Computational parallels between the biological olfactory pathway and its analogue 'the electronic nose': Part I. Biological olfaction.

Over the last fifteen years, we have witnessed a rapid expansion in the development of artificial odour sensing systems, or so called 'electronic nose' systems. Whilst the power of this approach to flavour analysis has undoubtedly been demonstrated by its recent application to various complex odours, it will be argued that the original research programme, aimed at developing a comparative model of the biological olfactory pathway, has degenerated into an attempt to obtain an ad hoc workable system, based around readily available sensor and pattern recognition (PARC) technologies. At the time, the first 'model' nose system reflected the limited understanding of sensory information processing carried out within the biological olfactory pathway. We are now presented with an opportunity to evaluate and re-assess the architecture for an electronic nose, in view of the recent advances in understanding the key processing principals exploited by the olfactory bulb and cortex in the identification and characterisation of molecular stimuli. In Part I of this paper, the rapid developments in the understanding of the information processing performed by the biological olfactory system are critically reviewed, and its relevance to current research in artificial olfaction is considered. Not only have the initial biochemical pathways involved in the transduction of odour stimuli been uncovered, but also computational models of the key synaptic circuits have advanced to the point where network simulations are clearly capable of odour discrimination. The key processing principles exploited in the olfactory pathway for overcoming operating constraints such as sensor drift/degeneration, limited sensitivity, and xenobiotic response are highlighted, so that their integration into the electronic analogue may be explored in Part II.