Electons meet animals


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Electons meet animals

  1. 1. ELECTRONICS MEET ANIMAL BRAIN CHAPTER 1: INTRODUCTIONIntroduction:By enabling better study of animal behaviour‟s neural basis, implantable computers mayrevolutionize field biology and eventually lead to neuralprosthetics, hardware-based human-computer interfaces, and artificial systems that incorporate biological intelligenceprinciples.Recent advances in microelectromechanical systems (MEMS), CMOS electronics, andembeddedcomputersystems will finally let us link computercircuitryto neural cells in liveanimals and, in particular,to reidentifiable cells with specific, knownneuralfunctions. The keycomponents of such abrain-computersystem include neural probes, analogelectronics, and aminiature microcomputer.Researchersdeveloping neural probes such as submicronMEMSprobes, micro clamps, microprobearrays,and similar structures can now penetrateandmakeelectrical contact with nerve cells withoutcausing significant or long-term damage toprobesorcells.Researchers developing analog electronics suchas low-power amplifiers and analog-to-digital converterscan now integrate these devices with microcontrollerson a single low-powerCMOS die.Further,researchers developing embedded computersystems can now incorporate allthe core cir-cuitry of a modern computer on a single silicon chipthat can run on miniscule powerfrom a tiny watch battery. In short, engineers have all the pieces they need to build trulyautonomous implantable computersystems.Untilnow,high signal-to-noise recording as wellasdigital processing of real-time neuronal signalshavebeen possible only in constrainedlaboratoryexperiments.By combining MEMS probes withanalog electronics and modern CMOScomputingintoself-contained, implantable microsystems,implantablecomputers will freeneuroscientistsfromthe lab bench.With advances in integrated circuit processingwill come evermore capable andpower-efficientembedded computers. Thesimple neurochips of today willbecome the complexembedded systems of tomorrow,when embedding in this ultimate sense willmean computerelectronics embedded in nerve tissue.MALLAREDDY COLLEGE OF ENGINEERING 1
  2. 2. ELECTRONICS MEET ANIMAL BRAIN CHAPTER 2: OVERVIEW OF THE PROJECT2.1 Brain machine interfaces (BMIs):BMI‟Soffer a direct path for brain to communicate with outside world, mainly use central neuralactivities to control artificial external devices. These techniques to collect the brain signals couldbe distinguished as non-invasive or invasive BMIs according to the position of recodingelectrodes. Compared with non-invasive BMIs, invasive BMIs have wide potential in assisting,augmenting or repairing more complex motor functions of human, especially in patients withsevere body paralysis. This paper will review our labs research work on invasive BMIs withsubjects on rat and monkey. We built a synchronous recording and analyzing system for ratsneural activities and motor behavior. Rat could use its intention to control external onedimensional robotic lever in real time. Also, a remote control training system was designed torealize rat navigating through 3D obstacle route, as well as switching between “motion” and“motionlessness” at any point during the route. We further extended our work to develop theinvasive BMI system on non-human primate. While the monkey was trained to perform a 2-Dcenter-out task, plenty of neural activities in motor cortex were invasively recorded. We showedthe preliminary decoding results of the 2D trajectory, and plan to utilize the decoded predictionto control an external device, such as robot hand.2.2Integrating silicon and neurobiology:Neurons and neuronal networks decide, remember,modulate, and control an animal‟severysensation,thought, movement, and act. The intimatedetailsof this network, including the dynamicpropertiesof individual neurons and neuron populations,give a nervous system the power tocontrol awidearray of behavioral functions.Thegoal of understanding these detailsmotivatesmanyworkers in modern neurobiology.Tomakesignificantprogress, theseneurobiologists needmethodsfor recording the activity of single neuronsorneuron assemblies, forlong timescales, at highfidelity,in animals that can interact freely with theirsensoryworld andexpress normal behavioural responses.2.3Conventional techniques:Neurobiologists examine the activities of braincells tied to sensory inputs, integrativeprocesses,and motor outputs to understand the neural basisof animal behavior and intelligence.They alsoprobe the components of neuronal control circuitryto understand the plasticity andMALLAREDDY COLLEGE OF ENGINEERING 2
