Patent Publication Number: US-8543212-B2

Title: Vestibular stimulator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the priority of U.S. application Ser. No. 11/351,388 filed on Feb. 9, 2006 (now U.S. Pat. No. 7,962,217), which is a divisional of U.S. application Ser. No. 10/738,920, filed on Dec. 16, 2003 (now U.S. Pat. No. 7,933,654), which claims the priority of U.S. provisional application No. 60/433,946, filed on Dec. 17, 2002. The contents of the applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF INVENTION 
     This invention relates to treatment for vestibular dysfunction. 
     BACKGROUND 
     When a normal person is stationary, the neurons associated with the vestibular system carry pulse trains that, on average, have a nearly constant pulse-repetition frequency. If the patient changes spatial orientation, the average pulse-repetition frequency of the pulse trains changes. These pulse trains, hereafter referred to as the “vestibular signal”, are transmitted to the brain via the vestibular nerve. On the basis of changes in the average pulse-repetition frequency, the brain determines the patient&#39;s spatial orientation and motion. 
     The vestibular system is not the brain&#39;s only source of information concerning the patient&#39;s spatial orientation. Both the vision and other sensory systems, such as the proprioceptive and tactile systems, provide additional cues. The brain reconciles these additional cues with information from the vestibular system. To the extent that these cues are inconsistent with each other, the patient experiences dizziness. 
     In one afflicted with Meniere&#39;s disease, the vestibular system, for no apparent reason, suddenly begins varying the pulse-repetition frequency of the vestibular signal even when the patient is stationary. This results in severe dizziness. Then, and again for no apparent reason, the vestibular system begins generating a vestibular signal consistent with the person&#39;s spatial orientation, thereby ending the person&#39;s symptoms. 
     Known treatments for Meniere&#39;s disease include surgical removal of the patient&#39;s vestibule. Another treatment involves perfusion of ototoxic drugs that permanently destroy the cilia within the vestibule. As a result, these treatments result in the permanent loss of the patient&#39;s sense of balance. 
     Less draconian treatments for Meniere&#39;s disease include the introduction of drugs having questionable efficacy, acupuncture, and various homeopathic remedies. These treatments have not shown consistent success. 
     SUMMARY 
     In one aspect, the invention includes an apparatus for stimulating the vestibular system. The apparatus includes an actuator disposed to interact with the vestibular nerve and a controller for causing the actuator to interact with the vestibular nerve. The result of the interaction is that the brain receives a stationary signal. 
     Embodiments of the invention include those in which the actuator has an implantable electrode, an antenna, an external electrode, an implantable electrode having a receiver for communication with a transmitter outside the patient, or a magnetic field source, each of which is in communication with the vestibular nerve. Other embodiments include those in which a vibrating element is adapted to mechanically stimulate the vestibule. 
     Other embodiments of the invention include those in which the actuator includes a chemical delivery system adapted for delivering a chemical agent to an active region. Once in the active region, the chemical agent interacts with the vestibular nerve. Such a chemical delivery system might include, for example, a reservoir for containing the chemical agent, and a pump for delivering the chemical agent from the reservoir to the active region. 
     Some embodiments of the apparatus include an externally actuated switch in communication with the controller for enabling external control of an interaction with the vestibular nerve. In other embodiments, the apparatus includes a sensor adapted to detect a first signal on the vestibular nerve. Such a sensor is in communication with the controller for causing the controller to generate a second signal in response to the first signal. 
     In some embodiments, the controller is configured to cause the actuator to generate a signal that, when combined with a non-stationary signal present on the vestibular nerve, causes a stationary signal to be transmitted to the brain. 
     Another aspect of the invention is a method for providing relief from Meniere&#39;s disease by reversibly disabling vestibular function following detection of an attack of Meniere&#39;s disease. 
     In certain practices of the invention, reversibly disabling vestibular function includes temporarily causing the vestibular nerve to carry a stationary signal to the brain. This can be achieved, for example, by causing the vestibular nerve to carry a jamming signal that, when combined with a non-stationary signal present on the vestibular nerve, causes the vestibular nerve to carry a stationary signal to the brain. One example of a jamming signal is a pulse train having a selected pulse repetition frequency. 
     The jamming signal can be generated in a variety of ways, for example by electrical or electromagnetic stimulation of the vestibular nerve, by mechanically stimulating the vestibule, or by exposing the vestibular nerve to a chemical agent. 
     In one practice of the invention, the chemical agent is a neurotransmitter. However, the chemical agent can also be a nerve-impulse blocking agent. 
     In another practice of the invention, the method includes detecting onset of an attack of Meniere&#39;s disease, and applying a jamming signal following detection of an attack. Other practices of the invention include those in which the jamming signal is removed at the end of an attack of Meniere&#39;s disease. 
