| United States Patent |
5,935,054
|
|
Loos
|
August 10, 1999
|
Magnetic excitation of sensory resonances
Abstract
The invention pertains to influencing the nervous system of a subject by a
weak externally applied magnetic field with a frequency near 1/2 Hz. In a
range of amplitudes, such fields can excite the 1/2 sensory resonance,
which is the physiological effect involved in "rocking the baby". The wave
form of the stimulating magnetic field is restricted by conditions on the
spectral power density, imposed in order to avoid irritating the brain and
the risk of kindling. The method and apparatus can be used by the general
public as an aid to relaxation, sleep, or arousal, and clinically for the
control of tremors, seizures, and emotional disorders.
| Inventors:
|
Loos; Hendricus G. (3019 Cresta Way, Laguna Beach, CA 92651)
|
| Appl. No.:
|
486918 |
| Filed:
|
June 7, 1995 |
| Current U.S. Class: |
600/9 |
| Intern'l Class: |
A61N 002/00 |
| Field of Search: |
600/9-15
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
P. Lindemann, The Megabrain Report, vol. 1, #2, pp. 34-35 (1990).
P. Limdemann, The Megabrain Report, vol. 1, #1, pp. 30-31 (1990).
|
Primary Examiner: Lacyk; John P.
Claims
I claim:
1. Apparatus for excerting an influence on the nervous system of a nearby
subject, in the presence of atmospheric air currents, the apparatus
comprising:
mechanical oscillator;
aerodynamic excitation means for providing excitation of the mechanical
oscillator in response to said atmospheric air currents;
permanent magnet means for providing a magnetic dipole, the magnetic dipole
having an orientation;
mounting means for mounting the permanent magnet means onto the mechanical
oscillator in such a manner that said excitation causes a fluctuation of
the orientation of the magnetic dipole;
whereby a time-varying magnetic field is produced in the subject.
2. Apparatus according to claim 1, further including tuning means for
tuning the mechanical oscillator.
3. A method for influencing the autonomic nervous system of a subject,
comprising:
applying to the subject a periodic magnetic field with a frequency in the
range 0.1 to 1 Hz and an amplitude in the range 5 femtotesla to 50
nanotesla;
determining, through manual frequency scanning, a frequency at which the
subject experiences ptosis of the eyelids, the last said frequency being
called the ptosis frequency; and
setting the field frequency to a value in the range from 20% below to 10%
above the ptosis frequency;
whereby said periodic magnetic field will influence the autonomic nervous
system of the subject.
4. Apparatus for exciting in a subject the 1/2 Hz sensory resonance having
at a resonance frequency, the apparatus comprising:
generator means for generating a time-varying voltage with a dominant
frequency in the range 0.1 to 1 Hz;
coil means, connected to the generator means, for inducing in the subject a
magnetic field;
tuning means for tuning the dominant frequency to said resonance frequency.
5. Apparatus according to claim 4, wherein the coil means comprise a
multipole coil for inducing a localized magnetic field.
6. Apparatus according to claim 5, wherein said multipole coil includes
distributed windings for limiting the exposure of the subject to the
magnetic field.
7. Apparatus according to claim 4, also including:
control means for automatically controlling the time-varying voltage.
8. A method for exciting in a subject the 1/2 Hz sensory resonance having
at a resonance frequency, the method comprising the steps of:
generating a time-varying voltage with a dominant frequency in the range
0.1 to 1 Hz;
connecting the time-varying voltage to a coil; and
tuning the dominant frequency to said resonance frequency.
Description
BACKGROUND OF THE INVENTION
The human nervous system exhibits a sensitivity to certain low-frequency
stimuli, as is evident from rocking a baby or relaxing in a rocking chair.
In both cases, the maximum soothing effect is obtained for a periodic
motion with a frequency near 1/2 Hz. The effect is here called "the 1/2 Hz
sensory resonance". In the rocking response, the sensory resonance is
excited principally by frequency-coded signals from the vestibular organ.
However, the rocking motion also induces body strains, and these are
detected by stretch receptors such as Ruffini corpuscules in the skin and
muscle spindles throughout the body. In addition, signals may come from
cutaneous cold and warmth receptors which report skin temperature
variations caused by relative air currents induced by the rocking motion.
All these receptors employ frequency coding in their sensory function, and
it is believed that their signals are combined and compared with the
vestibular nerve signals in an assessment of the somatic state. One may
thus expect that the resonance can be excited separately not only through
the vestibular nerve, but also through the other sensory modalities
mentioned. This notion is supported by the observation that gently
stroking of a child with a frequency near 1/2 Hz has a soothing effect as
well. Appropriate separate stimulation of the other frequency-coding
sensory receptors mentioned is expected to have a similar effect.
The notion has occurred that frequency-coding sensory receptors may perhaps
respond to certain artificial stimulations, and that such stimulations
could be used to cause excitation of the 1/2 Hz sensory resonance. This
indeed can been done, by using externally applied weak electric fields as
the artificial stimulus, as discussed in the U.S. patent application Ser.
