Can anyone recommend a good book on electric circuits for neurophysiology?
I have seen circuits called "voltage clamps" and "current clamps" that I would like to understand in more detail.
I have a strong background in general intrumentation, and I'd like some material that deals with the particular issues involved in making neuronal recordings in vivo. Specifically, I need to design a circuit that can be used interchangeably for both micro-stimulation AND recording of neuronal activity.
I doubt you will find a book that covers the subject as well as you would want it to. Try looking into scientific journal papers written by doctors who have actually done some similar experiments. If the paper is well written, you can deduce how the equipment was configured. Furthermore in the interest of peer review and repeatability, I'm sure the researcher would discuss the setup directly with you if you asked.
I am guessing that you want to stick a probe into a living creature's brain (I do hope its a worm or fruit fly or something like that) and measure signals and later stimulate similar signals. Ignoring the biological factor, the signals will be in the uV and nA range, pretty small signals to begin with. This is different from an ECG which measures the electric field induced by many neurons working together.
I see the hard part as designing the probe with sufficient shielding so that you do not pick up stray signals from elsewhere in your apparatus. Take a look at the way low noise measurements are made on semiconductor devices.
After that it is just a matter of selecting a signal conditioning amplifier to bring the level up and selecting a data acquisition software and hardware package with enough resolution to record the signal digitally.
I'm sure you can find a signal conditioner for any type of probe (active, passive, differential, etc.). certainly you could try to build a 10000x amplifier but it really is tricky to eliminate noise at the very lowest levels, construction and component selection do count.
To reverse the procedure, play your recorded signal back through an arbitrary waveform generator (an audio card in your PC may work if the signal frequency and sampling rates are appropriate) and through a different amplifier (attenuates back to biological levels) and apply it to the probes. A calibration and verification of waveform procedure is recommended.
Voltage and current clamps are circuits designed to prevent the voltage or the current from exceeding safe limits. There are many different designs depending on the signal level and response time required. Those limits would be low and response time needed would be short so that you would not damage cells from transient noise spikes.
Thanks for your response. You are correct in saying that an electrode is stuck into the creature's brain (in this case a Long-Evans rat, we have IACUC approval). These electrods are small enough (and well sheilded) so that we can actually stick them into individual cells and record the activity of these single cells.
Much research has been done involving the "recording" of neuronal activity. Less has been done with "microstimulation" (ie inducing the neurons to fire by injecting pulses of current). I have done a fairly extensive literature search of articles like these.
The catch here is that we want a circuit that will selectively stimulate or record from the same electrode without having to remove it. Furthermore, we want to have 64 or 128 of these cricuits operating on individual neurons at the same time. We also want to mount the circuit board on the rat's head, and yet it needs to be lightweight enough to not affect the rat's behavior.
I have found very few circuits that have been designed for this kind of function. One promising one that I found in a yet unpublished paper (found on a website) looks like this:
(Assuming the formatting is right) It looks to me like they are using the opamp (with negative feedback and inverting input to GND) to record the neuron's activity. They are able to stimulate the same neuron by turning on the transistor switch with a control signal.
I'd like to find a few more papers like this, but it looks like it hasn't been done much, so I thought I'd take a step back and try to find a book on general circuits/electrophysiology.
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