     Meniere&#39;s disease is episodic in nature. During an attack, the patient experiences severe discomfort. However, between attacks, the patient is largely asymptomatic. Conventional methods of treating Meniere&#39;s disease disable vestibular function permanently, thereby leaving the patient with no vestibular function even during asymptomatic periods. The invention provides relief from the disease by disabling vestibular function only during the attack itself, but not during the period between such attacks. As a result, the patient&#39;s vestibular function is available during asymptomatic periods. 
     Another aspect of the invention is a method for providing relief from hemineglect by isothermally stimulating vestibular function. 
     In certain practices of the invention, stimulating vestibular function includes causing the vestibular nerve to carry a stationary signal to the brain. This can be achieved, for example, by causing the vestibular nerve to carry a jamming signal that, when combined with a non-stationary signal present on the vestibular nerve, causes the vestibular nerve to carry a stationary signal to the brain. One example of a jamming signal is a pulse train having a selected pulse repetition frequency. 
     The jamming signal can be generated in a variety of ways, for example by electrical stimulation of the vestibular nerve, by mechanically stimulating the vestibule, or by exposing the vestibular nerve to a chemical agent. 
     In one practice of the invention, the chemical agent is a neurotransmitter. However, the chemical agent can also be a nerve-impulse blocking agent. 
     These and other features and advantages of the invention will be apparent from the following detailed description and the accompanying figures, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an apparatus according to the invention; 
         FIG. 2  is an embodiment in which the actuator of  FIG. 1  is an electrode; 
         FIG. 3  is a wireless embodiment of the apparatus of  FIG. 2 ; 
         FIG. 4  is an embodiment in which the actuator of  FIG. 1  is an antenna; 
         FIG. 5  is an embodiment having an automatic control unit with a feedback loop; 
         FIG. 6  is an embodiment in which the actuator of  FIG. 1  is a coil for generating a magnetic field; 
         FIG. 7  is an embodiment having an actuator that shakes the vestibule; and 
         FIG. 8  is an embodiment in which an actuator applies chemical agents to the vestibular nerve area. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an apparatus  10  for providing symptomatic relief from Meniere&#39;s disease. The apparatus includes an actuator  12  in communication with the vestibular nerve  14 . A control unit  16  in electrical communication with the actuator  12  provides control over a jamming signal present at the actuator  12 . As used herein, electrical communication encompasses both a wireless connection, in which communication is carried out by electromagnetic waves, and a wired connection. In one particular embodiment disclosed herein, this jamming signal is a pulse train having a controllable pulse amplitude and pulse-repetition frequency, both of which are set by the control unit  16 . However, the jamming signal can also be any other time-varying stimulus. Examples of other jamming signals include sinusoidal signals or any other oscillatory signals. 
     A power source  18 , such as a rechargeable battery, provides power to both the actuator  12  and the control unit  16 . 
     During an attack of Meniere&#39;s disease, a vestibular signal on the vestibular nerve develops time-varying changes in the neural pulse-repetition frequency even when the patient&#39;s spatial orientation is not changing. A time-varying signal of this type, in which the amplitude or frequency is modulated with time, is often referred to as a “non-stationary” signal. 
     The patient interprets a non-stationary signal on the vestibular nerve as indicating a change in his spatial orientation, even when his spatial orientation has not changed at all. The vestibular signal, together with the mismatch between the vestibular signal and other motion cues available to the brain results in dizziness and discomfort. 
     The apparatus  10  relieves the discomfort of Meniere&#39;s disease by temporarily and reversibly disabling vestibular function. It does so by jamming the vestibular signal with the jamming signal. The characteristics of this are selected so that the combination of the jamming signal and the vestibular signal results in a signal having a constant pulse-repetition frequency. Examples of characteristics that can be selected to achieve this are the jamming signal&#39;s pulse amplitude and pulse-repetition frequency. 
     Proper selection of the jamming signal&#39;s characteristics causes the brain to receive a stationary signal instead of the non-stationary signal that characterizes Meniere&#39;s disease. To the extent that the patient remains stationary during the attack, the brain receives a signal consistent with the patient&#39;s constant spatial orientation. Since the brain now receives a signal consistent with other motion cues, the discomfort associated with Meniere&#39;s disease is alleviated. 
     The amplitude of the jamming signal depends in part on the type of actuator  12 . In one embodiment, shown in  FIG. 2 , the actuator  12  includes a jamming electrode  20  that is implanted proximate to the vestibular nerve  14 . In this case, the amplitude is selected such that a current on the order of a milliamp or less is present at the jamming electrode  20 . Communication between the control unit  16  and the jamming electrode  20  can be established by a wire that perforates the skull. However, to avoid the need to perforate the skull, communication between the control unit  16  and jamming electrode  20  can also be wireless. This is achieved by a control unit  16  having a transmitter  21  and an actuator  12  having a receiver  23  in communication with the jamming electrode  20 , as shown in  FIG. 3 . 
