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A Typical Visual Physiology Setup

The Physiologist’s FriendChip A product of the Institute of Neuroinformatics “The only FriendChip you’ll ever need”. Stimulus. A Typical Visual Physiology Setup. Several communicating machines, custom software. Months of development and debugging…. Goal.

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A Typical Visual Physiology Setup

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  1. The Physiologist’s FriendChipA product of the Institute of Neuroinformatics“The only FriendChip you’ll ever need”

  2. Stimulus A Typical Visual Physiology Setup Several communicating machines, custom software. Months of development and debugging…

  3. Goal • To make a practical chip that acts as a substitute animal for experiment design or demonstration. • It should provide spiking neurons from retina and early visual cortex. • It should be plug and play: • battery power • no computer • no knobs.

  4. Volume control Chip + Lens Onboard speaker Output selector External speaker jack BNC connector

  5. 1 Average 2 5 7 Simple cells 4 3 8 On Off 6 Excitatory Inhibitory Chip schematic Photodiodes Photoreceptors Horizontal/Bipolar Ganglion Synapses Brighter than average Darker than average Bias generator

  6. Layout Photodiodes Biases Photoreceptors Bipolar/Horizontal cells Ganglion & Simple cells Synapses 2.2mm

  7. Photoreceptor layer

  8. Photoreceptor has low DC gain, high transient gain

  9. Adaptive Photoreceptor Circuit

  10. Vfb V Vp -UT/e-fold Iphoto log I Vfb Vp

  11. Ib C1 Vout transient Vfb V Vout Vp C2 log I Long term history of brightness V=0 Vfb Vp In steady state (DC)

  12. Bipolar and Horizontal Layer

  13. Vphoto Vphoto Vphoto Vphoto Vphoto Vphoto Vphoto Horizontal cell Averages photoreceptor output Vavg

  14. Vphoto Vphoto Vphoto Vphoto Vphoto Vphoto Vphoto Horizontal cell Averages photoreceptor output Using Deweerth’s follower aggegrator Vavg Transconductance amplifiers

  15. Bipolar Cell Steals center part of diff pair current Rectifies into ON and OFF currents

  16. Ganglion cell layer

  17. Dendritic Trees of Simple Cells Are arranged to make orientation tuned simple cells with push-pull inputs Excitatory Inhibitory

  18. Volume control PCB Chip + Lens Onboard speaker Output selector External speaker jack BNC connector

  19. Spatial RFs of simple cellsMeasured by reverse spike correlation using random orientation stimuli Thanks to Matteo Carrandini

  20. Temporal and spatial frequency tunings of a simple cell Thanks to Matteo Carrandini

  21. Chip design notes • Chip simulation: 1s real time takes about 10h on P3 866MHz (TSPICE) • Simulations are very stiff numerically • Cost: Chip ~$220, system ~$360. (dominated by cost of small quantity chip prototypes)

  22. Specifications

  23. Quick user guide 1

  24. Quick user guide 2 • Things to be careful about: • Watch out for static electricity (ground yourself before picking up the friendchip). Static can kill the chip! • Store the friendchip in an anti-static bag • The lens holder is only attached with double stick tape, it can be pulled off.

  25. What we plan Complex cells Direction selective cells Production of ~100 systems for no-profit distribution to labs and teachers (We have orders for about 30)

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