08/447,394 1!. Autonomic effects of this stimulation have been observed
in the form of relaxation, drowsiness, sexual excitement, or tonic smile,
depending on the precise electric field frequency near 1/2 Hz used. The
question whether the effects are perhaps due to the direct action of the
electric field on the brain has been settled by experiments in which
localized weak electric fields are applied to areas of the skin away from
the head; these experiments showed the same array of autonomic effects. It
follows that the electric field acts on certain somatosensory nerves.
A major application of the electric exitation of the resonance is seen in
the form of a sleeping aid. The method can further be used by the general
public as an aid to relaxation and arousal, and clinically for the control
of tremmors and seizures as well as disorders resulting from malfunctions
of the autonomic nervous system, such as panic attacks.
Electric fields are subject to polarization effects that bar certain
applications. These limitations would be circumvented if the excitation
could be done by magnetic rather than electric fields. It is an object of
the present invention to provide a method and apparatus for excitation of
the 1/2 Hz sensory resonance by oscillatory magnetic fields.
An electromagnetic field apparatus for environmental control is discussed
by Grauvogel in U.S. Pat. No. 3,678,337. The apparatus is to re-create
indoors the electric and magnetic fields that occur naturally
out-of-doors, in the interest of physical and mental well-being. In
advancing this notion, Grauvogel overlooks the fact that the earth's
magnetic field is not shielded by buildings; therefore, the magnetic part
of his apparatus is superfluous in the context of his objective. In
Grauvogel's claims, the field of use is stated as "environmental control
apparatus".
In U.S. Pat. No. 4,197,851 Fellus shows an apparatus for emitting
high-frequency electromagnetic waves with a low intensity such as to avoid
significant thermal effects in exposed tissue, employing an "antenna"
which is applied closely to the skin via insulation material, in such a
manner as to conform to body contours. Bentall, in U.S. Pat. No. 4,611,599
shows an electrical apparatus for influencing a metabolic growth
characteristic, wherein a radio frequency electromagnetic field is applied
to a subject at a low power level such as not to produce bulk heating of
the exposed tissue. The high-frequencies used by Fellus and by Bentall are
not suitable for exciting the 1/2 Hz sensory resonance.
A device for influencing subjects by means of pulsed electromagnetic fields
has been discussed by Lindemann 2!. His "Centron" device comprises a
square wave generator connected to an equiangular spiral coil with two
branches. The pulse rate can be chosen from 12 discrete frequencies
ranging from 1 to 18 Hz. Comments on the workings of the spiral coil are
given by Lindeman 3! in the context of "scalar fields", a notion that
happens to be in conflict with modern physics. According to Lindeman 3!,
the spiral coil of the Centron involves "a high degree of interaction
between the inductance and capacitance, creating what is called a scalar".
In spite of the erroneous physical basis presented, the Centron device may
indeed affect the nervous system. However, several shortcomings are
apparent in the design. First, the spiral coil is woefully inefficient and
is therefore wasteful of electric current, a precious commodity in
battery-operated devices. It may perhaps be thought that the spiral coil
design provides localization of the magnetic field by clever
cancellations, but that is not the case; a calculation of the steady
asymptotic magnetic field induced by the coil shows that the far field is
dominated by a dipole. Second, the frequency range of the device misses
the 1/2 Hz sensory resonance alltogether, and the use of preset discrete
frequencies hampers exploration of other resonances. Last but not least,
the fundamental frequencies and some of the higher harmonics in the square
wave produce nuisance signals in the brain, and pose a risk of kindling
4! in subjects with a disposition to epilepsy.
It is an object of the present invention to provide an efficient
battery-powered device for inducing magnetic fields for the excitation of
the 1/2 Hz sensory resonance without causing irritation to the brain or
posing a threat of kindling.
Other devices that emit "scalar" fields for unspecified therapeutic
purposes are the Teslar watch and the MicroHarmonizer, distributed by
Tools For Exploration in San Rafael, Calif. The Teslar watch emits a
pulsed magnetic field at a fixed frequency of 7.83 Hertz, and the
MicroHarmonizer can be switched to either 7.83 Hz or 3.91 Hz. Neither
device can be tuned to the 1/2 Hz sensory resonance.
There is much public concern about the health effects of low-frequency
electromagnetic fields. In response, governments have issued guide lines
for manufacturers of electronic equipment. Among these, the Swedish MPRII
guide lines are the strictest in the world. For human exposure to
low-frequency magnetic fields, MPRII calls for an upper limit of 250 nT in
the frequency band from 5 Hz to 2 KHz, and 25 nT in the band from 2 KHz to
400 KHz. In the topical application of localized magnetic fields by coils
placed close to the skin, compliance with the MPRII guidelines may require
use of a distributed coil, in order to keep the spatial maximum of the
field from exceeding the MPRII limit. It is yet a further object of the
present invention to provide distributed coils that induce localized
magnetic fields.
The brain adapts to nuisance signals by plasticly changing neural
circuitry, such as to block these signals from further processing. This
effect has been noticed in electric field therapy of insomnia, where the
effectiveness of a fixed frequency field wears off after several nights of
application. It is an object of the present invention to provide a
magnetic field with characteristics such as to minimize this adaptive
effect.
