Feedback Loop Control of Neuromodulation Device

1 . A method of controlling a neural stimulus, the neural stimulus being defined by at least one stimulus intensity parameter, the method comprising:

generating a stimulus intensity parameter to control a stimulator that generates a stimulus current for application to a tissue;

measuring a response of the tissue, evoked by the stimulus current;

determining a forward adjustment parameter as a function of the stimulus intensity parameter;

determining a feedback parameter derived from the measured response and the forward adjustment parameter; and

adjusting the stimulus intensity parameter according to the feedback parameter.

2 . The method of claim 1 , wherein the forward adjustment parameter is non-zero when the stimulus intensity parameter is non-zero.

3 . The method of claim 1 , further comprising providing a target response level, wherein determining a feedback parameter comprises:

adjusting the target response level in accordance with the forward adjustment parameter to produce an adjusted target response level; and

deriving the feedback parameter from a difference between the measured response and the adjusted target response level.

4 . The method of claim 1 , wherein determining a feedback parameter comprises adjusting the measured response according to the forward adjustment parameter to produce an adjusted response.

5 . The method of claim 1 , wherein the function of the stimulus intensity parameter is a forward adjustment function, wherein the forward adjustment function defines a monotonically increasing relationship between the forward adjustment parameter and the stimulus intensity parameter.

6 . The method of claim 1 , further comprising:

determining a change in an impedance level of the tissue; and

adjusting a gradient of the forward adjustment function based on the change the impedance level.

7 . The method of claim 6 , wherein adjusting the gradient of the forward adjustment function comprises:

in response to an increase in the impedance level, reducing the gradient of the forward adjustment function; and

in response to a decrease in the impedance level, increasing the gradient of the forward adjustment function.

8 . The method of claim 4 , wherein the feedback parameter is derived according to the difference between a target stimulus intensity level and the adjusted response.

9 . The method of claim 8 , further comprising determining an adjusted target stimulus intensity level based on the target stimulus intensity level and the forward adjustment function.

10 . The method of claim 9 , further comprising adjusting the forward adjustment function to increase a difference between the adjusted target stimulus intensity level and a comfort stimulus intensity threshold.

11 . The method of claim 1 , further comprising:

determining an artefact compensation component based on an artefact component of the measured response of the tissue; and

adjusting the measured response based on the artefact compensation component.

12 . The method of claim 11 , further comprising determining the artefact component as a function of the stimulus intensity parameter.

13 . The method of claim 11 , wherein adjusting the measured response based on the artefact compensation component comprises adjusting the forward adjustment parameter based on the artefact compensation component.

14 . The method of claim 1 , wherein adjusting the stimulus intensity parameter according to the feedback parameter derived from the measured response comprises:

in response to the measured response being greater than a target value, reducing the stimulus intensity parameter in accordance with a reduction rate; and

in response to the measured response being less than the target value, increasing the stimulus intensity parameter in accordance with a growth rate,

wherein a magnitude of the reduction rate is not equal to a magnitude of the growth rate.

15 . An implantable device for controllably applying a neural stimulus defined by at least one stimulus intensity parameter, the device comprising:

one or more stimulus electrodes to deliver stimulus to a tissue to evoke a compound action potential response of the tissue;

a stimulator for controlling the one or more stimulus electrodes in accordance with the at least one stimulus intensity parameter;

measurement circuitry for measuring the evoked compound action potential response of the tissue; and

a control unit configured to,

generate the stimulus intensity parameter,

measure the response of the tissue, evoked by the stimulus current,

determine a forward adjustment parameter as a function of the stimulus intensity parameter,

determine a feedback parameter derived from the measured response and the forward adjustment parameter, and

adjust the stimulus intensity parameter according to the feedback parameter.

16 - 25 . (canceled)

26 . The device of claim 15 , wherein the control unit is configured to determine the feedback parameter by:

adjusting a target response level in accordance with the forward adjustment parameter to produce an adjusted target response level; and

deriving the feedback parameter from a difference between the measured response and the adjusted target response level.

27 . The device of claim 15 , wherein the control unit is configured to determine the feedback parameter by adjusting the measured response according to the forward adjustment parameter to produce an adjusted response.

28 . The device of claim 15 , wherein the function of the stimulus intensity parameter is a forward adjustment function, wherein the forward adjustment function defines a monotonically increasing relationship between the forward adjustment parameter and the stimulus intensity parameter.

29 . The device of claim 15 , wherein the control unit is further configured to:

determine an artefact compensation component based on an artefact component of the measured response of the tissue; and

adjust the measured response based on the artefact compensation component.

30 . The device of claim 15 , wherein the control unit is configured to adjust the stimulus intensity parameter according to the feedback parameter derived from the measured response by:

in response to the measured response being greater than a target value, reducing the stimulus intensity parameter in accordance with a reduction rate; and

in response to the measured response being less than the target value, increasing the stimulus intensity parameter in accordance with a growth rate,

wherein a magnitude of the reduction rate is not equal to a magnitude of the growth rate.