Abstract:
A head-mountable EEG electrode-containing device is provided based on radially adjustable electrodes to fit the wearer&#39;s unique head size and shape. The head-mountable device with an electrode array positioned therein includes multiple head-mountable device sections that are interconnected by mechanical fasteners to facilitate sizing and positioning of the head-mountable device. An array of resilient sleeves is positioned within each head-mountable device section. Each resilient sleeve houses an individual electrode and is deformable for self-orienting. The deformation of the sleeve is such that a central axis passing through the individual electrode housed within the resilient sleeve is maintained in a position approximately normal to a plane tangential to a scalp portion positioned beneath that electrode.

Description:
FIELD OF THE INVENTION 
     The invention relates to an EEG brain biofeedback device for rehabilitation, training or entertainment and, more particularly, to a brain biofeedback device having self-orienting, radially-adjustable EEG electrodes. 
     BACKGROUND OF THE INVENTION 
     Stroke is a cerebrovascular accident with high disability and mortality rates. One of the main factors affecting the independence of stroke survivors is hand function, which is closely related to daily activities, such as feeding and self-cleaning. Neuro-rehabilitation following a stroke or other cerebrovascular event is a major future challenge as populations age and have increasing longevity. 
     Electroencephalography (EEG) is a technique for measuring bioelectrical signals generated by the cerebral cortex of a brain. The signals are directly related to voluntary motor contributions from the central nervous system (e.g., EEG motor imagery, the thinking and planning of a physical task). EEG signals are more directly related to the voluntary contribution with stronger signals from a patient in the early post-stroke stage. Currently the types of EEG systems that can measure these signals are non-portable, that is, they are sufficiently large as to restrict their use to a research laboratory environment. The measurement system requires a lengthy period to prepare and correctly position all the EEG electrodes. Further, without visual indicators, correct electrode placement is difficult to verify and typically must be performed by skilled technicians. 
     Various devices have been used in an attempt to correctly position and hold EEG electrodes adjacent to a patient&#39;s scalp. For example, caps are used to position the EEG electrodes. Such electrode caps facilitate positioning of EEG electrodes by technicians within a short period of time (e.g., about 5 minutes). Following electrode positioning, conductive gel is injected to reduce the scalp-electrode impedance and thereby record strong EEG signals. 
     However, conventional attempts to position EEG electrodes using various headgear are insufficient because they do not appropriately account for variations among head sizes and shapes in the patient population. Typically, conventional approaches use several specific sizes in order to approximate various head sizes along with elastic materials to roughly elongate a cap to more closely fit different head shapes. However, conventional electrode caps are based on approximating the upper head as having a hemispherical shape. Since the human head does not have a hemispherical shape, an equal elongated head size approximation method causes error in the electrode positioning. 
     Thus there is a need in the art for an improved EEG electrode positioning device, particularly a positioning device that is lightweight with sufficient resilient properties to ensure proper electrode positioning on a variety of head sizes and shapes. There is a further need in the art for visual indication that the electrodes are correctly positioned and that the electrode-scalp impedance is within an acceptable range for EEG signal measurement. Such a device could facilitate a portable brain-training system with minimal set-up time that could be used in clinical and residential settings. 
     SUMMARY OF THE INVENTION 
     The present invention presents a novel head-mountable EEG electrode-containing device based on radially adjustable electrodes to fit the wearer&#39;s unique head size and shape rather than merely laterally elongating the space between electrodes as in conventional electrode caps. 
     A head-mountable device with an electrode array positioned therein includes multiple head-mountable device sections that are interconnected by mechanical fasteners to facilitate sizing and positioning of the head-mountable device. An array of resilient sleeves is positioned within each head-mountable device section. Each resilient sleeve houses an individual electrode and is deformable. The deformation of the sleeve is such that a central axis passing through the individual electrode housed within the resilient sleeve is maintained in a position approximately normal to a plane tangential to a scalp portion positioned beneath that electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a brain training device consisted of EEG headset module in accordance with a preferred embodiment of the present invention as worn. 
         FIG. 2  schematically depicts expansion of a head dimension in a radial direction based on measurements of human populations. 
         FIGS. 3A and 3B  depict top and side views of positioning points for the head-mountable device electrode array of the present invention. 
         FIGS. 4A and 4B  are, respectively, front and side views of the EEG headset module of the device of  FIG. 1 . 
         FIG. 5  is a top view of the EEG headset module of the device of  FIG. 1  indicating the EEG electrode positions which covered the central, frontal and parietal regions of the brain activity based on the EEG electrode location from the International 10/20 system for a 64 channel EEG. 
