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Gain control in insect olfaction for efficient odor recognition Ramón Huerta Institute for Nonlinear Science UCSD
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What is time and dynamics buying us for pattern recognition purposes? One way to tackle it 1. Start from the basics of pattern recognition: organization, connectivity, etc.. 2. See when dynamics (time) is required. The goal
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How does an engineer address a pattern recognition problem? 1.Feature extraction. For example: edges, shapes, textures, etc… 2.Machine learning. For example: ANN, RBF, SVM, Fisher, etc.. What is easy ? What is difficult? 1.Feature extraction: very difficult (cooking phase) 2.Machine learning: very easy (automatic phase)
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Feature Extraction High divergence-convergence ratios from layer to layer. Antennal Lobe (AL) Mushroom body (MB) Antenna Mushroom body lobes Location of learning How insects appear to do it Machine Learning Stage
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Bad news The feature extraction stage is mostly genetically prewired Good news The machine learning section seems to be “plastic”
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Feature Extraction Antennal Lobe (AL) Mushroom body (MB) Antenna Mushroom body lobes Machine Learning Stage Spatio-temporal coding occurs hereNo evidence of time here
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The basic question Can we implement a learning machine with fan-in, fan-out connectivities, the proportion of neurons, local synaptic plasticity, and inhibition? Huerta et al, Neural Computation 16(8) 1601-1640 (2004)
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Marr, D. (1969). A theory of cerebellar cortex. J. Physiol., 202:437- 470. Marr, D. (1970). A theory for cerebral neocortex. Proceedings of the Royal Society of London B, 176:161-234. Marr, D. (1971). Simple memory: a theory for archicortex. Phil. Trans. Royal Soc. London, 262:23-81. Willshaw D, Buneman O P, & Longuet-Higgins, HC (1969) Non-holographic associative memory, Nature 222:960
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CALYX Display Layer Intrinsic Kenyon Cells PNs (~800)iKC(~50000)eKC(100?) AL MB lobes Decision layer Extrinsic Kenyon Cells No learning required Learning required k-winner- take-all Stage I: Transformation into a large display Stage II: Learning “perception” of odors
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KCs coordinates 1 0 0 0 1 0 1 1 Class 1Class 2 1 0 1 AL coordinates Hyperplane: Connections from the KCs to MB lobes MB lobe neuron: decision
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Odor classification Odor 4 Odor 3 Odor 2 Odor 1 Odor N Class 1 Class 2
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Sparse code Probability of discrimination # of active KCs
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Capacity for discriminating We look for maximum number of odors that can be discriminated for different activate KCs, Note: we use Drosophila numbers # of active KCs TOTAL # OF ODORS
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It has been shown both in Locust (Laurent) and Honeybee (Menzel) the existence of sparse code ~1% activity
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Narrow areas of sparse activity Without GAIN CONTROL There can be major FAILURE
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Feature Extraction Antennal Lobe (AL) Mushroom body (MB) Antenna Mushroom body lobes Machine Learning Stage GAIN CONTROL But nobody knows why
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Evidence for gain control in the AL These neurons can fire up to100 Hz The baseline firing rate is 3-4Hz Data from Mark Stopfer, Vivek Jayaraman and Gilles Laurent
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Honeybee: Galizia’s group There seems to be local GABA circuits in the MBs. Locust and honeybee circuits are different: Honeybee 10 times more inhibitory neurons than locust
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Let’s concentrate on the locust problem: How do we design the AL circuit such that it has gain control?
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Mean field of 4 populations of neurons
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We apply mean field
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Define new set of variables To obtain the mean field eq. Where we use
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We look for the condition such that Whose condition is: with and This works if and are linear BUT! The gain control depends only on the inhibitory connections
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The excitatory neurons are not at high spiking frequencies or silent, but but not very high (3-4) Hz. So SIMULATIONS: 400 Neurons
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The gain control condition from the MF can be estimated as
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A few conclusions: Gain control can be implemented in the AL network It can be controlled by the inhibitory connectivity. The rest of the parameters are free. Things to do: I do not know whether under different odor intensities the AL representation is the same.
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Thanks to Marta Garcia-Sanchez Loig Vaugier Thomas Nowotny Misha Rabinovich Vivek Jayaraman Ofer Mazor Gilles Laurent
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