US 3882850 A
An electroencephalographic instrument for the bio-feedback of human brain waves within the Alpha and Theta frequency bands utilizes an adjustable headband electrode and a clip-on electrode as its pick-ups and earphones which provide an audible signal to the user. The circuitry of the instrument includes an active filter comprising a band-pass network and an operational amplifier, and an oscillator whose frequency is modulated by the active filter.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Bailin et al.
[ BRAIN WAVE FEEDBACK INSTRUMENT  Inventors: Howard Bailin, 725 E. 84th St.,
Brooklyn, NY. 11236; John Labenski, Stewartstown, Pa. 17363  Filed: May 9, 1973  App]. No.: 358,723
 US. Cl l28/2.l B
 Int. Cl A6lb 5/04  Field of Search 128/1 C, 1 R, 2.1 B; 307/301  References Cited UNITED STATES PATENTS 2,466,054 4/1949 Siebel 128/1 R 2,611,368 9/1952 Pecora .1
3,468,302 9/1969 Cowel1.....
3,498,287 3/1970 Ertl 128/2.1 B
[ 51 May 13,1975
3,602,215 8/1971 Parnell 128/2.06 B 3,658,054 4/1972 lberall l28/2.l B 3,665,223 5/1972 Stichweh et al.. 307/301 3,753,433 8/1973 Bakerich et a1. l28/2.1 B
Primary Examiner-William E. Kamm Attorney, Agent, or Firm-Eliot S. Gerber  ABSTRACT An electroencephalographic instrument for the biofeedback of human brain waves within the Alpha and Theta frequency bands utilizes an adjustable headband electrode and a clip-on electrode as its pick-ups and earphones which provide an audible signal to the user. The circuitry of the instrument includes an active filter comprising a band-pass network and an operational amplifier, and an oscillator whose frequency is modulated by the active filter.
8 Claims, 5 Drawing Figures PATENIED HAY 1 319. 5
SHEEI 2 OF 3 PATENTEDHAY 1 1915 SHEET 3 OF 3 QUE x H w T Q Q m X h m Q 5 X k M 1@ q & m f u I F 15 n N h H h wm H L R \1 QM BRAIN WAVE FEEDBACK INSTRUMENT BACKGROUND OF THE INVENTION The present invention relates to electroencephalographic instruments and more particularly to such an instrument providing to a subject an audible indication of brain waves within the Alpha and-Theta frequency ranges.
It has been known for some years that the brain produces electrical activity at the microvolt level. That I electrical activity has been detected, amplified and recorded, usually using stylus-type recordings, and such recordings have been studied, for example, as an indication of neurological damage. The awake brain waves have been categorized according to the predominant frequency of the waves as Alpha, which is 7.5-1 3 cycles per second (Hz); Beta, which is 13-28 cycles per second; and Theta, which is 3.5-7.5 cycles per second.
The deepest state of sleep is characterized by waves of high amplitude and low frequency, called Delta waves. On the other side of the spectrum, when one is in a normal awake and alert state, the brain produces waves of very high frequency and low amplitude, called Beta waves.
But if one relaxes and lets his attention drift downward, the brain will produce bursts of high amplitude, low frequency (7.5-13 cycles per second) Alpha waves. A high degree of Alpha activity the Alpha state is often recorded in individuals during Yoga and Zen meditation.
A few years ago it was determined that it was possible for some, but not all, human subjects undergoing tests to modify certain of their autogenic muscular and other body activity by means of bio-feedback. In this sense biofeedback is a rough analogy derivedfrom the electrical engineering term positive feedback to indicate that an individual who is able to monitor certain of his autogenic responses becomes able, over time, to consciously control those responses. For example, some of the earlier work in this field had to do with temperature gradients between the forehead and the hand. An individual watched a meter which indicated that temperature gradient and, within a relatively short period of time, for example, one or two days, by varying their internal thought processes, for example, their internal imaging, some subjects were able to consciously control that temperature difference. Some subjects were able, after a period of training, to raise the temperature of their hand by a measurable and repeatable amount. That particular experiment has proven fruitful in some instances in relieving individuals of migrain headaches, which are believed to be associated with blood flow in certain regions of the brain.
It has been shown, by a series of experiments, that not only can human subjects learn to identify the Alpha and non-Alpha states, but experiments have shown that many are able to control their minds to the extent of entering and sustaining either state upon command.