         FIG. 6  is a cross-sectional view illustrating details of a self-orienting EEG electrode attached inside the headset module of the device of  FIG. 1 . 
         FIGS. 7A and 7B  are cross-sectional views of a self-orienting EEG electrode of  FIG. 6  in contact with the skin surface with a certain distance and angle that the electrode can be placed on the various size and shape of the head.  FIG. 7B  shows the self-orienting properties of the electrode with a central axis passing through the electrode maintained in a position approximately normal to a plane tangential to the portion of the scalp positioned beneath the electrode. 
         FIG. 8  is a front view of the EEG headset module of the device of  FIG. 1  when both left and right segments of the EEG headset module are bent upward for placing the device on the head or removing the device from the head. 
         FIG. 9  is a front view of the EEG headset module of the device of  FIG. 1  when both left and right segments of the EEG headset module are attached on the head surface. 
         FIGS. 10A and 10B  are rear perspective views of the EEG headset module of the device of  FIG. 1  showing both left and right reference electrodes adjusted along the axis when the device is worn. 
         FIG. 11  is the top view of the self-orienting EEG electrode of  FIG. 6  showing a diffused illumination pattern of the light ring for the visual bio-feedback signal. 
         FIG. 12  is a top view of the EEG headset module of the device of  FIG. 1  indicating the diffused illumination color pattern on the visual signal indicator of  FIG. 11  which placed outside of the device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the drawings in detail,  FIG. 2  depicts an extension of a head size in a radial direction obtained by comparing standard head shapes and sizes (see references 1-6) according to the present invention. Using these measurements and extensions, the present invention creates a new design for a head-mountable electrode array device. The device relies on radially adjustable electrodes that fit an individual head size in contrast to conventional elastic caps that laterally elongate the space between the electrodes. 
     Turing to  FIG. 3 , the head-mountable device is attached on the wearer&#39;s head using the precise orientation and position with reference to the nasion and inion, and also the ear auricular points to find the vertex point (Cz), which is the central point between nasion and inion and also the central point between left and right auricular points. The device is also aligned with the central line, which runs along the nasion and inion. 
     Based on the measurements and positions of  FIGS. 2 and 3 ,  FIG. 1  depicts a head-mountable device  181  that can measure bioelectrical signals generated by a cerebral cortex of a brain configured such that individual electrodes are radially adjustable for individual variations in head size and shape. The device of  FIG. 1  is optionally part of a system used for brain training and rehabilitation. 
     Referring to  FIGS. 4 and 5 , the EEG head-mountable device  181  includes EEG electrode positions  30  covering the central, frontal and parietal regions of the skull of the head according to the international 10/20 system. The numeral  30  is used to indicate the overall electrode structure while the bioelectrical signal sensing portion (the actual electrical portion of the electrode) is indicated by reference numeral  32  (see  FIG. 6 ). The numeral  38  is used to indicate the outer shell of the head-mountable device  181 . The head-mountable device  181  comprises central device segment  21 , left device segment  22 , right device segment  23  and auxiliary device segment  24 . The auxiliary segment  24  includes left and right back ear reference electrodes  31   n . Each of the EEG electrodes  30  is affixed to a predetermined electrode position in the EEG head-mountable device. An electrode is placed with spacing of 20% of the nasion-inion distance and 20% of the ear auricular distance for the vertical and horizontal line respectively according to the standard 10/20 system. For a 64-channel EEG, the vertical distance between electrodes is reduced by half and becomes 10% of the nasion-inion distance and the horizontal distance becomes 10% of the ear auricular distance. 
       FIG. 6  is a cross-sectional view of an electrode  30 . The bioelectrical sensing portion  32  is positioned within a resilient electrode sleeve  31 . The resilient electrode sleeve  31  is an integrally-formed structure that includes semicircular damper portion  35 . This configuration allows the resilient sleeve  31  to be compressed within a certain distance to change its orientation to adapt to various head sizes and shapes as shown in  FIGS. 7A and 7B . As seen in  FIGS. 7A and 7B , the electrode  32  is mounted within resilient sleeve  31  such that when the resilient sleeve with damper portion  35  is deformed, a central axis passing through electrode  32  is maintained in a position approximately normal to a plane tangential to a scalp portion positioned beneath the electrode for self-orienting. 
