Apparatus and method for treating neurological disorders
An apparatus for treating neurological disorders comprising at least one electrode implantable in a patient's brain and a processing and stimulation device connected to the at least one electrode. The processing and stimulation device comprises at least one stimulation module adapted to generate a stimulation signal characterised by a plurality of parameters; at least one acquisition module adapted to acquire a signal characteristic of cerebral activity and determine its power in at least one frequency band; and at least one control module of at least one parameter of the stimulation signal as a function of the power of the signal characteristic of cerebral activity acquired, based on a transfer function having a saturating trend, wherein the transfer function is configured to set the at least one parameter of the stimulation signal differently dependent on a plurality of power ranges, by keeping the parameter within a predetermined stimulation range.
1. An apparatus ( 10 ) for treating neurological disorders comprising:
at least one electrode ( 12 ) implantable in the brain of a patient and
a processing and stimulation device ( 14 ) connected to the at least one electrode ( 12 ), wherein the processing and stimulation device ( 14 ) comprises:
at least one stimulation module ( 16 ) adapted to generate a stimulation signal (V stim ) to be sent to the at least one electrode ( 12 ), the stimulation signal (V stim ) being characterised by a plurality of parameters (V a ,V d ,V f ),
at least one acquisition module ( 18 ) of a signal characteristic of cerebral activity coming from the brain of the patient adapted to determine its power (P BF ) in at least one frequency band (BF), and;
at least one control module ( 20 ) of at least one parameter (V a ,V d ,V f ) of the stimulation signal (V stim ) as a function of the power (P BF ) of the signal characteristic of cerebral activity acquired, based on a transfer function having a saturating trend, wherein the transfer function is such as to set said at least one parameter (V a ,V d ,V f ) of the stimulation signal (V stim ) differently dependent on a plurality of power ranges by keeping the at least one parameter (V a ,V d ,V f ) within a predetermined stimulation range ([V i_HighThreshold ;V i_LowThreshold ]) with i =a,d,f, wherein the transfer function with the saturating trend based on a plurality of power ranges is a piecewise function, placing the stimulation parameter equal to a first value (V i2 ) of the stimulation parameter for powers of the signal acquired above a first power limit value and placing the stimulation parameter equal to a second value (V i1 ) of the stimulation parameter for powers of the signal acquired below a second power limit value according to the following law:
sat
(
U
(
P
BF
)
)
=
{
V
i
2
per
P
BF
≥
P
BF
2
U
i
(
P
BF
)
per
P
BF
2
>
P
BF
>
P
BF
1
V
i
1
per
P
BF
≤
P
BF
1
with V i1 and V i2 alternatively set equal to the minimum value V i_LowThreshold and to the maximum value V i_HighThreshold of a stimulation parameter V i , P BF2 and P BF1 equal, respectively, to a maximum limit value and a minimum limit value of the saturation ranges of the stimulation parameter V i and U i (P BF ) being a law of variability of the stimulation parameter V i outside the saturation ranges.
2. The apparatus ( 10 ) for treating neurological disorders according to claim 1 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges is of the following type:
U
i
(
P
BF
)
=
K
1
i
V
i
2
-
V
i
1
P
BF
2
-
P
BF
1
(
P
BF
-
P
BF
1
)
+
V
i
1
.
3. The apparatus ( 10 ) for treating neurological disorders according to claim 2 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges comprises a further additional term (K 2i ), thereby resulting in:
U
i
(
P
BF
)
=
K
1
i
V
i
2
-
V
i
1
P
BF
2
-
P
BF
1
(
P
BF
-
P
BF
1
)
+
V
i
1
+
K
2
i
.
4. The apparatus ( 10 ) for treating neurological disorders according to claim 1 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside of the saturation ranges is of the following type:
U
i
(
P
BF
)
=
K
1
i
(
V
i
2
-
V
i
1
)
*
(
1
1
+
e
-
p
(
P
BF
-
P
BF
2
-
P
BF
1
2
)
)
+
V
i
1
.