  3. 3. ELECTRONICS MEET ANIMAL BRAINdynamics of control.They want to know more about neuronaldynamicsand networks, aboutsynaptic interactionsbetween neurons, and about the inextricablelinksbetween environmentalstimuli and neuronalsignaling,behavior,and control.To explore the details of this biologicalcircuitry,neurobiologists use two classes of electrodes torecord and stimulate electrical signals intissueintracellular micropipettes to impale or patch-clamp single cells for interrogation of thecell‟sinternal workings, andextracellular wires or micromachined probesfor interrogatingmultisite patterns of extracellularneural signaling or electrical activityinmuscles.Neurobiologistsuse amplifiers and signal generatorsto stimulate and record to and from neurons throughtheseelectrodes, and signal-processing systems toanalyze the results. They have used thesetechniquesfor decades to accumulate a wealth of understandingabout the nervous system.Unfortunately, todate, most of these experiments have been performedon slices of brain tissue oron restrained and immobilizedanimals, primarily because the electronicinstrumentsrequired torun the experiments occupythebetter part of a lab bench.This situation leaves neurobiologistswith a naggingquestion: Are they measuring the animal‟snormalbrain signals or something fardifferent?Further,neurobiologists want to understand howanimalbrains respond and react toenvironmentalstimuli.The only way to truly answer these questionsis to measure a brain‟sneuralsignaling while the animal roams freely in its natural environment.2.4Salient objectives:The solution to these problems lies in making thetest equipment so small that a scientist canimplantit into or onto the animal, using materials andimplantation techniques that hurt neithercomputernor animal. Recent developments in MEMS, semiconductorelectronics, embeddedsystems, biocompatiblematerials, and electronic packagingfinallyallow neuroscientists andengineers to beginpackagingentire neurobiology experiments intohardwareand firmware thatoccupy less space thanahuman fingernail.Researchers call these bioembedded systemsneurochips. Scientists from the University of Washing-ton,Caltech, and Case Western ReserveUniversityhave teamed to build these miniaturized implantableexperimental setups to explore theneural basis ofbehavior.This research effort has developed or is inthe process of developing thefollowing:• miniaturized silicon MEMS probes for recordingfrom the insides of nerve cells;•biocompatible coatings that protect theseprobes from protein fouling;MALLAREDDY COLLEGE OF ENGINEERING 3
  4. 4. ELECTRONICS MEET ANIMAL BRAIN• a stand-alone implantable microcomputer thatrecords from and stimulates neurons,sensorypathways, or motor control pathways in anintact animal, using intracellular probes, extra-cellular probes, or wire electrodes;• Neurophysiological preparations and techniquesfor implanting microchips and wireelectrodesorMEMS probes into or onto animalsin a way that does not damage the probesortissue;•Firmware that performs real-time biologyexperiments with implanted computers,usinganalytical models of the underlying biology;• software to study and interpret the experimentalresults, eventually leading toreverseengineeredstudies of animal behavior.As the “Neuroscience ApplicationExamples”sidebar shows, the first neurochip experiments usesea slugs and moths in artificialenvironments, butbroad interest has already arisen for using implantable computers in manyother animals.a computer was melded with a human brain to create a part-man-part-machinecyborg. Now scientists in New York have created a real-life RoboRat. A rat has had computerchips integrated into its brain, allowingthe machine-mouse to perform seemingly miraculoustasks. For example it can push a lever to get a drink without moving a paw or even a muscle.RoboRat uses its computer implants to manipulate the lever by thought power alone. Thescientists have now created several more RoboRats and they‟ve taken the technology muchfurther. They can send signals to the rats‟ computer implants using a wireless control, and cansteer the rodent as if it were a remote controlled car. When they stimulate its brain one way andthe rodent turns right; when its stimulated another way it turns left. Merging a living mind with amachine may sound like a horrendously cruel creation, but the researchers insist this isn‟t thecase. Indeed they say they have some of the happiest lab rats around - because of the way theytrain them. The rats are not being forced to do anything they don‟t want to do. They turn left orright when the scientists push the buttons on the remote control because they‟ve learnt obeyingthis command results in the pleasure centre of their brains being stimulated by the computer chipimplant. It‟s a bizarre twist on the concept of free will. The researchers haven‟t created RoboRatjust in the pursuit of pure knowledge. Like RoboCop, RoboRat will eventually have importantpublic duties to perform…they could be sent on a rescue mission into the rubble after anEarthquake or building collapse.MALLAREDDY COLLEGE OF ENGINEERING 4
