Method and device for detecting a neural response in neural measurements

1. A method for detecting locally evoked neural responses in neural measurements obtained in the presence of noise, the method comprising:

obtaining a first neural measurement of a neural response from a first sense electrode;

obtaining a contemporaneous second neural measurement of the neural response from a second sense electrode spaced apart from the first electrode along a neural pathway of the neural response;

determining a neural response decay, being a measure of a decay in the neural response from the first sense electrode to the second sense electrode;

calculating a ratio of the neural response decay to an amplitude normalising term;

determining from the ratio whether a locally evoked neural response is present in the neural measurement; and

applying neurostimulation in response to presence of the locally evoked neural response using a closed loop feedback circuit.

2. The method of claim 1 wherein the determined presence of the locally evoked neural response is used to characterize the performance of a local electrical stimulus regime.

3. The method of claim 1 wherein the neural response decay is determined by determining a first amplitude of the first neural measurement, determining a second amplitude of the second neural measurement, and calculating a difference between the first amplitude and the second amplitude.

4. The method of claim 1 wherein the neural response decay is determined by determining a first width of the first neural measurement, determining a second width of the second neural measurement, and calculating a difference between the first width and second width.

5. The method of claim 1 wherein the ratio is determined as being a ratio of the amplitude or strength of the first neural measurement to the amplitude or strength of the second neural measurement.

6. The method of claim 3 wherein the amplitude normalising term comprises a sum of scalar variants of the first amplitude and second amplitude.

7. The method of claim 3 wherein the first amplitude is determined at a first moment of the respective first measurement corresponding to an expected occurrence of the neural response determined by reference to an electrical stimulus timing and a distance from a stimulus site of the electrical stimulus to the first sense electrode, and wherein the second amplitude is determined at a second moment of the respective second measurement corresponding to an expected occurrence of the neural response determined by reference to an electrical stimulus timing and a distance from the stimulus site of the electrical stimulus to the second sense electrode.

8. The method of claim 1 wherein the method is repeated in order to obtain a plurality of ratios resulting from repeated application of a given stimulus in order to give a probabilistic indication of the neural response decay to improve the determination of whether a locally evoked response is present.

9. The method of claim 1 wherein the method is performed repeatedly in order to monitor changes in the ratio which occur over time.

10. The method of claim 1 further comprising a step of using a signal quality indicator to detect whether any neural activity is present to avoid false positives.

11. The method of claim 1 further comprising obtaining a contemporaneous third or additional neural measurement from a third or additional sense electrode(s) spaced apart from the first and second electrodes along a neural pathway of the neural response.

12. An implantable device for detecting locally evoked neural responses in neural measurements obtained in the presence of noise, the device comprising:

measurement circuitry for obtaining a first neural measurement of a neural response from a first sense electrode, and for contemporaneously obtaining a second neural response measurement of the neural response from a second sense electrode spaced apart from the first electrode along a neural pathway of the neural response;

a processor configured to determine a neural response decay, being a measure of decay in the neural response from the first sense electrode to the second sense electrode; the processor further configured to calculate a ratio of the neural response decay to an amplitude normalising term; and the processor further configured to determine from the ratio whether a locally evoked neural response is present in the neural measurement; and

a closed loop feedback circuit configured to apply neurostimulation in response to the presence of the locally evoked neural response.

13. A non-transitory computer readable medium for detecting locally evoked neural responses in neural measurements obtained in the presence of noise, comprising instructions which, when executed by one or more processors, causes performance of the following:

obtaining a first neural measurement of a neural response from a first sense electrode;

obtaining a contemporaneous second neural measurement of the neural response from a second sense electrode spaced apart from the first electrode along a neural pathway of the neural response;

determining a neural response decay, being a measure of decay in the neural response from the first sense electrode to the second sense electrode;

calculating a ratio of the neural response decay to an amplitude normalising term; and

determining from the ratio whether a locally evoked neural response is present in the neural measurement;

applying neurostimulation in response to presence of the locally evoked neural response using a closed loop feedback circuit.

14. The implantable device of claim 12 , wherein the processor is configured to determine the neural response decay by determining a first amplitude of the first neural measurement, determining a second amplitude of the second neural measurement, and calculating a difference between the first amplitude and the second amplitude.

15. The implantable device of claim 14 , wherein the processor is configured to calculate the amplitude normalising term as a sum of scalar variants of the first amplitude and second amplitude.

16. The implantable device of claim 12 , wherein the processor is configured to determine the neural response decay by determining a first width of the first neural measurement, determining a second width of the second neural measurement, and calculating a difference between the first width and second width.

17. The implantable device of claim 12 , wherein the processor is configured to determine the ratio as being a ratio of the amplitude or strength of the first neural measurement to the amplitude or strength of the second neural measurement.

18. The implantable device of claim 12 , wherein the processor is configured to determine the first amplitude at a first moment of the first measurement corresponding to an expected occurrence of the neural response to be detected, as determined by reference to an electrical stimulus timing and a distance from a stimulus site of the electrical stimulus to the first sense electrode, and wherein the processor is configured to determine the second amplitude at a second moment of the respective second measurement corresponding to an expected occurrence of the neural response determined by reference to an electrical stimulus timing and a distance from the stimulus site of the electrical stimulus to the second sense electrode.

19. The implantable device of claim 12 , wherein the processor is configured to repeatedly detect whether a locally evoked neural response is present in the neural measurement, in order to obtain a plurality of ratios resulting from repeated application of a given stimulus in order to give a probabilistic indication of the neural response decay to improve the determination of whether a locally evoked response is present.

20. The implantable device of claim 12 , further comprising a signal quality indicator to detect whether any neural activity is present to avoid false positives.