From rkmishra from cbcs.ac.in Wed Apr 1 01:48:46 2009 From: rkmishra from cbcs.ac.in (Ramesh Mishra) Date: Wed Apr 1 12:21:33 2009 Subject: [Neuroscience] International Conference on Language and Cognition Message-ID: <939e39190903312348o2315f1f7t6026612ebee06c@mail.gmail.com> *International Conference on Language =96Cognition Interface: State of the Art* *at* *Centre for Behavioural and Cognitive Sciences (CBCS)* *University of Allahabad* *September 24-26 2009* * * The Centre of Behavioural and Cognitive Sciences har organized major international conferences in the past six years. Last year, the Centre succesfully organized an International Conference on Attention in December. This year, the Centre is organizing an international conference on Language =96Cognition Interface: State of the Art. Research on language in its various manifestations continues to remain a major area in cognitive science research with ever increasing sophistication in methodology and theory. The relationship of language to thinking and cognition as well as to consciousness is central to any understanding of human cognition. Integration and consolidation of researc= h is important for gaining insights and broadening discourse as well as for future research direction. The aim of the proposed three days international conference is to invite researchers from both India and abroad including younger scholars in the area of language and cognition to CBCS for focused discussion and exchanges of ideas on current research in several interface areas. The conference will have selected speakers for oral talks and poster presentations by research students and young scientists. *Areas of interest* Sentence processing Neurolinguistics Multi-modal interaction in language processing Computational linguistics and NLP Electrophysiology and neuroimaging studies of speech-language processing Language and knowledge representation Formal theories of language and cognition Cognitive Linguistics *Call for Abstracts* PhD students and young researchers are invited to submit detailed abstracts (500 words) by June 30th for consideration. Selected abstracts will be funded for participation and will be presented only as posters. Kindly send your abstracts to the following email address (office@cbcs.ac.in or rkmishra@cbcs.ac.in) as a word attachment by June 30th 2009. *Venue* The conference will be held at Centre for Behavioural and Cognitive Sciences, Allahabad University. * * *Organizing Committee* Prof. R.G. Harshe (Chair) Prof. Narayanan Srinivasan (Co-convenor) Dr Bhoomika Kar Dr. Chandrasekhar Pammi Dr.Ramesh Kumar Mishra (Co-convenor) Please contact Dr. Ramesh Kumar Mishra (rkmishra@cbcs.ac.in), the co-convenor and organizing secretary of the conference for further information. --=20 Ramesh Kumar Mishra PhD Centre for Behavioural and Cognitive Science ( CBCS) University of Allahabad Allahabad 211002 India Email:rkmishra@cbcs.ac.in Ph-91-0532-2460738 ( work) Mob-91-9451872007 Fax-91-0532-2460738( work) http://www.cbcs.ac.in/~rkmishra.htm From arin280 from gmail.com Thu Apr 2 13:50:06 2009 From: arin280 from gmail.com (Ben) Date: Thu Apr 2 15:25:36 2009 Subject: [Neuroscience] A Useful Website for Neuroscience Researchers - MyNetResearch.com Message-ID: <9e295ebd-cf38-4c2b-94c7-eca9a088ad4e@g20g2000vba.googlegroups.com> Dear Neuroscience Researcher, With a team of academics, I recently launched the research website, MyNetResearch.com. Our website helps researchers to increase their research productivity. Specifically, the website enables you to: - manage your research papers and grant proposals online and access them from any location - conduct online surveys and citation searches - receive expert advice on research and statistical design - read about the latest research in hundreds of different subjects - exchange ideas with thousands of other researchers - collaborate with thousands of other researchers on your research papers Currently, over 5,600 researchers from 95 countries and multiple research specialties use MyNetResearch for their research activities. I=92m trying to spread the word about MyNetResearch and to let academic researchers know about this great resource. Regular membership is completely free. I invite you to try MyNetResearch. You can sign up at: https://www.mynetresearch.com/Signup/SignUp.aspx Sincerely, Bay Arinze, Ph.D., Founding Editor MyNetResearch, Empowering Collaboration=99 From connelly.bill from gmail.com Thu Apr 2 19:25:34 2009 From: connelly.bill from gmail.com (Bill) Date: Thu Apr 2 21:17:27 2009 Subject: [Neuroscience] Equation that explains the behaviour of a circuit in voltage clamp Message-ID: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> Hi, I've already satisfied myself that the function to explain the behaviour of a neuronal membrane (in current clamp) is dV/dt = I/C where I is the sum of all transmembrane currents But what is the equation for a membrane under voltage clamp? That is how does one explain the behaviour of the holding current I, in response to membrane capacitance and changes in membrane conductances? Thanks for any help. From r_sn_orman from comcast.net Thu Apr 2 20:16:51 2009 From: r_sn_orman from comcast.net (r norman) Date: Thu Apr 2 21:17:30 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> Message-ID: On Thu, 2 Apr 2009 17:25:34 -0700 (PDT), Bill wrote:+++ >Hi, > >I've already satisfied myself that the function to explain the >behaviour of a neuronal membrane (in current clamp) is >dV/dt = I/C where I is the sum of all transmembrane currents > >But what is the equation for a membrane under voltage clamp? That is >how does one