Abstract:
A method and a device are disclosed for an electronic neuron emulator for representing both passive and active electrical properties of a live neuron. The currents used to generate action potentials are derived from a pre-charged capacitor. The present invention provides for a more physiological state for testing neuroscience instruments such as the single-electrode voltage clamp and the patch clamp. The device can also include multiple pre-charged capacitors to represent ionic channels with more accurate physiologically parameters.

Description:
BACKGROUND OF THE INVENTION 
     The standard device for testing electronic neuroscience instruments such as a voltage clamp amplifier is a simple resistor-capacitor (RC) circuit. While the RC circuit can represent the passive electrical properties of a live neuron, it cannot generate action potentials to interact with the voltage clamp amplifier in a dynamic way. 
     Previously, Breau et al developed a neuron emulator that used an oscillator to generate the action potentials. The oscillator was a time-varying voltage source, which was too strong to overcome by use of a voltage clamp amplifier. Therefore, it was not possible to voltage-clamp the action potentials generated by this device. 
     The neuron emulator in the present invention uses a novel concept, whereby an action potential is generated by switching a pre-charged capacitor into the output circuitry. Once the capacitor is discharged, it is switched out of the output circuitry and charged up for the next firing of the action potential. The present invention overcame the previous limitations of the neuron emulator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The following description may be further understood with reference to the accompanying drawing in which: 
         FIG. 1  shows an illustrative diagrammatic view of the neuron emulator with which techniques of the invention may be employed. 
         FIG. 2  shows an illustration of resting potential and action potential of the neuron emulator. 
         FIG. 3  shows two RC circuits in parallel to generate the action potential. 
         FIG. 4  shows the switching signal, the computer-simulated action potential and the resultant action potential generated by the neuron emulator. 
         FIG. 5  shows a step clamp experiment with the neuron emulator. 
         FIG. 6  shows an annotated screen shot of an oscilloscope during a voltage clamp experiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses an electronic neuron emulator for a single-electrode setting that is capable of having passive properties (membrane resistance and capacitance) and the active properties (action potential) of a live neuron. A novel design feature of this invention is that the currents used to generate action potentials come from a pre-charged capacitor. Unlike a voltage source or a current source, the charge on the capacitor is limited, thereby providing a more realistic physiological condition for testing existing neuroscience instruments such as the single-electrode voltage clamp and the patch clamp. 
       FIG. 1  shows the circuit diagram of the neuron emulator in  1 . A patch clamp setting  3  shows the circuit that it emulates. The switching signals and the resulting action potential output of the neuron emulator are represented in  4 . The passive properties of the neuron are represented by the circuit of R m  in parallel with C m , R m -C m  circuit  11 . The R m -C m  circuit  11  is connected to a voltage reference representing the resting membrane potential V rest    14 . The active properties of the neuron are represented by the circuit of R ap  in parallel with C ap , R ap -C ap  circuit  12 . The active properties circuit is intermittently connected to V peak    13  for pre-charging. 
     To activate an action potential, the R ap -C ap  circuit  12  undergoes switching in series with the R m -C m  circuit  11 . After discharging, the R ap -C ap  circuit  12  switches out and the R m -C m  circuit  11  connects to the resting membrane potential V rest    14 . The switching operation employs three switches, S1  15 , S2  16 , and S3  17 . All three switches are controlled by a microprocessor  18 . The output of the R m -C m  circuit  11  is sent to the analog-to-digital converter  20  via an amplifier  19 . The microprocessor  18  constantly monitors the membrane potential and adjusts the firing rate accordingly. The output of the R m -C m  circuit  11  represents the membrane potential of the neuron. The output of the R m -C m  circuit  11  is accessed externally via resistor R a    21  as the output voltage V out    22 , where R a    21  represents the resistance of the electrode. The timing of the switching signals ( 4 ) is done is such as way that the action potential is generated by turning S1 and S2 off and S3 on. The timing of the switching signals  4  generates the action potential by turning S1  15  and S2  16  off and turning S3  17  on. 
       FIG. 2  further describes the switching of the R ap -C ap  circuit  12  in two positions, Stage 1 and Stage 2. Stage 1 represents the resting potential where S1  15  and S2  16  are turned on and S3  17  turned off. In Stage 1, the R ap -C ap  circuit  12  is disconnected from the R m -C m  circuit  11  and is charged by V peak    13 . Stage 2 represents the action potential where S1  15  and S2  16  turned off and S3  17  turned on. In the Stage 2, the R ap -C ap  circuit  12  is connected in series with the R m -C m  circuit  11 . The output V out    22  momentarily jumps to V peak    13  and then discharges. The firing of consecutive action potentials is accomplished by alternating between Stage 1 and Stage 2. 
     Surprisingly, the aforementioned neuron emulator produces an action potential that has the waveform of a simple exponential discharge. The waveform is further improved to be more representative of a real action potential than previously. 
       FIG. 3  shows another embodiment of the present invention using two RC circuits in parallel to generate the action potential. Furthermore, the circuit elements are adjusted to physiological states of relevance. In the disclosed embodiment, the example represents the squid giant axon with physiological parameters  53  described by Hodge and Huxley. In this embodiment, the R Na -C Na  circuit  51  represents the sodium channel and the R K -C K  circuit  52  represents the potassium channel. Any other physiological variation or state is possible by tuning the circuit parameters, adding additional R-C circuits, or a combination of both to represent different ionic channels for the generation of action potentials. 
     EXAMPLE 1 
     Demonstration of Neuron Emulator Device 
     The neuron emulator was constructed using a single R-C circuit as described above.  FIG. 4  shows the results of a study where the functionality of the neuron emulator is demonstrated. In the demonstration, the switching signal, the computer-simulated action potential and the resultant action potential generated by the neuron emulator device are shown. Remarkably, the action potential was uniformed reproduced by the device in several switching. 
       FIG. 5  shows the result of a step clamp experiment with the neuron emulator. The firing rate of the action potential was increased as the membrane potential was raised by the externally injected current. 
       FIG. 6  is an annotated screen shot of an oscilloscope during a voltage clamp experiment. A commercial voltage clamp amplifier was connected to the neuron emulator and successfully implemented a voltage clamp. An action potential was generated at each on-set of the switching signal shown on channel 3 (CH3). The output voltage was successfully clamped to a constant voltage as shown on channel 2 (CH2). The feedback current responsible for canceling out the action potential was shown on channel 1 (CH1). 
     Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the inventions.