoraceous odorants.

Electrophysiological investigations of the selective sensitivity of receptor cells have shown that odorants could be distributed into groups according to the profiles of responses that they elicited from a population of receptor cells. As the concept of odorant group plays an important role in the understanding of olfactory coding, an attempt was made to investigate in detail the group properties of a number of structurally and qualitatively related molecules: 1,8 cineole, DL-camphor, borneol, iso-borneol, adamantane, fenchone, fenchyl alcohol, 3,3,5-tri-methyl cyclohexanone, camphene, 1,1,2,2-tetra-bromoethane. These odorants, along with several other representatives of other odorant groups, were utilized to stimulate a set of 71 individually recorded receptor cells. Factor analysis of electrophysiological data demonstrated that the grouping of odorants with camphor could be predicted on the basis of the shape and size of the molecules. The analysis also showed that even a clearly defined odorant group such as the camphor group is not likely to be determined by a single type of receptor site.

An on-pixel FPN reduction method for a high dynamic range CMO S imager

A high dynamic range CMOS image sensor implementing a fixed pattern noise (FPN) reduction method is presented. The high dynamic range is reach through a logarithmic architecture pixel. An on-chip calibration method is implemented to reduce the FPN caused by process variations, weakness of this architecture. The basic principle is the calibration of each pixel against an in-pixel reference current in place of the diode photocurrent. Two pixel levels corresponding to the photocurrent and a known reference current become available for every pixel Then a double sampling technique allows removing offsets due to threshold voltage variations. An innovation of this work consists in the implementation of the current calibration source totally inside the pixel, allowing a better precision of the FPN compensation and lower power consumption. This FPN reduction method is performed while keeping only four transistors per pixel. A 128times128 pixels test chip has been designed and fabricated in 0.35 mum, 3.3 V CMOS standard technology. Pixel measures 10times10.6 mum2 with a fill factor of 33%. The dynamic range is up to 100dB with a frame rate up to 30 images per second and a measured FPN of 2.9% rms of the total dynamic range.

A 45nm CMOS 0.35v-optimized standard cell library for ultra-low power applications

Ultra-low voltage is now a well known solution for energy constrained applications designed using nanometric process technologies. This work is focused on setting-up an automated methodology to enable the design of ultra-low voltage digital circuits exclusively using standard EDA tools. To achieve this goal, a 0.35V energy-delay optimized library was developed. This library, fully compliant with standard library design flow and characterization, was verified through the design and fabrication of a BCH decoder circuit, following a standard front-end to back-end flow. It performs at 457 kHz, with a total energy consumption of 2.9fJ per cycle.

The Lyon Clinical Olfactory Test: Validation and Measurement of Hyposmia and Anosmia in Healthy and Diseased Populations

The LCOT is a self-administered test designed to assess olfactory deficits. Altogether, 525 subjects contributed to the validation. Elderly participants were well represented in this sample. In a validation study (study 1), 407 healthy and 17 anosmic volunteers between 15 and 91 years of age underwent threshold, supraliminal detection, and identification testing. Cutoff values for normosmia and hyposmia were calculated and applied in a second study in a group of patients with smell complaints and in a group of Alzheimer patients with age-matched controls. Incidence of smell deficit was estimated at 5.6% in the healthy population of study 1, and at 16% in the elderly control group of study 2. Assessment of the ability of each subtest to discriminate between groups showed that LCOT is relevant to differentiating between perception and identification deficits and between Alzheimers and hyposmic patients.

Low-Power Asynchronous A/D Conversion

This paper presents a new architecture of Analog-to-Digital Converter (ADC) for low-power applications. The converter is a tracking circuit without any global clock, based on an asynchronous design. Samples conversion is only triggered by the analog input signal amplitude variations, hence an irregular sampling of it. System simulations demonstrate that a significative reduction of the circuit activity can be achieved with it. Moreover, such a converter has been designed with 6-bit resolution, using a 0.18-µm, 1.8-V standard CMOS technology from ST-Microelectronics. Electrical simulations show that, the asynchronous converter has an average power dissipation of only 1.9mW in the worst case, with a sample conversion time of 37.9ns, and an important noise reduction is achieved, compared to its synchronous counterparts.