  5. 5. ELECTRONICS MEET ANIMAL BRAIN CHAPTER: 3 BLOCK DIAGRAM3.1 Block Diagram: Fig.3.1 block diagram of neuro chip3.2 A stimulating world:Passive neurochips that do nothing more than record will provide neurobiologists with a wealthof data. But even now, with the first neurochips barely in production, neurobiologists are alreadyMALLAREDDY COLLEGE OF ENGINEERING 5
  6. 6. ELECTRONICS MEET ANIMAL BRAIN calling for designs that stimulate nerve tissue as well as record from it. Active neurochipswill allow stimulus-response experiments that test models of how nervous systems controlbehavior, such as how sensory inputs inform motor-circuit loops and the logic or model behindthe response. Indeed, the neurochip project‟s long-term goal is to develop a hardware andsoftware environment in which a neurobiologist conceives a stimulus-response experiment,encodes that experiment in software, downloads the experiment to an implanted neurochip, andrecovers the data when the experiment concludes. Model of integrative biology in whichneurochips play a key part. Fig.3.2 Flight simulation of mothA Programmable System-on-a-Chip fromCypress MicroSystems integrates amicroprocessor,variable-gain amplifiers, an ADC, a memory controller,and a DAC into a single integrated circuit.First-generationneurochips integrate one ormoreICs,passive elements such as capacitors, batteries,and I/O pads on small micro-PCBs. Theprototypeneurochip used packagedICsand button cells, and occupied a 1 cm ×3 cmprinted-circuitboard. The “production” version,due out of processing in early 2003, uses die-MALLAREDDY COLLEGE OF ENGINEERING 6
  7. 7. ELECTRONICS MEET ANIMAL BRAINonboardtechnology and thin-film batteries, and issmaller than 1 square centimeter. Future-generation neurochips will integrate all the electronicsontoa single silicon chip, and will likely besmallerthan10 mm on a side.3.3 Probes:Building the probes that let a neurochip eavesdropon the electrical signaling in a nervebundle,groupof neurons, or single neuron presents adaunting task. Benchtop experiments onconstrainedanimals typically use metallic needles oftenmade of stainless steel or tungstentocommunicatewith nerve bundles, micromachinedsilicon probes to record from groups ofneurons,or glass capillaries filled with a conductive ionicsolution to penetrate and record fromthe inside ofindividual neurons. In unconstrained animals, flexiblemetallic needles, attached tothe animal withsurgicalsuperglue, and micromachined siliconprobesstill work.However,replicating the performanceof glass capillaries in flying, swimming, wigglinganimals isadifferent story entirely. Fig.3.3 .Micromachined silicon probesSeveral centimeters long and quite fragile, the glasscapillaries that neurobiologists use to probetheinsides of nerve cells typically have tip diameterssmaller than 0.3 microns. They impaleneurons evenmore fragile than the probes themselves. Neurobiologistsuse micromanipulators to painstakinglyandprecisely drive single probes into singleneurons.Fortunately,MEMS technology offers a possiblealternativeto these glass capillaries.University of Washingtonresearchers aredevelopingsilicon MEMS probes and flexibleMALLAREDDY COLLEGE OF ENGINEERING 7
  8. 8. ELECTRONICS MEET ANIMAL BRAINinterconnectstructures to mimic the performance of glasscapillariesin an implantedpreparation.Researchershave already recorded intracellular signals with earlyprototypes, and development is ongoing.3.4Glyme:Researchers seek to implant both probes andneurochips inside an animal‟s brain. Unfortunately,an animal‟s immune system rapidly and indiscriminatelyencapsulates all foreign bodies withproteins,without regard for the research value ofimplantedprobes and neurochips. The adsorbedproteinsnot only attenuate the recorded electricalsignals,but can also jeopardize theanimal‟ssurvivalby causing abnormal tissue growth. Researchers at the University ofWashington‟sCenter for Engineered Biomaterials have developedplasma-deposited ether-terminated oligoethyleneglycol coatings that inhibit protein fouling, asPreliminary