5. The apparatus ( 10 ) for treating neurological disorders according to claim 4 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges comprises a further additional term (K 2i ), thereby resulting in:
U
i
(
P
BF
)
=
K
1
i
(
V
i
2
-
V
i
1
)
*
(
1
1
+
e
-
p
(
P
BF
-
P
BF
2
-
P
BF
1
2
)
)
+
V
i
1
+
K
2
i
.
6. The apparatus ( 10 ) for treating neurological disorders according to claim 1 , wherein the at least one acquisition module ( 18 ) comprises a processor for transforming the acquired signal characteristic of cerebral activity in the frequency domain, preferably of the type implementing a Fast Fourier Transform.
7. The apparatus ( 10 ) for treating neurological disorders according to claim 1 , wherein the at least one acquisition module ( 18 ) comprises an integral block and/or a derivative block for signal conditioning of the recorded signal characteristic of cerebral activity.
8. The apparatus ( 10 ) for treating neurological disorders according to claim 1 , wherein the at least one stimulation module ( 16 ) is a pulse generator generating a stimulation signal (V stim ) comprising a pulse train, wherein at least one stimulating parameter (V a ,V d ,V f ) of the plurality of stimulating parameters (V a ,V d ,V f ) characterising the stimulation signal (V stim ) is selected from the group consisting of:
The amplitude of the stimulation pulses;
The stimulation pulse repetition frequency;
The stimulation pulse duration.
9. The apparatus for treating neurological disorders according to claim 1 , wherein the frequency band (BF) is a sub-band of the beta band (10- 35 Hz) or a sub- band of the low frequencies (4-10 Hz).
10. A method ( 100 ) for treating neurological disorders comprising the steps of:
acquiring ( 130 ) at least one signal characteristic of cerebral activity coming from the brain of the patient and determining the power (P BF ) in at least one frequency band (BF); and
adjusting ( 140 ) at least one parameter (V a ,V d ,V f ) of the stimulation signal (V stim ) as a function of the power (P BF ) of the signal characteristic of cerebral activity acquired, based on a transfer function having a saturating trend, wherein the transfer function is such as to set said at least one parameter (V a ,V d ,V f ) of the stimulation signal (V stim ) differently dependent on a plurality of power ranges, by keeping the at least one parameter (V a ,V d ,V f ) within a predetermined stimulation range ([V i_HighThreshold ;V i_LowThreshold ]) with i =a,d,f, wherein the transfer function with the saturating trend based on a plurality of power ranges is a piecewise function, setting the stimulation parameter equal to a first value (V i1 ) of the stimulation parameter for powers of the signal acquired above a first power limit value and setting the stimulation parameter equal to a second value (V i2 ) of the stimulation parameter for powers of the signal acquired below a second power limit value according to the following law:
sat
(
U
(
P
BF
)
)
=
{
V
i
2
per
P
BF
≥
P
BF
2
U
i
(
P
BF
)
per
P
BF
2
>
P
BF
>
P
BF
1
V
i
1
per
P
BF
≤
P
BF
1
with V i1 and V i2 alternatively set respectively equal to the minimum value V i_LowThreshold and to the maximum value V i_HighThreshold of a stimulation parameter V i , P BF2 and P BF1 equal, respectively to a maximum limit value and a minimum limit value of the saturation ranges of the stimulation parameter V i and U i (P BF ) being a law of variability of the stimulation parameter V i outside the saturation ranges.
11. The method ( 100 ) for treating neurological disorders according to claim 10 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges is of the following type:
U
i
(
P
BF
)
=
K
1
i
V
i
2
-
V
i
1
P
BF
2
-
P
BF
1
(
P
BF
-
P
BF
1
)
+
V
i
.
12. The method ( 100 ) for treating neurological disorders according to claim 11 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges comprises a further additional term (K 2i ), thereby resulting in:
U
i
(
P
BF
)
=
K
1
i
V
i
2
-
V
i
1
P
BF
2
-
P
BF
1
(
P
BF
-
P
BF
1
)
+
V
i
1
+
K
2
i
.
