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Episode 8 15.03.2013
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Why can you smell a molecule you have never encountered before, and how does the nose use antagonism, binding proteins, and chemotopic maps to decode the chemical world? Tim Pearce explores the engineering principles behind biological olfaction.
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Tim Pearce provides a comprehensive tour of natural olfaction, from the molecular interactions at the receptor sheet to the computational principles that enable detection of thousands of diverse chemical compounds. He highlights the system’s remarkable foreignness property: unlike vision with its handful of receptor types, olfaction deploys over one percent of the genome to create a broad, relatively unbiased sampling of chemical space, capable of responding to novel molecules never previously encountered by the species.
The episode reveals several layers of molecular complexity that precede neural processing. Odorant binding proteins in the nasal mucosa act as selective transporters, shifting sorption spectra to capture hydrophobic compounds that would otherwise resist the liquid phase. Odor degrading enzymes terminate signals in a timely fashion. Most surprisingly, recent evidence shows that receptor-ligand interactions involve not just affinity but also efficacy, and that widespread antagonism between molecules means the neural response to mixtures is far from a linear sum of individual components. These nonlinear competitive interactions at the receptor level fundamentally shape the olfactory code.
Pearce describes a chemotopic organization of the receptor sheet where molecular features like carbon chain length, functional groups, and hydrophobicity map onto different spatial zones, driven partly by differential sorption along the airflow path and partly by the zonal expression of receptor families including ancient fish-derived class 1 receptors. Analysis of molecular descriptors reveals that despite hundreds of possible chemical features, the effective dimensionality of odor space is surprisingly low, with principal components capturing much of the perceptual variance.
The discussion also covers retronasal olfaction, where volatile compounds from food reach the receptor sheet through the back of the nose and produce qualitatively different percepts than the same compounds delivered orthonasally, even at the level of receptor sheet activation patterns. Pearce connects these biological insights to engineering principles for artificial olfactory systems, arguing that the conserved architectural motifs found across species from insects to mammals provide a blueprint for building chemical sensing systems.
Tagged as:
Binding Proteins chemical sensing Engineering Principles Interactions Receptor Receptor Sheet
About the author call_made
Both the triumphs of humanity and its most evil deeds have resulted from collaboration. In a time where humanity is required to aspire to the former and minimize the latter, the question arises of how collaboration arises and why it fails. Surprisingly, this phenomenon, so central to who we are, is not well understood. Hence, a collaborative effort is required to understand collaboration in its full biological, psychological, sociological, cultural, and economic complexity and to translate this understanding into operational impact. This series of podcasts is one step toward achieving these complementary goals. The Collaboration Podcast presents interviews with people who are central orchestrators of collaboration in various domains including business, government, science, art, health, sustainability, and the military. The discussions were conducted by Prof. Dr. Paul F.M.J. Verschure and members of the Program Advisory Committee of the Ernst Strungmann Forum on Collaboration (https://www.esforum.de/forums/ESF32_Collaboration.html) during 2021 and had the goal to sketch a map of opportunities, challenges, and obstacles in human collaboration. The forum took place in May 2022, and now we would like to share this series of interviews with a broader audience. The full report of the Forum will be published in 2023 by MIT Press. The podcast was produced by the Convergent Science Network (https://www.convergentsciencenetwork.org/). Context: The stability of social systems depends critically on realizing sustainable methods of “collaboration,” yet how and by which means collaboration is achieved is not clearly understood; neither are the conditions or processes that lead to its breakdown or failure. Collaboration can be understood as cooperation between agents toward mutually constructed goals. Part of the reason for our lack of understanding is that the phenomenon of collaboration is, by nature, a highly multidisciplinary problem, and effective research into its complexities has been difficult to achieve across the broad range of scientific and technical disciplines involved. The need for a fundamental understanding of collaboration, however, has become increasingly important. Not only does humankind demand answers as it attempts to address critical challenges at multiple scales (e.g., climate change, migration, enhanced automation, social and economic inequality), but ever-increasing technological and economic means of interconnecting people and societies are disrupting long-established, familiar patterns of how we interact. Radical technological changes that are ongoing have the potential to reshape collaboration in ways that are currently hard to predict or influence (e.g., by altering configurations in interaction, information creation, and modes of communication). On one hand, such changes could disrupt hitherto stable forms of collaboration by affecting critical communication channels and traditional roles, as can be observed in the rapidly changing patterns in governance, commerce, and social interaction. Conversely, technology could lead to the emergence of novel, successful forms of collaboration that deviate from traditional “hierarchical” architectures. Evidence of this can be seen in areas as diverse as highly automated manufacturing plants, the open science movement, collaborative software repositories, user-centered services, and the sharing of economy-based modes of organization. Without a fundamental understanding of the mechanisms, processes, and boundary conditions of collaboration, it is not possible to evaluate or predict which of these possible scenarios are sustainable or even plausible. The Forum “How Collaboration Arises and Why it Fails” (May 8–13, 2022, Location: Frankfurt am Main, Germany) Chairs: Andreas Roepstorff and Paul Verschure Program Advisory Committee: Jenna Bednar, Julia R. Lupp, Bhavani R. Rao , Andreas Roepstorff, Ferdinand von Siemens, and Paul Verschure
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