SUMMARY
The vestibular nerves and several other types of somatic sensory nerves
detect bodily motion, and code the information as frequency modulation
(FM) of stochastic firing rates. These sensory signals can excite a
resonance in the central nervous system, as is seen from the soothing
effect of rocking a baby with a frequency near 1/2 Hz. The present
invention provides a method and means for exciting this sensory resonance
by application of an oscillatory external magnetic field with a dominant
frequency near 1/2 Hz. It appears that such magnetic fields cause a weak
frequency modulation of the firing rates of certain sensory receptors,
most likely the vestibular end organ and muscle spindles. The resulting
weak FM signals in the afferents from these receptors affect the central
nervous system in much the same manner as a subliminal rocking motion.
For a sustained noticible effect the magnetic field intensity must be
chosen such as to cause weak FM signals that have signal-to-noise ratios
such that the signals go unchecked by nuisance-blocking circuitry, while
still being strong enough to influence the autonomic nervous system
through a resonance in certain critical neural circuitry. From
experiments, this requirement on the signal-to-noise ratio appears to be
met by magnetic field amplitudes in the range from 5 femtotesla to 50
nanotesla. Several different results can be obtained, such as relaxation,
sleep, and sexual excitement, and control of tremors, seizures, and panic
attacks, depending on the field application site and the frequency used.
The magnetic field may be produced by a coil connected to a voltage
generator. It is important to curtail higher harmonics of the magnetic
field wave form such as not to irritate the brain or pose a threat of
kindling. To this end, the output wave form of the voltage generator must
be subjected to a restriction, here phrased in terms of the spectral power
density function.
For topical magnetic field application one needs coils which induce
magnetic fields that fall off rapidly with distance. A design procedure
for such multipole coils is discussed. A method is also provided for the
design of multipole coils for which the windings are distributed in order
to assure compliance with MPRII, when the coil is deployed close to the
skin.
A magnetic field of desirable characteristics for inducing relaxation or
sleep can also be generated by a mechanical apparatus that is driven by
naturally occuring air motions or drafts. An embodiment comprises a
permanent magnet that is mounted in the hollow of a sperically domed shell
to which is fastened a silk flower on a stem of appropriate length, such
as to give a natural rocking frequency near 1/2 Hz. Small air drafts cause
the assembly to rock slightly, thereby tilting the magnet in an
oscillatory motion. As a result, the magnetic field induced by the magnet
has a flucuating component, which excites in nearby subjects the 1/2 Hz
sensory resonance, if the device is properly tuned. The tuning is done by
slightly doming, by an adjustable amount, the surface that supports the
domed shell of the rocking assembly.
The invention lends itself to an embodiment as a nonlethal weapon which
remotely induces wooziness in foes. The embodiment comprises a permanent
magnet that is rotated by electric motor action by means of coils
energized by a battery-powered pulse circuit tuned to a frequency
appropriate to the 1/2 Hz sensory resonance. The activity and frequency
schedule can be controlled by a programmable processor.
In social settings it is desirable to have the voltage generator and the
coil contained in a single case, such as an eye shadow box. A compact
magnetic field generator of this type can be carried in a purse or
trousers pocket.
DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the preferred embodiment for topical application of an
oscillating magnetic field for ecxitation of the 1/2 Hz sensory resonance.
FIG. 2 shows a multipole coil for the generation of a localized magnetic
field.
FIG. 3 shows a distributed coil for close proximity topical magnetic field
application.
FIG. 4 shows a near-sine wave generator with automatic shutoff.
FIG. 5 shows an embodiment that generates a chaotic magnetic field.
FIG. 6 shows transitions of a chaotic square wave.
FIG. 7 shows the power spectrum of the magnetic field produced with the
generator of FIG. 5.
FIG. 8 shows an aero-mechanical embodiment for generating a fluctuating
magnetic field for inducing relaxation and sleep.
FIG. 9 shows an embodiment as a nonlethal weapon for projecting an
oscillating magnetic field to cause drowziness in a foe.
FIG. 10 shows a compact embodiment in a hinged eye shadow box.
DETAILED DESCRIPTION
It has been found in our laboratory that a weak oscillatory external
magnetic field can be used to excite the 1/2 Hz sensory resonance.
Sinusoidal magnetic fields with an amplitude between about 5 femtotesla
and 50 nanotesla have been observed to induce ptosis of the eyelids,
relaxation, sleepiness, a "knot" in the stomach, a soft warm feeling in
the stomach, a tonic smile, sudden loose stool, and sexual excitement,
depending on the precise frequency used, the part of the body exposed, and
the strength and duration of the field application. The frequencies that
gave these effects are all close to 1/2 Hz. The effects are experienced
after the subject has been exposed to the field for an extended time,
ranging from minutes to hours. Even for optimum field frequency, the
effects have been observed only for weak fields with amplitudes roughly in
the range from 5 femtotesla to 50 nanotesla.