researchindicates thatthese glyme coatings can reduce the protein fouling of probes and neurochips to levelsacceptable for week-long experiments.3.5 The power struggle:Neurochips can derive power from onboard batteries,external radiofrequency sources, awiretether, or the nerve tissue itself. The ultimate decision on the power source depends on thenature oftheexperiments and the animal‟senvironment.Batteriesare attractive because they avoidthe antennasand charge pumps required to capture RFenergy,operate in all environments, do notrestricttheanimal‟smovement the way a tether does, andprovidemuch more power than tappingnerve cellsforenergy.Batteries have a weight disadvantage, but thinfilmtechnologies usingLiCoO2/LiPON/Li andNi/KOH/Znpromise flexible rechargeable batterieswith peak currentdensities greater than 12 mApersquare centimeter for short-duration experiments,and lifetimesmeasured in days or longer atlow-currentdensities.7,8Batteries are ideal for the two sample preparationsshown in the “Neuroscience ApplicationExamples”sidebar.The typical hawkmoth flighttimeis less than 60 seconds. The 12 mAprovidedbya 200 mg, one-square-centimeter battery easilypowersa neurochip for thisexperiment‟sduration.Thesea slug trolling methodically along theseafloorlies at the opposite endof the spectrum,needingonly a few milliamps of current to poweraneurochip for a week. The slugcan easily accom-modate a large battery in its visceral cavity, allow-ing extended untetheredexperiments.MALLAREDDY COLLEGE OF ENGINEERING 8
  9. 9. ELECTRONICS MEET ANIMAL BRAIN3.6 Memory:Once implanted, an embedded neurochip mustread its experimental procedure from memory,runthe experiment, acquire the neural spike trains, thenstore the results in memory. As with allcomputersystems, memory size is an issue for neurochips.Fortunately, the electrical spike trainsgenerated bynerve tissue have a stereotyped shape as shown, suggesting that neurochips shouldcompressthe neural waveforms before storing them inmemory.Compressingthe signals has twoadvantages. Fig.3.4 flash memory on pcbFirst,it effectively increases the onboard storagecapacity. Second, it decreases the frequencyofmemory writes, reducing power consumption.Even simple compression algorithms such asrunlengthencoding can achieve better than 10 to 1compressionratios on neural signals.Customalgorithms that apply vector quantization,run-length encoding, and Huffmanencodingtodifferent parts of the neural waveform canachieveup to 1,000 to 1 compressionratios.Giventhe limited computing power of an implantablemicrocomputer, simpler is better when it comestocompression, but even simple RLE offers huge.MALLAREDDY COLLEGE OF ENGINEERING 9
  10. 10. ELECTRONICS MEET ANIMAL BRAIN CHAPTER 4: DESIGNER CHIPS4.1 Designer Neurochips:Like their bench top experimental counterparts,neurochips use amplifiers to boost low-voltagebiological signals, analog-to-digital converters(ADCs) to digitize these signals,microcomputersto process the signals, onboard memory to storethe signals, digital-to-analogconverters (DACs)to stimulate nerves, and software to control theoverall experiment.The keyrequirements are that the neurochip be smalland lightweight enough to fit inside or onto theanimal, have adequate signal fidelity for interactingwiththe millivolt-level signals characteristicofnerve tissue, and have sufficient processing powertoperform experiments of real scientificvalue.The basic components of a neurochip are commerciallyavailable today. They includeinstrumentation amplifiers, ADCs/DACs, reconfigurablemicrocomputers, and high-densitymemory.4.2MSP430 Microcontrollers (MCUs):From Texas Instruments (TI) are 16-bit, RISC-based, mixed-signal processors designedspecifically for ultra-low-power. MSP430 MCUs have the right mix of intelligent peripherals,ease-of-use, low cost and lowest power consumption for thousands of applications – includingyours. TI offers robust design support for the MSP430 MCU platform along with technicaldocuments, training, tools and software to help designers develop products and release them tomarket faster.Ultra-Low PowerThe MSP430 MCU is designed specifically for ultra-low-power applications. Its flexibleclocking system, multiple low-power modes, instant wakeup and intelligent autonomousperipherals enable true ultra-low-power optimization, dramatically extending battery life.Flexible Clocking SystemThe MSP430 MCU clock system has the ability to enable and disable various clocks andoscillators which allow the device to enter various low-power modes (LPMs). The flexibleMALLAREDDY COLLEGE OF ENGINEERING 10
