Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D47: Focus Session: Physics of Behavior III |
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Sponsoring Units: DBIO Room: 217B |
Monday, March 2, 2015 2:30PM - 3:06PM |
D47.00001: The neurobiology of individuality Invited Speaker: Benjamin de Bivort Individuals often display conspicuously different patterns of behavior, even when they are very closely related genetically. These differences give rise to our sense of individuality, but what is their molecular and neurobiological basis? Individuals that are nominally genetically identical differ at various molecular and neurobiological levels: cell-to-cell variation in somatic genomes, cell-to-cell variation in expression patterns, individual-to-individual variation in neuronal morphology and physiology, and individual-to-individual variation in patterns of brain activity. It is unknown which of these levels is fundamentally causal of behavioral differences. To investigate this problem, we use the fruit fly Drosophila melanogaster, whose genetic toolkit allows the manipulation of each of these mechanistic levels, and whose rapid lifecycle and small size allows for high-throughput automation of behavioral assays. This latter point is crucial; identifying inter-individual behavioral differences requires high sample sizes both within and across individual animals. Automated behavioral characterization is at the heart of our research strategy. In every behavior examined, individual flies have individual behavioral preferences, and we have begun to identify both neural genes and circuits that control the degree of behavioral variability between individuals. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D47.00002: Higher throughput high resolution multi-worm tracker Avelino Javer, Kezhi Li, Bertalan Gyenes, Andre Brown We have developed a high throughput imaging system for tracking multiple nematode worms at high resolution. The tracker consists of 6 cameras mounted on a motorized gantry so that up to 48 plates (each with approximately 30 worms) can be imaged without user intervention. To deal with the high data rate of the cameras we use real time processing to find worms and only save the immediately surrounding pixels. The system is also equipped with automatic oxygen and carbon dioxide control for observing stimulus response behaviour. We will describe the design and performance of the new system, some of the challenges of truly high throughput behaviour recording, and report preliminary results on inter-individual variation in behaviour as well as a quantitative analysis of \textit{C. elegans} response to hypoxia, oxygen reperfusion, and carbon dioxide. [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D47.00003: Locomotion and drag in wet and dry granular media Daniel Goldman, Robyn Kuckuk, Sarah Sharpe Many animals move within substrates such as soil and dry sand; the resistive properties of such granular materials (GM) can depend on water content and compaction, but little is known about how such parameters affect locomotion or the relevant physics of drag and penetration. We developed a system to create homogeneous wet GM of varying moisture content and compaction in quantities sufficient to study the burial and subsurface locomotion of the Ocellated skink (\emph{C. ocellatus}) a desert-generalist lizard. X-ray imaging revealed that in wet and dry GM the lizard slowly buried ($\approx 30$ seconds) propagating a wave from head to tail, while moving in a start-stop motion. During forward movement, the head oscillated, and the forelimb on the convex side of the body propelled the animal. Although body kinematics (and ``slip'') were similar in both substrates, the burial depth was smaller in wet GM. Penetration and drag force experiments on smooth cylinders revealed that wet GM was $\approx 3 \times$ more resistive than dry GM, suggesting that during burial the lizard operated near its maximum force producing capability and was thus constrained by environmental properties. [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D47.00004: Physics of Fission and Fusion for the Diagnostics and Monitoring of the Deadliest Illness of Mankind Arjun Saxena The physics of fission and fusion has been well known for the past several decades. It has been used primarily for destructive purposes (e. g., nuclear armaments) with both processes. However for peaceful purposes, e. g., generation of energy, only fission has been used, but not yet fusion. It is also well known that the deadliest illness of mankind is the group of illnesses called mental illnesses. A large segment of the world population is afflicted by them causing more loss of human lives, destruction of families, businesses and overall economy than all the other illnesses combined. Despite outstanding advancements in medical research and huge investments, unfortunately no diagnostic techniques have yet been found which can characterize the patient's mental illness. Consequently, no quantitative monitoring techniques are available to evaluate the efficacy of the various medicines used to treat the patients, and to develop them in the pharmaceutical labs. The purpose of this paper is to apply the constructive aspects of fission and fusion to identify the missing links in the diagnosis and treatment of mental illnesses. Each patient is a unique human being, not a disease or a group of symptoms. This makes it even more difficult to treat the patients suffering from mental illnes [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 3:54PM |
D47.00005: Sparse Coding of Natural Human Motion Yields Eigenmotions Consistent Across People Andreas Thomik, A. Aldo Faisal Providing a precise mathematical description of the structure of natural human movement is a challenging problem. We use a data-driven approach to seek a generative model of movement capturing the underlying simplicity of spatial and temporal structure of behaviour observed in daily life. In perception, the analysis of natural scenes has shown that sparse codes of such scenes are information theoretic efficient descriptors with direct neuronal correlates. Translating from perception to action, we identify a generative model of movement generation by the human motor system. Using wearable full-hand motion capture, we measure the digit movement of the human hand in daily life. We learn a dictionary of ``eigenmotions'' which we use for sparse encoding of the movement data. We show that the dictionaries are generally well preserved across subjects with small deviations accounting for individuality of the person and variability in tasks. Further, the dictionary elements represent motions which can naturally describe hand movements. Our findings suggest the motor system can compose complex movement behaviours out of the spatially and temporally sparse activation of ``eigenmotion'' neurons, and is consistent with data on grasp-type specificity of specialised neurons in the premotor cortex. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D47.00006: A stochastic model for bacterial dynamics toward point food sources with emergent run-and-tumble Hossein Jashnsaz, Tyler Nguyen, Horia Petrache, Steve Presse Despite stark differences in chemotactic signaling networks and flagellar physiology across bacterial species, all bacteria sense their environment through a series of stochastic detection events (``hits'') at their chemoreceptors and bias their random walk on the basis of this information. We present a general statistical model describing how bacteria locate point sources of food on the basis of stochastic event detection, rather than gradient information. We show how model parameters can be directly inferred using maximum likelihood methods from microscopy tracking data. We find that ``run-and-tumble'' dynamics naturally emerge from our statistical model and recapitulate known results from experiments when we consider bacterial dynamics in well-controlled chemoattractant gradients. However, our model goes beyond reproducing known run-and-tumble statistics. It also makes a number of predictions unique to bacteria tracking point sources. In our model, all parameters are directly inferred from tracking data thus there are no adjustable parameters; detection events by bacteria are assumed stochastic as they occur in nature; and our ``top-down'' modeling approach is broadly applicable across bacterial species. [Preview Abstract] |
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