Human sensitivity to such weak magnetic fields with frequencies near 1/2 Hz
is not understood, and appears to be in conflict with present
neuroscience. However, the effects have been observed repeatedly and
consistently over a period of a year and a half, in experiments in which
the inventor served as the subject. The experiments may be briefly
summarized as follows.
In the experiments, ptosis of the eyelids was used as a practical indicator
for autonomic response. When voluntary control of the eyelids is
relinquished, the eyelid position is determined by the autonomic nervous
system 4!. There are two ways in which the indicator can be used. In the
first, the subject simply relaxes control over the eyelids, and makes no
effort to correct for any drooping. The more sensitive second method, here
called "the eyes-up method", requires the subject to first close the eyes
about half way. While holding this position, the eyes are rolled upward,
while giving up voluntary control of the eyelids. With the eyeballs turned
up, ptosis will decrease the amount of light admitted to the eyes, and
with full ptosis the light is completely cut off. The second method is
very sensitive because the pressure exerted on the eyeballs by partly
closed eyelids increases parasympathetic activity. As a result, the eyelid
equilibrium position becomes somewhat labile, a state that is easily
recognized by eyelid flutter. The labile state is sensitive to very small
shifts in the activities of the sympathetic and parasympathetic systems.
The method works best when the subject is lying flat on the back and is
facing a blank light color wall that is dimly to moderately lit.
The frequency at which ptosis is at a maximum is here called the ptosis
frequency. It can be measured rather accurately with the eyes-up method,
and it serves as a characteristic frequency for the 1/2 Hz sensory
resonance. The frequencies at which the mentioned effects have been
observed lie in the range from 20% below to 10% above the ptosis
frequency. Although the ptosis frequency depends on the state of the
nervous and endocrine systems, it always is near 1/2 Hz. It also has been
found that the ptosis frequency is subject to a downward drift, rapid at
first and slowing over time. The ptosis frequency can be followed in its
downward drift by manual frequency tracking aimed at keeping ptosis at a
maximum. Eventually the frequency settles to a steady value, after about
10 minutes of field application. The frequency for an early ptosis,
typically 0.53 Hz, can be maintained in an approximately steady state by
turning the field off as soon as the ptosis starts to decrease, after
which the ptosis goes through an increase followed by a decline. The field
is turned back on as soon as the decline is perceived, and the cycle is
repeated.
The temporal behavior of the ptosis frequency is found to depend on the
amplitude of the applied oscillatory magnetic field. At the low end of the
effective intensity range, the ptosis frequency shift is less for smaller
field amplitudes, and the shift becomes imperceptible at very weak fields
of 5 femtotesla or so, where a faint ptosis can still be detected by a
perceptive subject. The high end of the tentative effective intensity
range has not been explored in this regard.
Use of square waves rather than sine waves for the time dependence of the
magnetic field gives somewhat similar results, but there is a peculiar
harsh feeling that is absent for sine wave stimulation. The harsh feeling
is attributed to strong higher harmonics in the square wave.
The results have been obtained with systemic field applications as well as
with topical applications of a localized magnetic field, either
administered to the head or to body regions away from the head.
Applications of sharply localized weak fields to body regions far away
from the head show that the magnetic field acts on somatosensory nerves.
The effects induced by magnetic field application over an extended time
interval often linger for as much as an hour after ending the application
This suggests that the endocrine system is affected.
Experiments of magnetic field therapy for mild insomnia have been conducted
for over 200 nights, using a variety of generators and coils. Among the
various wave forms the sine wave has given the best results when used with
very low field amplitudes, of the order of 10 femtotesla, applied to the
lower lumbar region of the body. A typical frequency used in these
experiments is 0.49 Hz. A virtue of the very small field amplitudes is
that adaption to the stimulus is at a minimum, so that the treatment
remains effective over many nights. Adaption is further mimimized by using
multipole magnetic fields. Such fields are sharply localized, and they
have strongly nonuniform spatial distributions. As a result, the evoked
signals received by the brain from the various parts of the body are
strongly nonuniform and localized. As a consequence, changes in sleep
position cause a large variety of sensory patterns, with a limited
duration for each individual pattern. An other successful approach for
keeping down adaption is to limit the magnetic field application to half
an hour or so; larger field strengths can then be used.
Experiments for inducing sexual excitement by application of sinusoidal
magnetic fields have been performed using both topical and systemic field
application. Topical application of a sinusoidal multipole magnetic field
of order 6 to the lower lumbar region, with maximum field amplitude of
about 1 nanotesla, usually causes an erection after about 13 minutes
exposure, and the erection can be maintained as long as an hour. Effective
frequencies depend on physiolgical conditions, but a typical effective
frequency is 0.62 Hz.