explain the behaviour of the holding current I, in >response to membrane capacitance and changes in membrane conductances? > >Thanks for any help. I don't have my copy of Hodgkin/Huxley (1952) with me at the moment, but that is exactly where you must begin. Here, to my recollection, is how it goes: Iclamp = Imembrane because any longitudinal current is eliminated by space clampl Imembrane = Icap + Iionic because those are the only two ways current can cross the membrane. Icap = C dV/dt = 0 because during voltage clamp, the voltage is ordinarily constant. Of course, there is an enormous transient capacitative current at the time of the voltage step. Iionic = INa + IK + Ileak because some ion has to carry the current and Na and K are ordinarily the only significant players. Any chloride current is hidden in the "leak". So that reduces to Iclamp = INa + IK + Ileak. Now throw in INa = gNa(Vm - ENa), IK = gK(Vm - EK) and Ileak = gLeak(Vm = Eleak) where the ENa, EK and Eleak are the Nernst equilibrium potentials dependent only on concentration, hence constant during the clamp. You now have the clamp current as a function of membrane potential and membrane conductances. Once again, during the clamp the membrane potential is ordinarily constant. Therefore, any changes in clamp current during the clamp must necessarily be the result of changes in membrane conductance. The trick now is to separate the total current into the separate ionic components so you can study the separate ionic conductances; the behavior of the ion channels. From connelly.bill from gmail.com Thu Apr 2 23:04:39 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Fri Apr 3 11:26:20 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> Message-ID: Thanks, > Icap = C dV/dt = 0 because during voltage clamp, the voltage is > ordinarily constant. Of course, there is an enormous transient > capacitative current at the time of the voltage step. Aah, that is exactly where I am having the issue. What happens during the voltage step. Now I appreciate at the point of the step, dV/dt = infinity (or close enough), so Icap is infinity, and the capcitor fills instantly. However, because of the series resistance of the electrode, peak delta I = delta V * Rs. But this is where I fall over. Because what happens during Non-step voltages (ramps etc). I also get that in a parallel RC circuit Itot = V/Rm + C * dV/dt But that leaves me in the same position, with dV/dt = infinity. So it needs some kind of modifier, but I can't figure it out. From r_s_norman from comcast.net Fri Apr 3 09:32:09 2009 From: r_s_norman from comcast.net (r norman) Date: Fri Apr 3 11:26:36 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> Message-ID: On Thu, 2 Apr 2009 21:04:39 -0700 (PDT), "Bill.Connelly" wrote: >Thanks, > >> Icap = C dV/dt = 0 because during voltage clamp, the voltage is >> ordinarily constant. Of course, there is an enormous transient >> capacitative current at the time of the voltage step. > >Aah, that is exactly where I am having the issue. What happens during >the voltage step. Now I appreciate at the point of the step, dV/dt = >infinity (or close enough), so Icap is infinity, and the capcitor >fills instantly. However, because of the series resistance of the >electrode, peak delta I = delta V * Rs. But this is where I fall over. >Because what happens during Non-step voltages (ramps etc). > >I also get that in a parallel RC circuit > >Itot = V/Rm + C * dV/dt > >But that leaves me in the same position, with dV/dt = infinity. So it >needs some kind of modifier, but I can't figure it out. You just accept that there is an enormous spike of capacitative current that the equipment can handle and recover from quickly. If course it is not infinite, but if you integrate the very large current over the very short duration of the interval, you get the total charge necessary to change the voltage by the step, Cm times the step voltage. The capacitative current is so large that it is "off screen" and doesn't show in the clamp records except as a very short gap. My impression of the history is that K.C. Cole, who actually invented the voltage clamp, worried that the "backwards" inward current flow immediately after the step was some sort of instrumental artifact resulting from that enormous capacitative current spike and spent a tremendous amount of time trying to figure out if it was real or not. Hodgkin and Huxley, on the other hand, used Cole's idea of the circuitry but didn't worry about it and just accepted the results as real. They then went on to show that that inward component was the Sodium inrush and the rest (including Nobel Prizes) is history. Certainly Cole would have done the same thing, but just a little while later. If you use non-step clamp voltages, you just calculate the dV/dt term and subtract the capacitative component from the total current to get the pure ionic component. It is not hard to measure the capacitance. For a ramp it is very simple because dV/dt is constant during the ramp. Again, any variation in current must be caused by variation in ion conductance. From connelly.bill from gmail.com Sat Apr 4 04:34:37 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sat Apr 4 11:35:30 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> Message-ID: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> On Apr 4, 3:32?am, r norman wrote: > If you use non-step clamp voltages, you just calculate the dV/dt term > and subtract the capacitative component from the total current to get > the pure ionic component. Well this is exactly where I am stuck, how do I calculate the current that "crosses" the