Neural stimulation for reduced artefact

1. A method of evoking and detecting a neural response, the method comprising:

applying a stimulus to evoke a neural response, the stimulus comprising at least three stimulus components, each stimulus component comprising at least one of a temporal stimulus phase and a spatial stimulus pole, wherein a first stimulus component delivers a first charge which is unequal to a third charge delivered by a third stimulus component, the first charge and third charge being selected so as to give rise to reduced artefact at recording electrodes;

using the recording electrodes to obtain a recording of the neural response; and

detecting the neural response in the recording with a vector detector;

wherein a correlation delay of the vector detector, and the first charge and third charge of the stimulus, have values which cause a produced artefact vector to be non-parallel to an evoked neural response vector.

2. The method of claim 1 wherein the inequality between the first charge and third charge causes the artefact vector to be substantially orthogonal to the evoked neural response vector.

3. The method of claim 1 further comprising adaptively adjusting a stimulus duty ratio and/or the correlation delay in order to seek out a zero in a contribution of artefact to the recording of the neural response.

4. The method of claim 1 wherein the stimulus components comprise stimulus phases.

5. The method of claim 4 wherein the magnitude of the first charge is between 0.6 and 0.9 times the magnitude of a second charge delivered by a second stimulus component.

6. The method of claim 5 wherein the magnitude of the first charge is 0.75 times the magnitude of the second charge.

7. The method of claim 1 wherein the vector detector utilises a multi-lobed matched filter template.

8. The method of claim 7 further comprising adjusting a delay τ in the vector detector so as to desirably align the evoked neural response vector.

9. The method of claim 1 wherein the at least three stimulus components comprise spatial stimulus poles of a tripolar stimulus delivered by at least three stimulus electrodes.

10. An implantable device for delivering a neural stimulus, the device comprising:

an array of electrodes comprising at least one nominal stimulus electrode and at least one nominal recording electrode; and

a processor configured to cause the at least one nominal stimulus electrode to apply a stimulus to evoke a neural response, the stimulus comprising at least three stimulus components, each stimulus component comprising at least one of a temporal stimulus phase and a spatial stimulus pole, wherein a first stimulus component delivers a first charge which is unequal to a third charge delivered by a third stimulus component, the first charge and third charge being selected so as to give rise to reduced artefact at recording electrodes, the processor further configured to cause the at least one nominal recording electrode to obtain a recording of the neural response, the processor further configured to detect the neural response in the recording with a vector detector;

wherein a correlation delay of the vector detector, and the first charge and third charge of the stimulus, have values which cause a produced artefact vector to be non-parallel to an evoked neural response vector.

11. The implantable device of claim 10 wherein the inequality between the first charge and third charge causes the artefact vector to be substantially orthogonal to the evoked neural response vector.

12. The implantable device of claim 10 wherein the processor is further configured to adaptively adjust a stimulus duty ratio and/or the correlation delay in order to seek out a zero in a contribution of artefact to the recording of the neural response.

13. The implantable device of claim 10 wherein the stimulus components comprise stimulus phases.

14. The implantable device of claim 13 wherein the magnitude of the first charge is between 0.6 and 0.9 times the magnitude of a second charge delivered by a second stimulus component.

15. The implantable device of claim 14 wherein the magnitude of the first charge is 0.75 times the magnitude of the second charge.

16. The implantable device of claim 10 wherein the vector detector utilises a multi-lobed matched filter template.

17. The implantable device of claim 16 wherein the processor is further configured to adjust a delay τ in the vector detector so as to desirably align the evoked neural response vector.

18. The implantable device of claim 10 wherein the at least three stimulus components comprise spatial stimulus poles of a tripolar stimulus delivered by at least three stimulus electrodes.

19. A non-transitory computer readable medium for delivering a neural stimulus, comprising instructions which, when executed by one or more processors, causes performance of the following:

applying a stimulus to evoke a neural response, the stimulus comprising at least three stimulus components, each stimulus component comprising at least one of a temporal stimulus phase and a spatial stimulus pole, wherein a first stimulus component delivers a first charge which is unequal to a third charge delivered by a third stimulus component, the first charge and third charge being selected so as to give rise to reduced artefact at recording electrodes;

using the recording electrodes to obtain a recording of the neural response; and

detecting the neural response in the recording with a vector detector;

wherein a correlation delay of the vector detector, and the first charge and third charge of the stimulus, have values which cause a produced artefact vector to be non-parallel to an evoked neural response vector.