Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
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noisy. Manysourcesoffluctuationslike,forinstance,synaptictransmissionfailures,channelnoiseand,<br />
mostimportantly,quasirandominputfromotherneuronscontributetothestatisticsofthesubthreshold<br />
membranevoltageandthevariabletimingofneuralspikes(actionpotentials). Usingsimplifiedlinear<br />
andnonlinearintegrate-and-fireneuronmodels,wehavecalculatedthespontaneousfiringandinterspikeintervalstatisticsofneuronsthataresubjectto(i)stochasticadaptation;(ii)short-termsynapticplasticity(synapticfacilitationanddepression);or(iii)stochasticoscillations.Inspecificcases,thesestatistics<br />
allowconclusionsaboutotherwiseinaccessibleparameterslike,forinstance,thenumberofadaptation<br />
channelsinsensoryneurons. Anothercentralproblemofinterestistounderstandhowneuronsencode<br />
time-dependentsignalsintospiketrainsandhowtheircodingpropertiesareinfluencedbyfeatureslike<br />
short-termplasticity,noise,andadaptation. Usinglinearresponsetheory,westudythecodingproblem<br />
indifferentvariantsthatallowtoisolatetheeffectsofacertainfeatureonsignaltransmission.<br />
StochasticDynamicsofHaircells. Onewell-studiedexampleofthetransductionofsensorystimuli<br />
ishearing. Inthemechano-sensoryhaircelloftheinnerearorgansairpressurevariations(sound)are<br />
transducedintoelectricalcurrentsthatcanbetransmittedandprocessedbytheneuronsofthebrain.<br />
Outerhaircellsofthecochlea,however,servealsoanothertask,namely,theactiveamplificationofthe<br />
basilarmembranevibrationinresponsetosoundstimuli. Althoughitiscommonlyacceptedthathair<br />
cellsareanessentialpartoftheactivecochlearamplifier,detailsofthisamplificationarestillpoorly<br />
understoodanddifferenthypothesisarehotlydebated. Thehaircellpossessesasmallorganelle,the<br />
hairbundle,whichisakeyelementinthetransductionandamplificationprocess.Singlehairbundlesin<br />
vitroshowallsignaturesofanactiveamplificationthatare,however,diminishedbyalargeamountof<br />
intrinsicnoise.Inmodelsofdifferentcomplexityaswellasinexperiments,weexplorehowbymeansof<br />
mechanicalhairbundlecouplingthisintrinsicnoisecanbereducedandthusamplificationpropertiesof<br />
thebundlecanbeenhanced.<br />
Diffusionandtransportincells. Transportanddiffusionprocessesareessentialforthefunctioning<br />
ofbiologicalcells.Vesiclesaretransportedalongfilamentsbymeansofmolecularmotorsbutmayalso<br />
suffersubdiffusivemotioninthecytoplasmwhendetachedfromfilaments.Inexperiments,thebehavior<br />
ofvesiclesisoftenexploredbylocalmean-square-displacementanalysis.Westudythepropertiesofthis<br />
algorithmintermsofsimpleLangevinmodels. Anothertopicinthisprojectisthedynamicsofassembliesofmolecularmotors,whichareessentialfortheactivetransportinthecell.<br />
Weinvestigatehow<br />
biophysicalmodelsofmotorassembliescanbeapproximatedbymuchsimplerphenomenologicalmodels<br />
liketheactiveBrownianparticle.<br />
Ongoingcollaborations<br />
Experimentalgroups:<br />
• PascalMartin,<strong>Institut</strong>CurieParis,France<br />
• JanBenda,LMUandBCCNMünchen,Germany<br />
• DorisHeinrich,LMUMünchen,Germany<br />
• IvaTolić-Nørrelykke,MPI-CBGDresden,Germany<br />
• DavidRussellandAlexanderNeiman,OhioUniversity,Athens,USA<br />
Theoreticians:<br />
• AlexanderNeiman,OhioUniversity,Athens,USA<br />
• NenadPavin, mpipksDresden,Germany<br />
• FrankJülicher, mpipksDresden,Germany<br />
• LutzSchimansky-Geier,HUBerlin,Germany<br />
Wehaveanumberofcollaborationswithexperimentalgroupsstudyingthestochasticactivityofand<br />
providinguswithdatafromneurons(BendaandNeiman/Russell)andsensoryhaircells(Martin).Related<br />
theoreticalworkiscarriedouttogetherwithresearchersfromDresden(JülicherandPavin)andAthens,<br />
16 ScientificWorkanditsOrganizationatthe<strong>Institut</strong>e–anOverview