Systemic application of an approximately uniform sinusoidal magnetic field
at a frequency of 0.55 Hz and an amplitude of 2.3 nanotesla results in
wooziness after about 2 hours exposure; sexual excitement sets in about 1
hour later. The sinusoidal magnetic field for this experiment was obtained
simply by using a 33 rpm phonograph turntable which carries two permanent
magnets with a total magnet moment of 6.5 Am.sup.2 ; the distance to the
subject was 10.4 m. Although the use of the 33 rpm turntable is
convenient, the frequency of 0.55 Hz is not optimum for excitation of the
1/2 Hz sensory resonance. This explains the long exposure times needed to
obtain a physiological response. Other experiments with systemic
application of magnetic fields, albeit with slightly greater
nonuniformity, have given results that are similar to those obtained with
topical applications of sharply localized fields.
The finding that excitation of the 1/2 Hz sensory resonance results in
different effects depending on the precise frequency near 1/2 Hz used
shows that the resonance has fine structure. However, all the effects
observed, i.e., ptosis of the eyelids, relaxation, sleepiness, a "knot" in
the stomach, a soft warm feeling in the stomach, a tonic smile, sudden
loose stool, and sexual excitement, involve the autonomic nervous system
in one way or the other. Moreover, the frequencies for which the different
effects are observed all lie close together near 1/2 Hz. It thus appears
that the separate resonances in the fine structure involve the same neural
and endocrine mechanism. The resonance phenomena, including their
physiological consequences, will therefore be collectively referred to as
"the 1/2 Hz sensory resonance".
The novel experiments and discoveries discussed above form the basis of the
present invention, in which a time-varying magnetic field, with certain
restrictions on the spectral power density and field strength, is applied
for the purpose of influencing a subject's nervous system, by way of the
1/2 Hz sensory resonance. The spectral restriction entails limiting the
spectral power density at frequencies in excess of 2 Hz to at least 20 dB
below the spectral maximum, and requiring the spectral function maximum to
lie in the frequency range 0.1 to 1 Hz. The spectral restriction is
imposed for the purpose of avoiding both the risk of kindling and a harsh
feeling, while it allows excitation of the 1/2 Hz sensory resonance,
either by tuning or by choosing an appropriate temporal structure of the
time variation of the field, such as a slightly chaotic frequency
schedule. The peak-to-peak field strength of the time-varying magnetic
field is restricted to the range 10 femtotesla to 100 nanotesla. For field
strengths in this range, the evoked signal input to the brain has a
signal-to-noise ratio which is small enough to not get checked by
nuisance-guarding neural circuitry, while it is still large enough to
cause long-term excitation of the resonant circuitry involved in the 1/2
Hz sensory resonance.
The characteristic time for the temporal behavior of the ptosis frequency,
such as the initial frequency drift discussed above, is of the order of
several minutes. This suggests that the 1/2 Hz resonance is modulated by a
process, the rate of which is controlled by bulk substance release or
uptake and perhaps a subsequent diffusion; candidates for the substance
are neurotransmitters, second messengers, and hormones. The process
whereby the ptosis frequency is influenced by the bulk substance release
or uptake is here called chemical modulation of the resonance. It is
expected that the substance concentration perturbations have other,
"extended", physiological effects as well. For instance, pathological
oscillatory activity of neural circuits, such as occurring in tremors and
seizures, is influenced by the chemical milieu of the neural circuits
involved. So are emotional disorders such as depression, mania, anxiety,
and phobia. Hence, the manipulation of the autonomic nervous system by
means of imposed oscillatory magnetic fields arranged to exite the 1/2 Hz
sensory resonance may afford, through extended chemical modulation, some
measure of control of these disorders, and of tremors and seizures as
well. It is postulated here that such control is possible. The control, if
administered properly, may provide a treatment of the disorders, through
conditioning and other plastic modifications of neural circuit parameters.
The invention may be used to prevent elileptic seizures by switching on the
magnetic stimulation when a seizure precursor or aura is felt by the
patient. A somewhat similar use is seen for the prevention of panic
attacks. The excitation of the 1/2 Hz sensory resonance by a time-varying
magnetic field can also be used as a modality for control and treatment of
emotional disorders, through its influence on the endocrine system!.
A preferred embodiment of the invention is shown in FIG. 1, where a voltage
generator 1, labeled as "GEN", is connected through a thin coaxial cable 2
to a coil assembly 3; the latter is placed some distance beneath the
subject 4 near the body region selected for topical application. The
frequency of the voltage generator 1 can be manually adjusted with the
tuning control 5, so that by manual scanning a frequency can be found at
which the 1/2 Hz sensory resonance is excited. Upon being energized by the
generator 1, the coil assembly 3 induces a magnetic field which at large
distances is a multipole field with field lines 6. The voltage generator
must be designed such that the output complies with the spectral
restrictions discussed above; this can easily be done by those skilled in
the art. The coil 3 can be conveniently placed under the mattress of a
bed. As an alternative to manual tuning, the time-varying voltage output
of the generator can be controlled automatically by a processor such as
the Basic Stamp 5!; the processor is programmed to administer a suitable
frequency schedule and on/off times. The setup of FIG. 1 has been employed
in the insomnia therapy experiments and the sexual arousal experiments
discussed.