13. The method ( 100 ) for treating neurological disorders according to claim 10 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges is of the following type:
U
i
(
P
BF
)
=
K
1
i
(
V
i
2
-
V
i
1
)
*
(
1
1
+
e
-
p
(
P
BF
-
P
BF
2
-
P
BF
1
2
)
)
+
V
i
1
.
14. The method ( 100 ) for treating neurological disorders according to claim 13 , wherein the law of variability (U i (P BF )) of the stimulation parameter (V i ) outside the saturation ranges comprises a further additional term (K 2i ), thereby resulting in:
U
i
(
P
BF
)
=
K
1
i
(
V
i
2
-
V
i
1
)
*
(
1
1
+
e
-
p
(
P
BF
-
P
BF
2
-
P
BF
1
2
)
)
+
V
i
1
+
K
2
i
.
15. The method ( 100 ) for treating neurological disorders according to claim 10 , wherein the stimulation signal (V stim ) comprises a train of pulses and the stimulation parameter (V a ,V d ,V f ) is selected from the group consisting of:
The amplitude of the stimulation pulses;
The stimulation pulse repetition frequency;
The stimulation pulse duration.
16. The method ( 100 ) for treating neurological disorders according to claim 10 , wherein the frequency band (BF) and the parameters of the law of variability are obtained according to the following steps:
a) identifying ( 111 ) at least one maximum threshold value (V i_HighThreshold ) of a stimulation parameter (V i ) beyond which the patient shows signs of actual side effects induced by the stimulation and a minimum threshold value (V i_LowThreshold ) for which the patient shows the minimum or zero benefit induced by stimulation, and setting the extremes of said predetermined stimulation range ([V i2 ;V i1 ]) alternatively and respectively equal to the threshold values (V i_HighThreshold ) and (V i_LowThreshold ) of the stimulation parameter (V i ) or to a percentage thereof;
b) determining ( 112 ) the frequency band (BF), by detecting a frequency peak of the power spectrum of a signal characteristic of cerebral activity of the patient recorded in the absence of stimulation, the frequency band (BF) being centered on such a frequency peak and having a bandwidth selected arbitrarily;
c) recording ( 113 ) the variation over time of the spectral power (P BF ) of a signal characteristic of cerebral activity calculated in the frequency band (BF) in three conditions:
base state;
active stimulation at the maximum threshold stimulation parameter (V i_HighThreshold ) and pharmacological therapy absent; and
active stimulation at the maximum threshold stimulation parameter (V i_HighThreshold ) and pharmacological therapy administered and active;
d) identifying ( 114 ) a maximum spectral power value (P BF2 ) and a minimum spectral power value (P BFI ) of the variation recorded in step c).
17. The method ( 100 ) for treating neurological disorders according to claim 16 , wherein the maximum spectral power value (P BF2 ) of the signal characteristic of cerebral activity calculated in the frequency band (BF) corresponds to a spectral power value (P OFFOFF ) able to be determined when the patient is in the base state and the minimum spectral power value (P BF1 ) corresponds to a spectral power value (P ONON ) able to be determined when the patient undergoes both a pharmacological therapy and an active stimulation therapy at the maximum threshold value (V i_HighThreshold ) of the stimulation parameter.
18. The method ( 100 ) for treating neurological disorders according to claim 17 , wherein the frequency band (BF) is a sub-band of the beta band (10 - 35 Hz).
19. The method ( 100 ) for treating neurological disorders according to claim 18 , wherein the minimum spectral power (P BF1 ) of the signal characteristic of cerebral activity calculated in the frequency band (BF) corresponds to a spectral power value (P OFFOFF ) able to be determined when the patient is in the base state and the maximum spectral power value (P BF2 ) corresponds to the spectral power value (P ONON ) able to be determined when the patient undergoes both a pharmacological therapy and an active stimulation therapy at the maximum threshold value (V i_HighThreshold ) of the stimulation parameter.
20. The method ( 100 ) for treating neurological disorders according to claim 19 , wherein the frequency band (BF) is a sub-band of the low frequencies (4-10 Hz).