The original problem was finding easy and less timeconsuming methods for teaching subjects brain-wave control. The answer was to devise an instrument that would translate the occurrence of Alpha. waves, as measured by the EEG machine, into a tone or tone change. Each time a subject produces Alpha waves, he simultaneously generates a tone or tone change. When he stops, the tone or tone change also stops. The subject had only one task: find some way to keepthe tone change audible for as long as possible. As it turns out, many persons trained in this manner can learn to produce Alpha at will in a relatively short period of time.
In the past few years, the research on training brain waves has accelerated. Not only Alpha, but Beta, Theta and even Delta have come under voluntary control, at least in the laboratory. The machinery has also been modified. In certain instruments, tone can be amplified to indicate increases in brain-wave intensity, or it can be replaced by another form of feedback, such as light. However, such instruments, may be relatively complex or expensive. The basic technique, however, remains the same: the brain-wave impulses, which elude our normal consciousness, are piped through EEG machine electrodes, amplified by delicate circuitry and finally translated into light, sound or some other medium that is accessible to the senses. Once turned into himself, almost anyone can learn to identify specific brain-wave states and, in short order, to control them.
If specific brain waves are associated with specific states of consciousness, why does one need feedback? If one is in the Alpha state he should be able to experience it directly. Why does one need this elaborate biofeedback setup to tell us what we are feeling? There are two answers to this question. First, a surprising number of people really do not know what they are feeling. Our culture does not teach us to develop the sensitivity needed to detect subtle shifts in our emotional chemistry. To feel means to be aware, but most feel by jolting their nervous systems beyond the conditioned state of civilized numbness with television, drugs, alcohol and loud music. These devices stimulate, but in the long run they may reduce the ability to feel.
Second, brain-wave experiences are not the same in all individuals. While brain waves can be measured objectively by the number of cycles the brain generates per second, the subjective experience of particular frequencies varies according to the individual. If one has Alpha, it may mean a good state or it may just mean so many cycles per second. One persons experience of Alpha can be another persons experience of Theta. Although Alpha is usually correlated with feelings of relaxation and well-being, this is not always the case. For some people, the production of Alpha can even be an upsetting experience. They have spent so much of their time keeping busy that slowing down from Beta into Alpha is a source of anxiety and apprehension. The effects of bio-feedback training apply to the statistical majority; they are not universal.
It has been found that the obtaining of Alpha control is an evolutionary process with many subjects. For the first few sessions they may experience relatively little Alpha and only some subjective feeling that Alpha is real. However, as more control is gained, gradually over a period of practice, their skill may improve; and with sufficient practice they finally achieve a control which may be objectively ascertained by use of the machine of the present invention. Eventually with some subjects the Alpha state will be so obvious and secondnature that they will not need the machine to produce that state.
Although it has been indicated by many subjects that the Alpha state is relaxing and pleasant, such reaction is by no means uniform since some subjects simply report it as interesting and curious and some subjects report it as being associated with no special feeling.
It has been hypothesized, although not proven, that Theta rhythms are related to such deep unconscious activity as inner visualization, memory, imagery and creativity.
The machine of the present invention, as other biofeedback machines, does not produce Alpha activity but rather indicates the presence or absence of such brain waves. By knowing when Alpha activity brain waves is or is not present, the subject quickly learns some degree of control over those brain waves.
SUMMARY OF THE INVENTION The instrument of the present invention provides biofeedback by giving an audible signal to the user. That audible signal is a constant background hum which changes in frequency, that is, it changes in sound when the subjects brain is producing Alpha waves so that the subject can learn to identify or later increase or suppress Alpha wave patterns. The same machine, by a switch on its control panel being switched to an alternative position, can help the subject to identify Theta waves.
A first electrode, attached to an adjustable headband, is placed on the subjects head, preferably occtipally, using a conductive disk electrode. A second electrode is clipped to the ear. The electrodes are removably connected to a control instrument which has a combined on-off and volume control and also a switch for selecting Alpha or Theta waves. The circuitry within the control instrument includes a high-gain lownoise transistor, an operational amplifier, a band-pass network and a unijunction device which acts as an oscillator. The output is to a jack in which headphones or a tape recorder may be connected.
OBJECTIVES OF THE INVENTION It is an objective of the present invention to provide a bio-feedback instrument which will amplify Alpha or Theta brain waves and provide an audible signal indicating such waves without interference from eye movements.
It is a further objective of the present invention to provide such an instrument which is relatively simple in construction, low in cost and will be not subject to frequent repairs or factory adjustments.
It is a further objective of the present invention to provide such an instrument which utilizes a single 9- volt battery so that the circuitry may be less complex and the problem of replacing the battery may be less troublesome.
It is a further objective to provide such an instrument in which the output may be a tone which changes its characteristics and may be heard through an earphone or either simultaneously or alternatively to the earphone may be recorded on a tape recorder.
BRIEF DESCRIPTION OF THE DRAWINGS Other objectives of the present invention will be apparent from the detailed description set forth below, taken in conjunction with the accompanying drawings.
In the drawings:
FIG. 1 is a perspective view of the bio-feedback device of the present invention, showing the earphones, the headband with its associated electrode, and the control instrument;
FIG. 2 is a detailed schematic drawing of the circuitry of the control instrument;
FIG. 3 is a detailed schematic circuit diagram of a modified input stage in which the other portions of the circuitry of FIG. 2 are not changed;
FIG. 4 is a detailed schematic circuit diagram of an alternative output stage of the circuit of FIG. 2, in which the other portions of the circuitry of FIG. 2 are not changed; and
FIG. 5 is similar to FIG. 2 and presents an alternative circuit for the control instrument.
As shown in FIG. 1, the device of the present invention includes a headband 10 which is adjustable and which preferably is of a somewhat stretchable woven material. The headband has, on its inner face on one end and on its outer face on the opposite end, a material such as Velcro, trademark of American Velcro, Inc., which is removably selfadherent, or a series of snaps. This enables the headband to be placed around the subjects head, adjusted and readily fastened thereon. A metal electrode disk contactor 12 is secured to the headband. A wire 13, which is electrically insulated, leads from the electrode 12 to ajack which is removably plugged into the control instrument 14. A second wire 15, which is also electrically insulated, leads from that same jack plugged into the control instrument 14 to a spring-loaded clip electrode 16. The electrode 16 is adapted to be removably clipped to the subjects earlobe. This arrangement greatly reduces the adverse effects of eye motion.
The control instrument 14 is a small rectangular box. It has a second input jack 17 which is adapted to re movably receive a male plug 18 connected to an insulated wire 19 leading to a crystal earphone 20. The crystal earphone is an electromagnetic transducer which converts electrical waves into an audible sound. The audible sound produced by the earphone 20 is conducted, by the pair of hollow tubes 21 and 22, to the subjects ears, the ends of the tubes 21 and 22 being adapted to be inserted in the subjects ears.
The control instrument 14 has a rotatable knob 25 which may be placed in the of position or alternatively may be clicked to the on position and rotated clockwise to both activate the instrument and to control the volume. A toggle switch 23 protrudes from the face 24 of the instrument and has two opposite positions labeled alpha and theta. These two positions of the toggle switch 23 correspond to picking up and amplifying respectively the Alpha or Theta waves.
As shown in the detailed schematic drawing of FIG. 2, the circuitry of the control instrument 14 is relatively simple so as to be low in cost and require little or no maintenance. The power for the device is obtained from a 9-volt dry cell battery 30, which is preferably of the conventional transistor radio type. The negative terminal of the battery 30 is grounded, that is, the negative lead which is a removable cap is soldered to a line which acts as the ground line of the circuit board. The second removable cap is connected to a wire 31 which leads to the on-off switch 32. This on-off switch 32 is the same switch as the switch 15 and is ganged to the volume control 33, which volume control 33 uses a conventional rotatable adjustable resistor (potentiometer) 34. The switch 32 is connected by line 35 to one end of a resistor 36 (470 K ohms) and also to one end of a resistor 36a(3.9 K ohms) and also to the input terminal 7 of the operational amplifier 38.
The operational amplifier 38 is preferably a linear integrated circuit and may be of the type UA74lCV (former No. N574-1V), which is a high performance operational amplifier having high open loop gain, internal compensation, high common mode range and temperature stability. It is used in the T-package with pin 2 being an inverting input, pin 3 the non-inverting input, pin 6 the output, pin 7 the positive voltage (from battery 30) and pin 4 the negative voltage (the ground connection). The operational amplifier 38 is biased for single-ended operation, that is, it is biased by its connecting biasing resistors for operation in about the center of the voltage of the battery cell.
The opposite end of the resistor 36 is connected to a capacitor 37 (0.005 MFD) and to the terminal A of the unijunction device 39. The unijunction device 39 is preferably a PNPN transistor and may suitably be of the type D13T1 available from General Electric. The type D13T1, called a programmable unijunction transistor PUT, is a three-terminal planar passivated PNPN device whose terminals are designated anode (A), anode gate ((3) and cathode (K).