     The EEG electrode  32  is positioned within the sleeve having distal ends/legs embedded in the annular groove  33  of the resilient sleeve  31 . Embedding the EEG sensing electrode  32  inside the self-orienting electrode sleeve  31  and fixing the orientation of cable  39  minimizes the possibility of EEG electrode dislocation. 
     At the portion of the resilient sleeve  31  directly adjacent to a patient&#39;s scalp, a cavity  34  is formed. This cavity is typically filled with a conductive gel to provide contact between the scalp and the electrode. Alternatively, a deformable conductive material can fill cavity  34  for provide the needed skin-electrode impedance. The annular edge of the resilient sleeve  31  can also be placed on the head comfortably and minimize the leakage from the electrode during head movement. The conductive gel can reduce the skin-electrode impedance between the EEG electrode  32  and scalp  80  of the head. This design can reduce the skin-electrode impedance to enhance the EEG signal quality. 
     Referring to  FIGS. 8 and 9 , the left segment  22  and right segment  23  of the EEG head-mountable device  181  can be bent upward and downward by mechanical fasteners (optionally formed by a hinge joint  61 ) during application and removal of device  181 . Advantageously, the relative movement of the sections to one another avoids deforming the electrode at the left segment  22  and right segment  23  of the EEG head-mountable device during application of the device. However, the electrode sleeve  31  will deform radially and self-orient at the desired electrode position on the patient&#39;s head (that is, with the central axis of the electrode substantially perpendicular to a line tangent to the scalp beneath the electrode). 
       FIG. 10  depicts left reference electrode  25  and right reference electrode  26  that are located at the auxiliary segment  24  of the head-mountable device  181 . The left reference electrode  25  and right reference electrode  26  can be adjusted along the axis at a selected angle to contact with the ear reference location. 
     Referring to  FIG. 11  and  FIG. 12 , the visual bio-feedback signal indicators  37  are incorporated in the electrode design to diffuse a color pattern on the light ring  36  which is placed outside of the device. The visual signal indicators can show the skin-electrode impedance value, the EEG value, or control parameters. The visual signal indicator can be one or more LEDs  37  with single or more colors. The color patterns and intensity represent impedance, EEG value or control parameters. The color is not limited to cover only the above pattern and parameters. 
     In order to provide better signal-to-noise ratio for the EEG signals, a pre-amplifier  40  can be attached physically close to each electrode. The amplifier  40  can be arranged in a single unit or in the form of an array. 
     As set forth above, the present invention provides an improved biofeedback device that is portable, easy-to-use, and minimizes the preparation time for brain training both in a hospital and home setting. While the foregoing invention has been described with respect to various embodiments and examples, it is understood that other embodiments are within the scope of the present invention as expressed in the following claims and their equivalents. Moreover, the above specific examples are to be construed as merely illustrative, and not limitative of the remainder of the disclosure. The disclosure of all cited references is incorporated by reference herein. 
     REFERENCES 
     
         
         1. R. Ball, C. Shu, P. C. Xi, M. Rioux, Y. Luximon, and J. Molenbroek, “A comparison between Chinese and Caucasian head shapes,” Applied Ergonomics, vol. 41, pp. 832-839, 2010 
         2. Z. Zhuang, S. Benson, D. “Viscusi. Digital 3-D headforms with facial features representative of the current U.S. work force,” Ergonomics; 53: 661-71,2010 
         3. China National Institute of Standardization. (1998) CNIS GB/T2428:1998. Head-face dimensions of adults by Xiao H, Hua D H, Yang T X, Zhang Z B, Bi G X, Liu J M. Beijing, China: General Administration of Quality Supervision, Inspection and Quarantine of the People&#39;s Republic of China. 
         4. China National Institute of Standardization. (1998) CNIS GB/T2428:1998. Head-face dimensions of adults by Xiao H, Hua D H, Yang T X, Zhang Z B, Bi G X, Liu J M. Beijing, China: General Administration of Quality Supervision, Inspection and Quarantine of the People&#39;s Republic of China. 
         5. China National Institute of Standardization. (1981) CNIS GB2428-81. Head styles of adults by Beijing Institute of Labor Protection. Beijing, China: General Administration of Quality Supervision, Inspection and Quarantine of the People&#39;s Republic of China. 
         6. Y. Yu, S. Benson, W. Cheng, J. Hsiao, Y. Liu, Z. Zhuang and W. Chen. “Digital 3-D Headforms Representative of Chinese Workers” Ann. Occup. Hyg., pp. 1-10, 2011
 
The disclosure of the foregoing cited references is incorporated herein by reference.