capcitor, I know its somehow proportional to the series resistor, the membrane capacitance and dV/dt, but exactly how, I'm not sure. From r_s_norman from comcast.net Sat Apr 4 10:26:04 2009 From: r_s_norman from comcast.net (r norman) Date: Sat Apr 4 11:35:36 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: On Sat, 4 Apr 2009 02:34:37 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 4, 3:32?am, r norman wrote: > >> If you use non-step clamp voltages, you just calculate the dV/dt term >> and subtract the capacitative component from the total current to get >> the pure ionic component. > >Well this is exactly where I am stuck, how do I calculate the current >that "crosses" the capcitor, I know its somehow proportional to the >series resistor, the membrane capacitance and dV/dt, but exactly how, >I'm not sure. Icap = C dV/dt The resistance (conductance) is not involved. C is a constant, easily measured. V(t) is known, hence dV/dt is known. From I.Vida from bio.gla.ac.uk Sat Apr 4 12:06:53 2009 From: I.Vida from bio.gla.ac.uk (Imre Vida) Date: Sat Apr 4 18:45:34 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp In-Reply-To: References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: <20090404170653.GE3056@bio.gla.ac.uk> On Sat, Apr 04, 2009 at 08:26:04AM -0700, r norman wrote: > On Sat, 4 Apr 2009 02:34:37 -0700 (PDT), "Bill.Connelly" > wrote: > > >On Apr 4, 3:32?am, r norman wrote: > > > >> If you use non-step clamp voltages, you just calculate the dV/dt term > >> and subtract the capacitative component from the total current to get > >> the pure ionic component. > > > >Well this is exactly where I am stuck, how do I calculate the current > >that "crosses" the capcitor, I know its somehow proportional to the > >series resistor, the membrane capacitance and dV/dt, but exactly how, > >I'm not sure. > > Icap = C dV/dt > > The resistance (conductance) is not involved. > C is a constant, easily measured. V(t) is known, hence dV/dt is > known. it is the other way around: the dV/dt is defined by the current flowing through the capacitor and the current is defined by the series resistance: At the moment when the voltage step (Vp) is applied (or switched off), all the current flows through the membrane capacitor, the membrane impedance is ~0 and the full voltage drop occurs across the series resistance. The current is calculated as Vp/Rs (actually, one measures the initial peak I and calculate Rs as Vp/I) As the membrane C is charging up, the voltage drop across Rs is decreasing and the total current flowing through the pipette into the cell (and across the membrane) will be reduced. At the same time, as the membrane potential changes, larger and lager part of the current will flow through the resistive elements and smaller and smaller current will be charging the capacitor. In steady state, all current flows through the membrane resistance (Rin, "input resistance" of the cell). The current will be Vp/(Rs+Rin) and the dV on the membrane is Vp*Rm/(Rs+Rm). We often assume that dV=Vp but this is valid only if Rs is negligibly small compared to Rin. I hope this helps imre From connelly.bill from gmail.com Sat Apr 4 16:57:34 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sat Apr 4 18:46:21 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: On Apr 5, 3:26?am, r norman wrote: > Icap = C dV/dt > > The resistance (conductance) is not involved. > C is a constant, easily measured. ? V(t) is known, hence dV/dt is > known. But that can't be right, because that in response to a step, where dv/ dt = infinity, Icap = ifinity. But in reality it's Rs*V. It's the pressence of Rs that is screwing everything up. if it isn't for Rs, the current can be explained as Itot = V/Rm + C dV/dt From r_s_norman from comcast.net Sat Apr 4 17:51:49 2009 From: r_s_norman from comcast.net (r norman) Date: Sat Apr 4 18:46:25 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: On Sat, 4 Apr 2009 14:57:34 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 5, 3:26?am, r norman wrote: > >> Icap = C dV/dt >> >> The resistance (conductance) is not involved. >> C is a constant, easily measured. ? V(t) is known, hence dV/dt is >> known. > >But that can't be right, because that in response to a step, where dv/ >dt = infinity, Icap = ifinity. But in reality it's Rs*V. It's the >pressence of Rs that is screwing everything up. if it isn't for Rs, >the current can be explained as Itot = V/Rm + C dV/dt We have been over this. The current is not infinite because the step does not have an infinitely steep rise. It takes a certain time for the voltage to change from one level to another, a very short time, and during that time there is a very large capacitative current flowing. If you have significant series resistance, then you do not have a good voltage clamp. Ideally, you should measure the voltage with different electrodes than the ones you use to pass current. If there is significant series resistance then you must estimate its value and sutract out I times Rs from the voltage where I is the total current. Whether or not there is Rs, the membrane current is still Im = V/Rm + C dV/dt where V is the true transmembrane voltage, not a measured voltage contaminated by the I * Rs term. From connelly.bill from gmail.com Sat Apr 4 20:30:36 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sat Apr 4 22:08:25 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: On Apr 5, 10:51?am, r norman wrote: > On Sat, 4 Apr 2009 14:57:34 -0700 (PDT), "Bill.Connelly" > Whether or not there is Rs, the membrane current is still Im = V/Rm + > C dV/dt where V is the true transmembrane voltage, not a