     Another embodiment, shown in  FIG. 4 , avoids the need to implant by providing an actuator  12  that includes an antenna or external electrode  22  worn by the patient adjacent to the head. In this case, the amplitude is increased so that the vestibular nerve  14  is illuminated by sufficient power from the actuator  12 . Typically, the amplitude is raised so that a current on the order of at least tens of milliamps is present on the antenna  22 . 
     The jamming signal characteristics are selected such that the resulting combination of the jamming signal and the vestibular signal results in a signal having a constant pulse-repetition frequency. A time-varying signal of this type, the spectrum of which is essentially constant in time, will be referred to herein as a “stationary signal.” In one embodiment, the pulse-repetition frequency is approximately equal to the maximum neuron firing rate, which is typically on the order of 450 Hz. This pulse-repetition frequency is likely to result in the synchronous firing of neurons at or near their maximum firing rate. However, it may be useful in some cases to have a much higher pulse-repetition frequency, for example in the 1-10 kilohertz range, so that neurons fire asynchronously. 
     The jamming signal need only be on during an attack of Meniere&#39;s disease. When the attack subsides, the jamming signal is removed and the patient regains normal vestibular function. The control unit  16  thus provides a mechanism for applying and removing the jamming signal. 
     In one embodiment, the control unit  16  has a patient-accessible switch  24 , as shown in  FIG. 1 . When the patient feels the onset of an attack, he uses the switch to apply the jamming signal. A disadvantage of this type of control unit  16  is that because the jamming signal masks the symptoms of the attack, the patient is unable to tell whether the attack is over. 
     In the embodiment having a patient-accessible switch  24 , the patient can simply use the switch to turn off the jamming signal after a reasonable time has elapsed. The resulting change in the pulse-repetition frequency of the signal received by the brain may result in some dizziness. However, if the attack of Meniere&#39;s disease is in fact over, this dizziness should fade shortly. If the dizziness does not fade, the patient uses the switch  24  to turn the jamming signal on again. 
     Alternatively, the switch  24  can include a timer that automatically turns the jamming signal off after the lapse of a pre-determined jamming interval. In some embodiments, the length of the jamming interval is user-controlled, whereas in others, the length of the jamming interval is hard-wired into the control unit  16 . If the dizziness does not fade after the stimulation has been turned off, the patient uses the switch  24  to turn the jamming signal on again. 
     The control unit  16  can also be an automatic control unit  16  having a feedback loop, as shown in  FIG. 5 . In this case, a sensor electrode  26  is implanted proximate to the vestibular nerve  14  to measure the vestibular signal. When the control unit  16  detects appropriate time-varying changes in the pulse-repetition frequency of the vestibular signal, it causes the control unit  16  to apply the jamming signal to the jamming electrode  20 . In this case, the jamming signal characteristics can be made to vary in response to the characteristics of the measured vestibular signal. 
     The jamming signal need not be an electrical signal. For example, in the embodiment of  FIG. 6 , the jamming signal is generated by a magnetic field generated by a coil  28  located outside the patient. 
     Another embodiment, shown in  FIG. 7 , generates a jamming signal by mechanical stimulation of the vestibule  30 . In this case, a piezoelectric element  32  is implanted proximate to the vestibule  30 . The controller sends a jamming signal to the piezoelectric element  32 , thereby causing the piezoelectric element  32  to flex and relax at a particular frequency. The motion of the piezoelectric element  32  is transmitted to the vestibule  30 , thereby causing portions of the vestibule  30  to vibrate at that frequency. The vibration of the vestibule  30  causes the generation of an additional component of the vestibular signal. This additional component combines with the component resulting from the attack of Meniere&#39;s disease. Again, by proper selection of the pulse-repetition frequency, the signal received by the brain on the vestibular nerve  14  will again have a constant pulse-repetition frequency. 
       FIG. 8  shows an embodiment in which chemical agents interfere with the vestibular signal. In this case, the controller drives a pump  34  that pumps a chemical agent stored in a reservoir  36 . The chemical agent can be a neurotransmitter to be administered to one or more synapses  38  at doses sufficient to drive repeated firing of the neurons at or close to their maximum firing rates. Again, this results in the generation of a jamming signal that interferes with, and effectively masks, the vestibular signal. Alternatively, the reservoir  36  can contain a neurosuppressive agent to be applied to the synapses to prevent the vestibular signal from reaching the brain. In this case, the vestibular signal that reaches the brain has a constant pulse-repetition frequency of zero. 
     The apparatus described herein has therapeutic purposes other than treatment of Meniere&#39;s disease. For example, the apparatus can be used to isothermally stimulate the vestibular system of a stroke victim afflicted with hemineglect. Such stimulation can provide relief from symptoms of hemineglect. 
     The foregoing embodiments of the apparatus all provide temporary and controllably reversible disabling of vestibular function by controllably jamming the vestibular signal with a jamming signal. Other embodiments are within the scope of the following claims: