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1、ASiliconAxonBradleyA.Minch,PaulHasler,ChrisDiorio,CarverMeadPhysicsofComputationLaboratoryCaliforniaInstituteofTechnologyPasadena,CA91125bminch,paul,chris,carver@pcmp.caltech.eduAbstractWepresentasiliconmodelofanaxonwhichshowspromiseasabuildingblockforpulse-basedneuralcomputationsinvolv
2、ingcor-relationsofpulsesacrossbothspaceandtime.Thecircuitsharesanumberoffeatureswithitsbiologicalcounterpartincludinganexcitationthreshold,abriefrefractoryperiodafterpulsecomple-tion,pulseamplituderestoration,andpulsewidthrestoration.Weprovideasimpleexplanationofcircuitoperationandprese
3、ntdatafromachipfabricatedinastandard2mCMOSprocessthroughtheMOSImplementationService(MOSIS).Weemphasizethene-cessityoftherestorationofthewidthofthepulseintimeforstablepropagationinaxons.1INTRODUCTIONItiswellknownthataxonsareneuralprocessesspecializedfortransmittinginfor-mationoverrelati
4、velylongdistancesinthenervoussystem.Impulsiveelectricaldisturbancesknownasactionpotentialsarenormallyinitiatednearthecellbodyofaneuronwhenthevoltageacrossthecellmembranecrossesathreshold.Thesepulsesarethenpropagatedwithafairlystereotypicalshapeatamoreorlesscon-stantvelocitydownthelength
5、oftheaxon.Consequently,axonsexcelatpreciselypreservingtherelativetimingofthresholdcrossingeventsbutdonotpreserveanyoftheinitialsignalshape.Information,then,ispresumablyencodedintherelativetimingofactionpotentials.Thebiophysicalmechanismsunderlyingtheinitiationandpropagationofactionpoten
6、tialsinaxonshavebeenwellstudiedsincetheseminalworkofHodgkinandHuxleyonthegiantaxonofLoligo.(Hodgkin&Huxley,1952)Brie
y,whenthevoltageacrossasmallpatchofthecellmembraneincreasestoacertainlevel,apop-ulationofionchannelspermeabletosodiumopens,allowinganin
uxofsodiumions,which,inturn,causes
7、themembranevoltagetoincreasefurtherandapulsetobeinitiated.Thispopulationofchannelsrapidlyinactivates,preventingthepassageofadditionalions.Anotherpopulationofchannelspermeabletopotassiumopensafterabriefdelaycausinganeuxofpotassiumions,restoringthemembranetoamorenegativepotentia