measured > voltage contaminated by the I * Rs term. Ohhhhh... okay then.... So Im = Vm/Rm + C dVm/dt And Vm... well dVm/dt=(Vcmd-Vm)/(Rs*Cm) No, that still isn't right, because Vm tends absolutely towards Vcmd. Somehow I need to take into account Im*Rs I'm sorry I'm being stupid here. I'm trying to grasp what you're saying, I'm just not very good at the math and the physics. From connelly.bill from gmail.com Sat Apr 4 20:40:50 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sat Apr 4 22:08:31 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: <0ab134cd-c822-4add-8cde-5bf6cdd7be47@j9g2000prh.googlegroups.com> Hi Imre, >and the dV on the membrane is Vp*Rm/(Rs+Rm). We often assume that > dV=Vp but this is valid only if Rs is negligibly small compared to > Rin. Wait, is that dV, or is that just the steady state value of Vm, i.e. Rs and Rm are acting as a voltage divider. Assuming a neglible Rs, dVm/dt=(Vcmd-Vm)/(Rs*Cm). Maybe, to include Rs, it should be dVm/dt=(Vcmd-Vm-Vs)/(Rs*Cm). Where Vs is the voltage over Rs, which is Itot*Vs ? On Apr 5, 1:30?pm, "Bill.Connelly" wrote: > On Apr 5, 10:51?am, r norman wrote: > > > On Sat, 4 Apr 2009 14:57:34 -0700 (PDT), "Bill.Connelly" > > Whether or not there is Rs, the membrane current is still Im = V/Rm + > > C dV/dt where V is the true transmembrane voltage, not a measured > > voltage contaminated by the I * Rs term. > > Ohhhhh... okay then.... So > > Im = Vm/Rm + C dVm/dt > And Vm... well > dVm/dt=(Vcmd-Vm)/(Rs*Cm) > > No, that still isn't right, because Vm tends absolutely towards Vcmd. > > Somehow I need to take into account Im*Rs > > I'm sorry I'm being stupid here. I'm trying to grasp what you're > saying, I'm just not very good at the math and the physics. From connelly.bill from gmail.com Sat Apr 4 20:42:32 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sat Apr 4 22:08:35 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <8583a4b1-53c5-4188-ba90-c7f498fc15b1@f41g2000pra.googlegroups.com> <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> <0ab134cd-c822-4add-8cde-5bf6cdd7be47@j9g2000prh.googlegroups.com> Message-ID: <9fa3415d-ba84-472c-8ab0-ac74ac845fd8@v23g2000pro.googlegroups.com> On Apr 5, 1:40?pm, "Bill.Connelly" wrote: > Maybe, to include Rs, it should be > dVm/dt=(Vcmd-Vm-Vs)/(Rs*Cm). > Where Vs is the voltage over Rs, which is Itot*Vs > ? > No, I'm an idiot, ignore that. From r_s_norman from comcast.net Sun Apr 5 01:14:11 2009 From: r_s_norman from comcast.net (r norman) Date: Sun Apr 5 12:23:30 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: <5migt4hom55g190paa0igorqnr10ec3l41@4ax.com> On Sat, 4 Apr 2009 18:30:36 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 5, 10:51?am, r norman wrote: >> On Sat, 4 Apr 2009 14:57:34 -0700 (PDT), "Bill.Connelly" > >> Whether or not there is Rs, the membrane current is still Im = V/Rm + >> C dV/dt where V is the true transmembrane voltage, not a measured >> voltage contaminated by the I * Rs term. > >Ohhhhh... okay then.... So > >Im = Vm/Rm + C dVm/dt >And Vm... well >dVm/dt=(Vcmd-Vm)/(Rs*Cm) > >No, that still isn't right, because Vm tends absolutely towards Vcmd. > >Somehow I need to take into account Im*Rs > >I'm sorry I'm being stupid here. I'm trying to grasp what you're >saying, I'm just not very good at the math and the physics. We may be talking about different things here. I am assuming you have a series resistance, Rs, in series with a parallel combination of membrane resistance, Rm, and membrane capacitance, C. The current through the series resistance is necessarily exactly the same current that flows through the parallel circuit of the membrane and is both membrane current and clamp current. The membrane current is, as already described, Vm/Rm + C dVm/dt. the voltage across the entire thing is IRs + Vm. You should be able to measure Rs. You also measure I. Therefore you can calculate I Rs. You know the clamp voltage. Therefore you can calculate Vm. And you can calculate dVm/dt. You should be able to measure C. Therefore you can calculate C dVm/dt. Therefore you should be able to calculate Iionic = Vm/Rm. You already calculated Vm so you should be able to calculate Rm = 1/gm. That is, from the voltage clamp data you should be able to see the membrane conductances change. Also knowing Iionic, you should be able to separate that into its components, INa and IK using the same tricks Hodgkin and Huxley used. From connelly.bill from gmail.com Sun Apr 5 03:29:16 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sun Apr 5 12:23:36 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> Message-ID: <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> I appriciate the technical limitations of ACTUALLY performing voltage clamp, it's just I was hoping to get an equation that relates dVcmd/dt to Itotal, on the basis of Rm, Rs and Cm. I'm starting to assume such an equation doesn't exist. If you think it does, I would deeply appriciate if you could give it to me. But some people think you can't analytically explain I for any arbitraty Vcmd. http://www.physicsforums.com/showthread.php?p=2144713#post2144713 http://www.physicsforums.com/attachment.php?attachmentid=18292&d=1238839219 But I completely agree I=Vm/Rm + C dVm/dt. the voltage across the entire thing is (Vcmd).... Vcmd = IRs + Vm. But what explains Vm? Ohh... so So its Vm=Vcmd - Rs * Vm/Rm+C dVm/dt Is that right? And is that even solveable? From r_s_norman from comcast.net Sun Apr 5 01:23:58 2009 From: r_s_norman from comcast.net (r norman) Date: Sun Apr 5 12:23:46 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> Message-ID: <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> On Sat, 4 Apr 2009 18:30:36 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 5, 10:51?am, r norman wrote: >> On Sat, 4 Apr 2009 14:57:34 -0700 (PDT), "Bill.Connelly" > >> Whether or not there is Rs, the membrane current is still Im = V/Rm + >> C dV/dt where V is the true transmembrane voltage, not a measured >> voltage contaminated by the I * Rs term. > >Ohhhhh... okay then.... So > >Im = Vm/Rm + C dVm/dt >And Vm... well >dVm/dt=(Vcmd-Vm)/(Rs*Cm) > >No, that still isn't right, because Vm tends absolutely towards Vcmd. > >Somehow I need to take into account Im*Rs > >I'm sorry I'm being stupid here. I'm trying to grasp what you're >saying, I'm just not very good at the math and the physics. Why don't you read up on "single electrode voltage clamp", as in http://www.scholarpedia.org/article/Single_electrode_voltage_clamp I have been describing the techniqyue for what is there called "continuous single-electrode clamp" or cSEVC. It requires the Rs be small or that the current be small. It also requires that Rs be constant and linear, something that is not at all true if it results from a microelectrode. If none of that is true, then you really need to consider the discontinuous technique, dSEVC, which is described in some detail in that citation. Or else you need to use a two electrode clamp, one electrode for passing current, the other for measuring voltage. That eliminates the series resistance problem. From r_s_norman from comcast.net Sun Apr 5 10:16:47 2009 From: r_s_norman from comcast.net (r norman) Date: Sun Apr 5 12:23:51 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> Message-ID: On Sun, 5 Apr 2009 01:29:16 -0700 (PDT), "Bill.Connelly" wrote: >I appriciate the technical limitations of ACTUALLY performing voltage >clamp, it's just I was hoping to get an equation that relates dVcmd/dt >to Itotal, on the basis of Rm, Rs and Cm. I'm starting to assume such >an equation doesn't exist. If you think it does, I would deeply >appriciate if you could give it to me. But some people think you can't >analytically explain I for any arbitraty Vcmd. >http://www.physicsforums.com/showthread.php?p=2144713#post2144713 >http://www.physicsforums.com/attachment.php?attachmentid=18292&d=1238839219 > >But I completely agree >I=Vm/Rm + C dVm/dt. >the voltage across the entire thing is (Vcmd).... Vcmd = IRs + Vm. >But what explains Vm? >Ohh... so >So its Vm=Vcmd - Rs * Vm/Rm+C dVm/dt > >Is that right? And is that even solveable? Yes, if you have actual data. Your final equation is wrong, that is the problem. Vcmd = I Rs + Vm -- you have this correct. Now just write Vm = Vcmd - I Rs. When doing a voltage clamp, you get a plot (or a data listing) of I vs. t and of Vcmd vs t. So if you know Rs, you can easily calculate Vm. The first post you cite says : "However, I want to be able to calculate I and any time, in response to an arbitrary voltage." That is the problem. You dont CALCULATE I, you MEASURE it in a voltage clamp. There is no way in general to calculate it for a real membrane because the membrane is active and Rm (or gm) changes as a function of V. From connelly.bill from gmail.com Sun Apr 5 16:52:11 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Sun Apr 5 17:51:09 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <82acd914-de9a-46c9-b14e-c36306b6771a@s12g2000prc.googlegroups.com> <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> Message-ID: On Apr 6, 3:16?am, r norman wrote: > Vcmd = I Rs + Vm ?-- you have this correct. > > Now just write ? ?Vm = Vcmd - I Rs. And as I = Vm/Rm + C dVm/dt, then Vm = Vcmd - (Vm/Rm + C dVm/dt) * Rs. From r_s_norman from comcast.net Mon Apr 6 01:13:23 2009 From: r_s_norman from comcast.net (r norman) Date: Mon Apr 6 09:13:01 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> Message-ID: On Sun, 5 Apr 2009 14:52:11 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 6, 3:16?am, r norman wrote: > >> Vcmd = I Rs + Vm ?-- you have this correct. >> >> Now just write ? ?Vm = Vcmd - I Rs. > >And as I = Vm/Rm + C dVm/dt, then >Vm = Vcmd - (Vm/Rm + C dVm/dt) * Rs. That gives you a differential equation you can solve for Vm knowing Vcmd. BUT..... The real question is just why are you doing all this algebra (and calculus)? Are you really interested in voltage clamp on real cells? What type of cell, what type of activity? A real cell is NOT a passive RC circuit. Any interesting cell has active spots, whether synaptic or electrically excitable in which case Rm varies outside your control. The usual purpose of voltage clamping is so you can study just how Rm (more usually written 1/Rm = gm) varies with Vm and with time. When Rm changes, you can NOT solve the equation you just wrote down. So just what are you after with all these voltage clamp questions? Are you actually attempting to do voltage clamp experiments or are you trying to solve homework problems? From sdouglas75 from btinternet.com Mon Apr 6 12:12:35 2009 From: sdouglas75 from btinternet.com (SARAH DOUGLAS) Date: Mon Apr 6 15:12:47 2009 Subject: [Neuroscience] sinasitus! Message-ID: <32250.61047.qm@web87105.mail.ird.yahoo.com> Don't know who you are or why this thread is up but I found it interesting enough to reply so I hope it's not a waste of time. I'm just replying to a thread that I happen to come accross.? http://www.bio.net/bionet/mm/neur-sci/1996-July/024600.html It just so happens that I have regular colds and always have done since I was little.? I'm going though a pretty bad one at the moment and everything seems to be linked to my nose, throat and ears.? I'm already partically deaf and I'm also dyslexic. maybe you can get back to me. Sarah-Lou From connelly.bill from gmail.com Tue Apr 7 20:50:31 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Wed Apr 8 08:48:53 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> Message-ID: <6b1d01f3-49f1-4873-87e4-fc082c948e62@c9g2000yqm.googlegroups.com> On Apr 6, 6:13?pm, r norman wrote: > Are you actually attempting to do voltage clamp experiments or are you > trying to solve homework problems? More general curiosity than anything. What I was REALLY trying to do was understand the behaviour of the op amp circuitry of your basic headstage, i.e. the current to voltage converter and then the differential amp that subtracts Vcmd. I thought I needed to know the equation for the feedback current, but I didn't. I was trying to prove to myself that even with a significant series resistance, the op amp circuitry still behaved properly (even if it doesn't clamp the cell properly). I've gotten quite obsessive about trying to understand every detail about e-phys recently. I was at a neuroscience course, where a lot of the other students (some of whom were post docs and had far 'fancier' papers than I do, doing whole-cell voltage clamp) really had no idea about what they were actually doing during voltage clamp. They just kinda assumed that the entire cell was clamped exactly where they set the dial on the preamp, and the reported current was exactly equal to the transmembrane current. It just kinda reminded me of how anyone can be taught to use a calculator, and 9 times out of 10, they'll get the right answer, but if they don't understand math, that 10th time, when they times 2 by 2, and they get 46873, they wont think it is odd. It was really quite interesting looking back on Hodgkin and Huxley's papers, when they 'invented' series resistance compensation... and the resistance they were compensating for was only a couple of kiloOhms (though the whole fact that they use opposite directions for current and voltage makes it a bit harder to read than it should be). But I just really like seeing those equations. I think dV/dt = I/C is really quite nice, and while not quite as succinct Vm = Vcmd - (Vm/Rm + C dVm/dt) * Rs is pretty cool too. From r_s_norman from comcast.net Tue Apr 7 21:01:36 2009 From: r_s_norman from comcast.net (r norman) Date: Wed Apr 8 08:48:58 2009 Subject: [Neuroscience] Re: Equation that explains the behaviour of a circuit in voltage clamp References: <6ejgt4pbmdocul789er1f4n7dhc2jdl1lr@4ax.com> <6da09df4-3e9b-45a4-ba88-bb25c9e6e2d9@k19g2000prh.googlegroups.com> <6b1d01f3-49f1-4873-87e4-fc082c948e62@c9g2000yqm.googlegroups.com> Message-ID: <371ot4drfll99m50jvllvsp9bu87henr98@4ax.com> On Tue, 7 Apr 2009 18:50:31 -0700 (PDT), "Bill.Connelly" wrote: >On Apr 6, 6:13?pm, r norman wrote: > >> Are you actually attempting to do voltage clamp experiments or are you >> trying to solve homework problems? > >More general curiosity than anything. What I was REALLY trying to do >was understand the behaviour of the op amp circuitry of your basic >headstage, i.e. the current to voltage converter and then the >differential amp that subtracts Vcmd. I thought I needed to know the >equation for the feedback current, but I didn't. I was trying to prove >to myself that even with a significant series resistance, the op amp >circuitry still behaved properly (even if it doesn't clamp the cell >properly). > >I've gotten quite obsessive about trying to understand every detail >about e-phys recently. I was at a neuroscience course, where a lot of >the other students (some of whom were post docs and had far 'fancier' >papers than I do, doing whole-cell voltage clamp) really had no idea >about what they were actually doing during voltage clamp. They just >kinda assumed that the entire cell was clamped exactly where they set >the dial on the preamp, and the reported current was exactly equal to >the transmembrane current. > >It just kinda reminded me of how anyone can be taught to use a >calculator, and 9 times out of 10, they'll get the right answer, but >if they don't understand math, that 10th time, when they times 2 by 2, >and they get 46873, they wont think it is odd. > >It was really quite interesting looking back on Hodgkin and Huxley's >papers, when they 'invented' series resistance compensation... and the >resistance they were compensating for was only a couple of kiloOhms >(though the whole fact that they use opposite directions for current >and voltage makes it a bit harder to read than it should be). > >But I just really like seeing those equations. I think dV/dt = I/C is >really quite nice, and while not quite as succinct Vm = Vcmd - (Vm/Rm >+ C dVm/dt) * Rs is pretty cool too. You are right in thinking that too many biologists don't understand their equipment and how it works and the many, many potential pitfalls in blindly assumping that the numbers they get are real. On the other hand, there is the story I related of KC Cole, who worried about whether the data was rea,l and Hodking/Huxley, who interpreted the data. Only one of these two groups walked off with the prize. You can go overboard on the fine details. From zhangw from stanford.edu Thu Apr 9 14:34:04 2009 From: zhangw from stanford.edu (Wei Zhang) Date: Thu Apr 9 15:55:35 2009 Subject: [Neuroscience] Anybody experienced with patching on tiny neurons? Message-ID: Hi, I am trying to record from tiny cells and urgently need to ask some technical questions. If you are experienced with tiny neurons (3-5 micro meter) and willing to help, I'd like to invite you for a cup of coffee to talk about it. Thanks. Wei From connelly.bill from gmail.com Tue Apr 14 21:02:11 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Tue Apr 14 21:50:36 2009 Subject: [Neuroscience] Re: Anybody experienced with patching on tiny neurons? References: Message-ID: <2328a4b2-f9fc-4ca0-b7ca-9883391c11d8@y34g2000prb.googlegroups.com> I haven't patched a soma quite that small before (what is it?). Cerebellar granule cells aren't much bigger, and I've patched them before. Is it in a slice, or in a culture dish? And Layer V pyramidal cell dendrites are that size too, and I've hit them. My thoughts are: Use thick walled glass: more glass at the tip has got to make a physically more stable seal, right? Use high resistance electodes: chances are your cells will be high resistance and low capacitance, so you should still get good voltage clamp even with an uncompensated series resistance in the 20-40MOhm range. (and if you're not doing voltage clamp then no problem). On that note, for whatever reason, I have always found that in small cells, say your open tip resistance is 5MOhm, then your whole-cell series resistance will be at least 3x that, i.e. 15MOhm. With big cells I usually find it only goes up by a couple of MOhms. If you're tiny cells are anything like granule cells, and are still in the slice, they will move around alot when you move your pipette up, so once you're near your cell of choice, drop the positive pressure down to low mouth pressure. and if possible approach from the side, rather than from straigh down, as it is easier to tell when you are just touching the cell (so it doesn't spring out of the way). I don't know if those are any of the problems you are having, but seeing as it was "urgent" I thought I'd try On Apr 10, 7:34?am, "Wei Zhang" wrote: > Hi, > ?I am trying to record from tiny cells and urgently need to ask some > technical questions. If you are experienced with tiny neurons (3-5 micro > meter) and willing to help, I'd like to invite you for a cup of coffee to > talk about it. Thanks. > Wei From sibylle.guggenmoos from uniklinik-freiburg.de Mon Apr 20 03:30:52 2009 From: sibylle.guggenmoos from uniklinik-freiburg.de (Sibylle Guggenmoos-Schreyer) Date: Mon Apr 20 09:29:47 2009 Subject: [Neuroscience] problems with dissociated cells & Ca2+ current recording Message-ID: <20090420103052.l9ldpsoi680g4ksw@webmail2.uniklinik-freiburg.de> I am trying to record Ca2+ currents (whole-cell) from acutely dissociated hippocampal CA1 neurons (7-10 day-old rats and mice). However, the cells only survive a couple of minutes after having established the patch. I wonder if this is a dissociating or a bath solution problem, as I can't bubble the bath solution with carbogene (it becomes too acidic). I tried recording Ca currents in acute slices of very young rats before, and those currents were stable but very difficult to influence with various substances which is why I think the bath solution might be the cause of trouble. So, if anyone's got either a good bath solution recipe or a dissociating method or any other idea - I'd be so grateful! Sibylle From connelly.bill from gmail.com Mon Apr 20 16:27:16 2009 From: connelly.bill from gmail.com (Bill.Connelly) Date: Mon Apr 20 19:19:24 2009 Subject: [Neuroscience] Re: problems with dissociated cells & Ca2+ current recording References: Message-ID: <1e102286-e108-4935-8450-adfab715e787@q33g2000pra.googlegroups.com> Hi Sibylle, What is happening that is making you say that the cells aren't surviving? Are you just loosing the seal? You would assume that if the cells were dying because of some problem with your solutions, they would be dead long before you put a patch electrode on them. I suppose my first suggestion is to try a different dissociation techneque. There are a large number of them out there, from the Bill Catterall school who use Na Isethionate for the dissociation and bubble with pure oxygen (140 Na isethionate, 2 KCl, 4 MgCl2, 0.1 CaCl2, 23 glucose, 15 HEPES, pH 7.4 bubbled with 100% O2), to just a straight bicarbonate based aCSF with protease. My other thought is maybe forget about dissociated cells. Try nucleated patches. They're a lot easier than most people make it sound. Especially from such young tissue. You can pull the nucleated sphere out above the level of the slice, so you get excellent drug access. You'll have a 10-15MOhm series resistance over a 500M-1GOhm membrane, with 10pF capacitance, so you'll get excellent voltage clamp. On Apr 20, 8:30?pm, Sibylle Guggenmoos-Schreyer wrote: > I am trying to record Ca2+ currents (whole-cell) from acutely ? > dissociated hippocampal CA1 neurons (7-10 day-old rats and mice). ? > However, the cells only survive a couple of minutes after having ? > established the patch. I wonder if this is a dissociating or a bath ? > solution problem, as I can't bubble the bath solution with carbogene ? > (it becomes too acidic). I tried recording Ca currents in acute slices ? > of very young rats before, and those currents were stable but very ? > difficult to influence with various substances which is why I think ? > the bath solution might be the cause of trouble. > So, if anyone's got either a good bath solution recipe or a ? > dissociating method or any other idea - I'd be so grateful! > Sibylle From t.lewis from unsw.edu.au Mon Apr 20 18:47:00 2009 From: t.lewis from unsw.edu.au (Trevor Lewis) Date: Mon Apr 20 19:19:36 2009 Subject: [Neuroscience] Re-crystallising dextran rhodamine Message-ID: <49ED0974.2040503@unsw.edu.au> Does anyone out there have experience re-crystallising dextran rhodamine? I have been given some dextran rhodamine where the crystals have all sort of 'melted' together (from poor storage) and so needs to be dissolved and recrystallised. I