For topical magnetic field applications, such as illustrated by FIG. 1, it
is important to have a sharply localized magnetic field, either to avoid
unwanted exposure of body regions away from the region of application, or
to decrease adaption, as discussed above. A planar coil assembly suitable
for the induction of such a sharply-localized magnetic field is shown in
FIG. 2. The assembly consists of four coils, referred to as 7, 8, 9, and
10, with alternating winding directions. The series assembly of coils is
connected to the coaxial feed cable 2. The coils 7-10 are mounted on an
adhesive sheet 11 of insulating material, and the assembly is covered by
adhesive tape. The coil diameters are proportional to 1, .sqroot.2,
.sqroot.3, 2, and the number of windings are respectively proportional to
4, -6, 4, -1, where positive numbers indicate clockwise windings, and
negative numbers indicate counterclockwise windings. For clarity, the
connecting wires between coils are shown as running at some distance from
each other, but these wires should actually be laid very close together,
in order that their induced magnetic fields cancel each other as much as
possible. With this understanding, the coil assembly of FIG. 2 can be
shown to induce at large distances r a magnetic potential
.PSI.=(630 .mu.N.sub.4 I/b 7)(R.sub.1 /r).sup.8 P.sub.7 (cos.theta.), (1)
where .mu.(=4.pi..times.10.sup.-7 H/m for free space) is the permeability,
N.sub.4 the number of windings of the fourth coil, I the current through
the coil assembly, R.sub.1 the radius of the first coil, P.sub.7 the
Legendre polynomial of degree 7, and (r,.theta.,.phi.) the polar
coordinate system centered at the coil center, with the direction
.theta.=0 taken along the coil axis 6!. From (1) the magnetic field B can
be calculated as
B=-grad.PSI.. (2)
From (1) and (2), one has for the coil of FIG. 2, with R.sub.1 =2 cm, and
N.sub.4 =2, at a point on the coil axis a large distance z from the coil
plane, for z/R.sub.1 >>1, the approximation
B=4.63.times.10.sup.-17 I/z.sup.9 tesla, (3)
where the current I is in ampere, and the distance z is in meters. Eq. (3)
shows that the far magnetic field falls off as the inverse ninth power of
distance, so that the field is sharply localized. For a current of 0.3 mA,
at a distance of 10 cm from the coil, Eq. (3) gives B=13.9 pT, which is
sufficient for a physiological effect when properly tuned; at 30 cm
distance the field is 0.7 fT, too small to have physiological influence.
Coils for induction of localized and nonuniform magnetic fields may be
designed with the following general procedure. The field at a point P on
the axis of a circular current loop of radius R is
B.sub.z =.mu.IR.sup.2 /2.rho..sup.3, (4)
where .mu. is the permeability, I the loop current, .rho..sup.2 =R.sup.2
+z.sup.2, and z is the distance from point P to the loop plane. Expanding
the factor 1/.rho..sup.3 as a power series in R.sup.2 /z.sup.2 results in
a multipole expansion of the field (4). Consider in a plane an assembly of
m concentric current loops with radii R.sub.j and currents I.sub.j, j=1 to
m. In the multipole expansion of the total magnetic field induced on the
axis of the current loop assembly, the m-1 lowest multipole contributions
can be made zero by choosing the loop radii and loop currents such as to
satisfy the equations
.SIGMA.R.sub.j.sup.2 I.sub.j =0, .SIGMA.R.sub.j.sup.4 I.sub.j =0, . . . ,
.SIGMA.R.sub.j.sup.2m-2 I.sub.j =0, (5)
where the summations extend from j=1 to j=m. Equations (5) form a Van der
Monde system 7!. Solutions provide radius ratios R.sub.j /R.sub.1, and
current ratios I.sub.j /I.sub.1 for j=2 to m. In practice the current
ratios are chosen as integers, so that the current loops can be
implemented as coils with integer numbers of windings, with the coils
placed in series with each other. A solution of this type is easily
constructed for any m, from a modification of the Pascal triangle for the
binomial coefficients. The modification entails starting each row of the
triangle with the row number, and completing the row by the well-known
Pascal triangle construction. One thus finds for the first row 1, for the
second row 2,1, for the third row 3,3,1, for the fourth row 4,6,4,1, etc.
For a assembly of m individual coils, the modified Pascal triangle must be
completed up to row m. The number of windings, N.sub.j, of the individual
coils j, j=1 to m, are then to be taken proportional to the sequence of
numbers in the mth row of the triangle, with alternating signs. The
squared radii, R.sub.j.sup.2, of the individual coils are to be taken
proportional to the index j. With I.sub.j =IN.sub.j, where I is the
current through the coil assembly, the R.sub.j and I.sub.j satisfy (5), as
can be verified by substitution, for any chosen value of m.
With equations (5) satisfied, the total magnetic field induced by the m
coils falls off as inverse distance raised to the power 1+2m, far away on
the axis of the coil assembly. Continuation of the field off the axis then
gives as dominant asymptotic field a multipole magnetic field of order 2m.
The procedure was followed in the design of the coil of FIG. 2, with m=4.
