Method and apparatus for measurement of neural response

1. A device for measuring a neural response evoked by a neural stimulus, the device comprising:

at least a first sense electrode and a second sense electrode, the first and second sense electrodes being configured to be positioned at distinct locations along a neural pathway;

a first measurement amplifier circuit configured to amplify signals from the first sense electrode;

a second measurement amplifier circuit configured to amplify signals from the second sense electrode; and

a control unit configured to apply the neural stimulus, the control unit further configured to make a first recording of a first compound action potential evoked by the neural stimulus, the first recording being made using the first measurement amplifier circuit and the first sense electrode, the control unit further configured to make, simultaneously with the first recording, a second recording of the first compound action potential evoked by the stimulus, the second recording being made using the second measurement amplifier circuit and the second sense electrode;

wherein the first measurement amplifier circuit has a first transfer function and the second measurement amplifier circuit has a second transfer function, and wherein the second transfer function differs from the first transfer function in a manner corresponding to a variation in the first compound action potential as the first compound action potential travels between the first sense electrode and the second sense electrode.

2. The device of claim 1 , wherein a gain of the first transfer function of the first measurement amplifier circuit is different to a gain of the second transfer function of the second measurement amplifier circuit, in a manner which compensates for a drop in amplitude of the first compound action potential as the first compound action potential travels between the first sense electrode and the second sense electrode.

3. The device of claim 1 wherein at least one of the first measurement amplifier circuit and the second measurement amplifier circuit further comprises a matched filter matched to a response and which compensates for dispersion and spectral variation in the first compound action potential as the first compound action potential travels between the first sense electrode and the second sense electrode.

4. The device of claim 2 , wherein at least one of the first measurement amplifier circuit and the second measurement amplifier circuit further comprises a matched filter which compensates for dispersion and spectral variation in the first compound action potential as the first compound action potential travels between the first sense electrode and the second sense electrode.

5. The device of claim 1 , where the first and second electrode are a distance d apart and a selected neural fibre class has a conduction velocity of c, and wherein the control unit is further configured to delay the first recording by a time period t=d/c to produce a delayed first recording and wherein the control unit is further configured to compare the delayed first recording with the second recording.

6. The device of claim 1 , wherein the control unit is configured to sum together the first recording and the second recording.

7. The device of claim 1 , wherein the control unit is further configured to obtain more than two recordings from respective electrodes spaced apart along the neural pathway.

8. The device of claim 1 , wherein the control unit is further configured to apply phase terms to each of the first recording and the second recording, to compensate for dispersion of the first compound action potential along the neural pathway.