expect it is probably straight forward, but I haven't done it before so thought I would ask for any tips / tricks. Thanks, Trevor From rkmishra from cbcs.ac.in Wed Apr 22 05:18:54 2009 From: rkmishra from cbcs.ac.in (Ramesh Mishra) Date: Wed Apr 22 07:49:12 2009 Subject: [Neuroscience] Call for papers: IJMBC Message-ID: <939e39190904220318l27a3933ah4f4802e6ced2c791@mail.gmail.com> *CALL FOR PAPERS* * * * * *International Journal of Mind, Brain and Cognition** (IJMBC)* * * Manuscripts are invited for the first issue of IJMBC to be published in 200= 9 in various areas of cognitive science and allied disciplines. The journal i= s an international peer reviewed journal and initially will have two issues per year. Articles will include all major areas of cognitive science i.e. Cognitive Science, Cognitive psychology, Neuroscience, Linguistics, Neuropsychology, AI, Computer science, Philosophy and Anthropology etc. as far as they are concerned with theoretical or experimental explorations on all aspects of mind-brain-cognition. The journal will accept both empirical as well as theoretical papers on any aspect of human or machine cognition and will be open to new ideas. *International Journal of Mind, Brain, and Cognitive Science *is a biyearly journal for the multidisciplinary study of minds and other intelligent systems. It publishes articles on cognition from perspectives in artificial intelligence, education, linguistics, neuroscience, philosophy, psychology, and anthropology. Editorial decisions are made on the basis of content, rather than discipline or author, and papers in all areas of cognitive science are welcome. Research reports, which are specifically written for a multidisciplinary audience, are given the highest priority Merely confirmatory research will be given less importance. The journal is edited by Prof. Probal Dasgupta and has an international panel of associated editors. *Types of articles* The following kinds of articles are appropriate for the journal: (a) theories or theoretical analyses of cognitive processes and brain theory; (b) experimental studies relevant to theoretical issues in cognitive science; (c) computational models of neural and cognitive processes and (d) discussions of new problem areas or methodological issues in cognitive science. The journal will publish four categories of articles. Regular articles have a word limit of 10000 words. Brief reports have a target length of about 4,000 words. Letters to the editor will typically consist o= f approximately 1,000 words, and will be commentaries on articles, responses to commentaries, and discussion items of general relevance to the cognitive science community. Book reviews will typically be around 1000 words. *Editor in Chief* Probal Dasgupta (ISI Kolkotta) * * *Associated Editors* Surumpudi Bapi Raju (University of Hyderabad) Rajesh Kasturirangan (Indian Institute of Science, Bangalore) Thomas Lachmann (University of Kiserslaten, Germany) Ramesh Kr Mishra (CBCS, Allahabad University) Lynn Nadel (University of Arizona) Ralph Radach (University of Florida) Anindya Sinha (National Institute of Advanced Studies, Bangalore) Narayanan Srinivasan (CBCS, Allahabad University) Ulrich Ettinger (Institute of Psychiatry, King=92s College London) Peter Lane (University of Hertfordshire) All articles will be internationally peer reviewed. Articles should be sent to the Editor in Chief. The Editor-in-Chief will send the article to the appropriate Associate Editor. *Manuscript Submission:* Authors should send the papers as an email attachment to the Editor-in-Chief. Authors may send queries concerning the submission process, manuscript status, or journal procedures to the editorial office or the concerned associate editor. Manuscripts should conform to APA 5th edition as specified in the *Publicat= ion Manual of the American Psychological Association *with the exceptions and considerations listed below. Authors may be asked to re-format manuscripts that do not conform to the following guidelines prior to editorial evaluation Articles may be submitted to Prof. Probal Dasgupta, Editor in Chief on his e-mail by July 31st 2009 Prof. Probal Dasgupta Professor of Linguistics Indian Statistical Institute Kolkotta, India E-mail: probal53@yahoo.com Journal Website : http://www.bahripublications.com/ijmbc/language_forum.htm --=20 Ramesh Kumar Mishra PhD Centre for Behavioural and Cognitive Science ( CBCS) University of Allahabad Allahabad 211002 India Email:rkmishra@cbcs.ac.in Ph-91-0532-2460738 ( work) Mob-91-9451872007 Fax-91-0532-2460738( work) http://www.cbcs.ac.in/~rkmishra.htm From sibylle.guggenmoos from uniklinik-freiburg.de Wed Apr 22 16:56:10 2009 From: sibylle.guggenmoos from uniklinik-freiburg.de (Sibylle Guggenmoos-Schreyer) Date: Wed Apr 22 17:07:22 2009 Subject: [Neuroscience] Ca2+ current recording in slices? Message-ID: <20090422235610.nh7pz4phc080ckkw@webmail2.uniklinik-freiburg.de> hey there, thanks a lot for your quick replies and possible solutions! I am probably going to try the Catterall dissociation technique, but as I am under some time pressure it would be better if I could solve my problem with Ca2+ current recording in the acute hippocampal slices. Has anyone experienced that in slices, Ca2+ currents are insensitive to channel blockers, e.g. conotoxin? Currents show an initial rundown but after that, a stable baseline normally persists. I have ruled out an application error, and Na+ and K+ currents are sufficiently blocked. Series resistance doesn't increase a lot during the experiments. Again, I'd be delighted if someone had a possible explanation! Sibylle