Coil assemblies that induce at large distance a multipole magnetic field
with a pole of order larger than 2 are here called multipole coils. It is
emphasized that the multipole coil design must be implemented acurately in
order that the lower-order multipole contributions cancel sufficiently to
provide at large distance the desired multipole field. The individual
coils of the multipole coils discussed above have circular shape, but
other shapes such as squares may be chosen as well. The far field would
then not be axisymmetric, and would thus involve spherical harmonics 6!.
For compliance with the MPRII guidelines for limitations of the exposure to
low frequency electromagnetic fields, a planar multipole coil which is to
be used directly on the skin may need to have distributed windings. FIG. 3
shows such a coil, which includes circular wire windings such as 12, with
connecting wires such as 13 and 14, that provide either a continuation of
the same winding sense to the next circular winding, such as connection
13, or else provide an oposite winding sense, such as connection 14. The
connecting wires have been drawn such as to show clearly the connections
to the current loops; in practice, all connecting wires should be laid
closely alongside the radial wire from the center conductor of the coaxial
cable 2 to the smallest winding, in order that the magnetic fields induced
by the currents in these wires cancel each other as closely as possible.
The magnet wire windings are sandwiched between two sheets of insulation
15. The serially connected windings are fed by the thin coaxial cable 2.
The radii R.sub.j of the windings have been chosen such that the coil
induces a magnetic field that asymptotically falls off as the distance to
the inverse 7th power, i.e., as the field of a multipole of order 6. This
is here achieved by having the radii of the circular windings respectively
proportional to the numbers in the sequence 0.8165, 0.8564, 1.0000,
1.0488, 1.1547, 1.2111, 1.2910, 1.3540, 1.4142, 1.4832, 1.5275, 1.6021,
1.7321, and 1.8166.
The distributed multipole coil of FIG. 3 was designed by distributing, in a
multipole coil with m=3, each of the coils with multiple windings to
several single windings, without violating Eq. (5). A planar circular
multiplet coil with m=3 has three concentric individual coils j, j=1 to 3,
with normalized squared radii, R.sub.j.sup.2 /R.sub.1.sup.2 equal to j,
and normalized winding numbers, N.sub.j /N.sub.3, respectively equal to
3,-3,1. For m=3, Eqs. (5) read
.SIGMA.R.sub.j.sup.2 I.sub.j =0, .SIGMA.R.sub.j.sup.4 I.sub.j =0, (6)
where the sums extend over j=1, 2, 3. A solution of Eqs. (6) is provided by
planar concentrated windings with squared radii, R.sub.j.sup.2
proportional to the sequence 1,2,3, and winding numbers N.sub.j
proportional to 3,-3,1, as given by the 3d row of the modified Pascal
triangle. The first coil, with j=1, is now spilt into 3 separate single
circular windings of squared radii 1-.DELTA., 1, and 1+.DELTA.. Likewise,
the second concentrated coil, with j=2, is split into 3 separate single
circular windings with squared radii 2-.DELTA., 2, and 2+.DELTA.. The
third concentrated coil, j=3, is left unchanged. One thus arrives at the
coil assembly with squared radii proportional to the sequence 1-.DELTA.,
1, 1+.DELTA., 2-.DELTA., 2, 2+.DELTA., 3, and with currents proportional
to 1, 1, 1, -1, -1, -1, 1. Substitution into Eqs. (6), with the sums
extending over j=1 to 7, shows these equations to be satisfied for any
value of .DELTA.. An equidistant sequence of squared radii is obtained for
.DELTA.=1/3, with the result that the R.sub.j.sup.2 are proportional to
the sequence
0.6667, 1.0000, 1.3333, 1.6667, 2.000, 2.3333, and 3.0000. (7)
Coil assemblies may be composed by taking linear combinations of
R.sub.j.sup.2 sequences; Eqs. (6) then remain valid for the composite coil
assembly. A linear combination of two identical sequences (7), with
coefficients 1 and 1.1, gives R.sub.j.sup.2, j=1 to 14, proportional to
the sequence 0.6667, 0.7333, 1.0000, 1.1000, 1.3333, 1.4667, 1.6667,
1.8337, 2.0000, 2.2000, 2.3333, 2.5663, 3.0000, and 3.3000. The
corresponding currents are 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, 1,
and 1. Taking square roots of the R.sub.j.sup.2 sequence gives the
circular current loop radii R.sub.j shown above and implemented in the
distributed multipole coil of FIG. 3.
The procedure may be generalized to design a distributed planar circular
multipole of any even order 2m. Each of the individual coils with multiple
windings is spread into N.sub.j separate single windings with squared
radii R.sub.jk.sup.2, k=1 to N.sub.j, proportional to an equispaced
sequence centered on R.sub.j.sup.2, and with spacing .DELTA..sub.j. The
spacings .DELTA..sub.j, j=1 to m-1, can be chosen such that Eqs. (5) are
satisfied and bunching of the individual windings is minimized. If
desired, linear combinations of the resulting coils can be constructed.
For m smaller than 5, the equations for s.sub.k.sup.2 are linear; for m 5
or 6, they are quadratic and can still be solved easily. For m larger than
6, the equations can be solved by numerical methods. In practice, one
rarely needs to go beyond m=4, since the multipole of order 8 gives
adequate localization of the induced magnetic field.