  11. 11. ELECTRONICS MEET ANIMAL BRAINclocking system optimizes overall current consumption by only enabling the required clockswhen appropriate. Fig.4.1 cyborg beetleEasy to Get StartedMSP430 MCUs are easy-to-use because of a modern 16-bit RISC architecture and a simpledevelopment ecosystem.16-Bit Orthogonal ArchitectureThe MSP430 MCU‟s 16-bit architecture provides the flexibility of 16 fully-addressable, single-cycle, 16-bit CPU registers with the power of a RISC. The modern design of the CPU offersversatility using only 27 easy-to-understand instructions and seven consistent addressing modes.MALLAREDDY COLLEGE OF ENGINEERING 11
  12. 12. ELECTRONICS MEET ANIMAL BRAIN Fig.4.2 block diagram of MSP430 MC CHAPTER 5: APPLICATIONSWiring a sea slug:Beneath a research vessel anchored in thePuget Sound, two scientists clad in scuba gear hoverover the bright orange sea slug. From the outside, this slug lookslike any other. But thisparticular slug has abattery-powered microcomputer implantedin its brain and minuscule siliconneedles communicatingwith its neurons. The microcomputerfaithfully performs a biologyexperimentas the animal goes about its normalbehavior.Meanwhile, the scientists videotape theslug‟s feeding, fleeing, and social behaviorswhile measuring water currents andgeomagneticfields. Later,these scientists will studytheenvironmental measurements andelectronicrecordings in an attempt to decode howtheslug‟sbrain patterns correlate withbehavior.The anticipated outcome: groundbreakingfindings in behavioral neurobiology.Monitoring a moth’s flight controlsIn a small, dark zoology lab, a giant mothperforms an aerial ballet as it feeds from aroboticallycontrolled artificial flower, unawarethat the flower‟smovements are programmedto test themoth‟sflight dynamics.Theultra-high-speed infrared video recordertapesthe moth‟severymovement.But the special part of this experiment isneither the flower nor the videotaping. Itisthe tiny battery-powered microcomputerattached to the moth‟s thorax that recordselectricalsignals from the flight muscles andsense organs and stores this data in onboardmemory.Robo-Rats Hunt LandminesRats with brain implants that turn them into remote controlled drones could soon be unleashedon the countryside of Colombia as a secret weapon to combat deadly landmines planted by rebelsand drug lords.The „robo-rats‟ were created by top American brain scientist doctor John Chapin shortly after9/11 when it became clear rescue dogs were inadequate to search the rubble of the World TradeCentre. Unfortunately, technical challenges kept the robo-rats from being finished in time to lookfor survivors.MALLAREDDY COLLEGE OF ENGINEERING 12
  13. 13. ELECTRONICS MEET ANIMAL BRAIN CHAPTER 6: FUTURE SCOPE Even as the first miniature neurochips record neuronal action potentials,researchers at theUniversity of Washingtonare testing stimulus paradigmsto evoke controlled muscular extensionand contraction.Rather than driving the muscles directly using high-resolution voltagestimuluswaveforms generated by digital synthesis and a digital-to-analogconverter, they tried stimulatingnerve bundles instead, using simple digitalwaveforms directly.They derived pulse-widthmodulated signalsdirectlyfrom logic gates, and drove these waveforms into the nerve bundlesthatenervate the muscles.Early results show great promise, not only because the techniqueactuallyworked, but because a microcontroller can easily generate digitalpulses, and the drivecurrents needed for nerve stimulation are up to 100timessmaller than those needed to drivemuscle tissue directly.This powersavingswill allow functional stimulation by miniatureneurochips. Next on the research agenda: statistical machine learning. Researchersalready plan to usesmart algorithms, smart software, and smart chips tointeract dynamically with nerve tissue. Theysuspect that machine learning can help them study the cause-and-effect relationships involved inthebehavior of sensory motor circuits. Beyond that, they won‟t speculate,but the applications ofthis neurochip research to robotics, medical prosthetics,and a host of other applications seemobvious.MALLAREDDY COLLEGE OF ENGINEERING 13
  14. 14. ELECTRONICS MEET ANIMAL BRAIN CHAPTER7: REFERENCES  M.R. Enstrom et al., “Abdominal Ruddering and the Control of Flight in the Hawkmoth,” to be published, 2003; www.sicb.org/meetings/2003/schedule/ abstractdetails.php3?id=758.  http://www.meritummedia.com/world/robo-rats-hunt-landmines  http://www.instrumentationtoday.com/mems-accelerometer/2011/08/  http://homes.cs.washington.edu/~diorio/Publications/InvitedPubs/01160058_IEEEComp.pdfMALLAREDDY COLLEGE OF ENGINEERING 14