The output of the unijunction device 39 is connected by line 39a to the previously mentioned potentiometer 34 K ohms) whose opposite end 40 is grounded.
A female inputjack 51) is provided. One line 51 to the jack 50 leads to the ground and to a resistor 52 (680 K ohms). The other jack terminal is connected by the line 52a to one end of the capacitor 53 (5 MFD), the opposite end of the capacitor 53 being connected to the base of the low-noise high-grade transistor 54. For example, transistor 54 is of the type 2N5828, which is an NPN silicon transistor. That transistor type 2N5 828 is a planar, passivated, epitaxial transistor which amplifies signals at the audio range with good gain linearity at the microvolt level.
The collector 55 of the transistor 54 is connected to one end of the resistor 56 (27 K ohms) and to one end of the resistor 57 (5.6 megohms). The emitter of transistor 54 is connected to one end of the resistor 58 K ohms), whose other end is grounded, and also to one end of the capacitor 59a (100 MFD), whose opposite terminal is grounded. A common connection point 60 (between capacitor 53 and transistor 54) is also connected to resistor 61 (1.2 megohms), whose opposite end is connected to capacitor 62 (100 MFD). The opposite side of that capacitor 62 is also grounded. The input to pin 2 of the operational amplifier 38 is from a network consisting of a resistor 65 (5.6 megohms), a capacitor 66 (0.015 MFD), and a capacitor 67 (0.22 MFD). That network is connected between the input 2 of the operational amplifier 38 and its output 6. The output 6 is connected to a resistor 68 (11 K ohms) whose opposite terminal is connected to the G terminal of unijunction device 39.
All of the above-mentioned components are utilized in connection with the amplification and filtering of the Alpha waves. However, in addition, the instrument will selectively amplify and filter the Theta waves by changing of position of the toggle switch 23. The toggle switch 2.3 closes the contacts 23a and 23b to add in the components shown in dashed lines. T hcse components are the capacitor 70 (0.22 MFD), which is placed in parallel with the capacitor 67, and also the capacitor 71 (0.015 MFD), which is placed in parallel with the capacitor 66. A common junction '72 between capacitors 66 and 6'7 is connected through the resistor 73 (12 K ohms) to ground 74.
As shown in FIG. 2, the input is to the jack 50 and either the head electrode 12 or the ear electrode 16 may be connected to either of the lines 52a or 51. The capacitor 53 prevents direct current from reaching the subjectand the resistors 61 and 52 bias the transistor 54. The output of the transistor 54 is to the filtering network comprising resistor 57 and capacitor 5912 which cuts off past 10 cycles, thereby attenuating or eliminating any 60 Hz hum which may be picked up from power lines in the vicinity.
The band-pass filter (the network for alpha waves) consists of resistors 65 and 73 and capacitors 67 and 66. When the ganged switch 23a and 23b is thrown, so that those switch contacts are set for Theta waves, the capacitors and 71 are added to the network.
The band-pass network sets the center of the bandpass filter which, for Alpha waves, is at 10 cycles. With the switch contacts 23a and 23b closed for Theta waves, the center of the band-pass filter is at 5 cycles. The network also determines the band width, which width for Alpha frequencies is at 2 cycles and at Theta frequency is at 1 cycle. In both cases the network also sets the closed loop gain as the band-pass network, together with the operational amplifier, comprises an active filter.
The resistor 68, which is connected to the output pin 6 of the operational amplifier 38, programs the unijunction device 39, that is, the characteristics of the unijunction device 39 are modified by the value of the resistor 68. The unijunction device with its associated bias resistor 36 and capacitor 37 constitutes a freerunning oscillator.
In operation, when there is a voltage at pin 6, the v voltage battery 30 through resistor 36 charges up the capacitor 37. When the voltage at the anode gate A reaches the threshold voltage, which is approximately the voltage at pin 6, then the voltage which has been stored at capacitor 37 is discharged through the unijunction device 39 to the variable resistor 34. Once that discharge has occurred, which is seen at the output line 33 as an electrical wave and which is heard at the earphone as a hum, then the voltage again starts to build up through resistor 36 upon capacitor 37. 1f the voltage at the gate G is made higher, then the frequency decreases. Such a change of frequency occurs when Alpha waves are received at the input jack 50 and amplified, thereby providing an output at pin 6 of the operational amplifier 38. The background oscillation is the normal oscillation of the unijunction device and its associated circuit of about 1000 cycles. The modulating frequency at pin 6 is a sinusoidal wave at 10 cycles frequency. Consequently, there are two separate effects resulting from the presence of Alpha wave input. First, there is a sinusoidal output at pin 6 of the operational amplifier, which 1) modulates the normal oscillation of the unijunction device and (2) provides a degree of amplitude modulation due to the changes of voltage at pin 6. In the second effect, the strength (amplitude) of the Alpha wave, as distinct from its frequency, gives a different amplitude modulation which can be heard, resulting from the higher voltages produced at pin 6.
As shown in FIG. 3, the single input transistor 54 of FIG. 2 may alternatively be replaced by a series of transistors in order to obtain additional gain and sensitivity. The portions of the circuit which are the same have been labeled with prime numbers. It will be seen that the transistor 54 has its output at the collector 55' connected to the base 80 of the second transistor 81. The collector 82 of the second transistor is connected to the resistor 57' (corresponding to resistor 57). In addition, suitable biases on the second transistor 81 are provided by resistors 83 and 84 and 85. The sensitivity of the device may be set by the variable resistor 86.
An alternative output stage, as shown in FIG. 4, comprises a transformer 91 which is in parallel with the variable resistor (potentiometer) volume control switch 34 (shown in FIG. 2). As shown in FIG. 4, the transformer 91 has its primary 90 connected to the cathode K of unijunction device 39.
The secondary 92 of the transformer 91 is connected to a jack into which may be plugged a tape recorder or a set of earphones. The extra earphones may be those of a monitoring teacher and the users earphones 93 are connected directly to the primary 90, see FIG. 4. The transformer 91 acts as an output for isolation purposes when using an A.C. operated device such as a tape recorder or audio amplifier.
A further modification is shown in FIG. 5. The numbers of the parts shown in FIG. 2 are the same, except that prime numbers are used to indicate corresponding parts. In the circuit of FIG. 2 and FIG. 4, the transistor 54' is preferably of type 2N5089 and the operational amplifier 38 is one-half of integrated circuit type 5558, a dual operational amplifier available from Motorola. The other half, i.e., the other operational amplifier 101, is used as the free-running oscillator. The amplifiers input at pin 5 is connected, by resistor 102, to its output 103 (pin 7). Its input at pin 6 is connected, by resistor 104, and optional tone control 105 to output 103 and grounded through capacitor 106. The frequency of the free-running oscillator is varied (modulated) from the line having resistor 67.
1. A brain wave bio-feedback instrument comprising an adjustable headband, an electrode supported by said headband, a second electrode, means for clipping the second electrode on a subjects ear and including a spring-operated clip, a control device, a first switch mounted on said control device, a single battery cell positioned within said control device and connected to said first switch and to a ground, an operational amplifier having an input and an output, means connecting one of said electrodes in series with said operational amplifier input, means connecting the other electrode to ground, a set of biasing resistors connected to said operational amplifier and biasing said operational amplifier for operation at about the mid-point of the voltage of said battery cell, a resistor-capacitor band-pass means connected between the input and output of said operational amplifier and comprising an active filter network with said operational amplifier, a voltage controlled oscillator, said voltage controlled oscillator being connected to the output of said operational amplifier so that the oscillators frequency is thereby modulated by the output voltage of said operational amplifier, a sound transducer connected to said voltage controlled oscillator, and a second switch mounted on said control device to provide selection between Alpha and non-Alpha waves and connected to said band-pass means to selectively alter the operating elements of said band-pass means.
2. An instrument as in claim 1 wherein said voltage controlled oscillator comprises a single active device which is a programmable unijunction transistor having an anode, an anode gate and a cathode, wherein said anode gate is connected to the output of said operational amplifier and the cathode is connected to the sound transducer and the anode is connected in series with the battery cell.
3. An instrument as in claim 2 and further comprising a variable resistor connected between said cathode and said ground which variable resistor operates as a volume control.
4. An instrument as in claim 1 wherein said voltage controlled oscillator includes a second operational amplifier having its input and output connected to a resistor-capacitor network.
5. An instrument as in claim 4 wherein said two operational amplifiers are formed as linear integrated circuits on a single chip.
6. An instrument as in claim 1 wherein an amplifier which is a low noise high-gain device is connected between one of the said electrodes and the input of said operational amplifier and the battery cell.
7. An instrument as in claim 1 wherein a complementary pair of transistors is connected in cascade between said device input and said operational amplifier input.
8. An instrument as in claim 1 wherein the sound transducer is an earphone and connected thereto a pair of tubular earphones.