A simple near-sine wave generator which satisfies the spectral restrictions
of the invention is shown in FIG. 4. The battery powered generator is
built around two RC timers 16 and 17, and an operational amplifier 18.
Timer 17 (Intersil ICM7555) is hooked up for astable operation; it
produces a square wave voltage with a frequency determined by
potentiometer 19 and capacitor 20. The square wave voltage at output 21
drives the LED 22, and serves as the inverting input for the amplifier 18
(MAX480), after voltage division by potentiometer 23. The noninverting
input of amplifier 18 is connected to an intermediate voltage produced by
resistors 24 and 25. Automatic shutoff of the voltage that powers the
timer and the amplifier, at point 26, is provided by a second timer 16
(Intersil ICM7555), hooked up for monostable operation. The shutoff occurs
after a time interval determined by resistor 27 and capacitor 28. Timer 16
is powered by a 3 volt battery 29, controlled by a switch 30. The
amplifier 18 is hooked up as an integrator. Additional integration is
performed by the capacitor 31 and resistor 32. The resistor 33 limits the
output current to the terminals 34 that are connected to the coil assembly
by the coaxial cable 2.
Two problems are encountered when a sinusoidal magnetic field is used for
excitation of the sensory resonance near 1/2 Hz. After the resonance is
first established, the resonant frequency slowly drifts downward, so that
the voltage generator has to be retuned frequently in order that the
resonance be maintained. This manual tracking of the resonant frequency is
an inconvenience to the subject. The other problem encountered is an
adaption of the central nervous system to the signals evoked by the
magnetic field. The time to adaption depends on the strength of the FM
signals evoked by the oscillating magnetic field, as compared with the
relevant noise. For large signal-to-noise ratio (S/N), the evoked signal
is quickly recognized by the brain as an irrelevant nuisance, and the
evoked signals are blocked from further processing. For very small S/N no
effect is felt. There is an intermediate range of S/N for which the evoked
signals, although not recognized as a nuisance, are strong enough to
excite the sensory resonance. By continuity, one expects that there is an
optimum S/N for effective magnetic field application for purposes of
exciting the 1/2 Hz sensory resonance. It has been found however, that
repeated application at the optimum S/N still illicits a slow adaption.
The adaption can be circumvented by using topical application to different
body sites. There further is merit in using a magnetic field that is not
precisely sinusoidal, but has a weakly stochastic nature, with a narrow
power spectrum around the resonant frequency. A generator that produces
such a weakly stochastic nearly harmonic voltage is shown in FIG. 5. The
generator contains a dual timer 35 (Intersil ICM7556) that is hooked up
such as to produce a chaotic square wave at point 36. Both sections of the
dual timer 35 are hooked up for astable operation, with slightly different
RC times. The RC time of the first timer section is determined by the
resistor 37 and capacitor 38. The RC time of the second timer section
determined by the resistor 39 and the capacitor 40. The two timer sections
are coupled by connecting their outputs crosswise to the threshold pins,
via resistors 41 and 42, with capacitors 43 and 44 to ground. For a proper
range of component values, easily found by trial and error, the square
wave output of each of the timer sections is chaotic. The component values
can be adjusted experimentally to provide a chaotic output with acceptable
characteristics. An example for the chaotic output is shown in FIG. 6,
where the points plotted correspond to transitions (edges) of the square
wave. Abscissa 45 and ordinates 46 of a plotted point are time intervals
between consecutive transitions of the square wave output; for any
transition, the abscissa is the time to the preceding transition, and the
ordinate is the time to the nect transition. Starting with transition 47,
consecutive transitions are found by following the straight lines shown.
The transition times follow a pseudo random sequence, with some order
provided by the oval attractor. The results shown in FIG. 6 were derived
from the voltage measured at point 36 of the device of FIG. 5, with the
following component values: R.sub.37 =1.22 M.OMEGA., R.sub.39 =1.10
M.OMEGA., R.sub.41 =440 K.OMEGA., R.sub.42 =700 K.OMEGA., C.sub.38 =0.68
.mu.F, C.sub.40 =1.0 .mu.F, C.sub.43 =4.7 .mu.F, and C.sub.44 =4.7 .mu.F.
In the above list, R.sub.i is the resistance of component i in FIG. 5, and
C.sub.j is the capacitance of component j. The chaotic square wave at
point 36 is used, after voltage division by potentiometer 23, as input for
the micropower operational amplifier 18 (MAX480) hooked up as an
integrator. Additional integration is performed by the capacitor 31 and
resistor 32. The output current to the coil via the coaxial cable 2 is
limited by resistor 33.
FIG. 7 shows part of the spectral power density function (also called
"spectral density") of the voltage produced by the generator of FIG. 5,
with the component values mentioned. The spectral power density is shown
in dB below the maximum 48 which occurs at a frequency of 0.42 Hz. In
order to prevent kindling 4! and irritating the brain, the spectral
density should, for all frequencies in excess of 2 Hz, be more than 20 dB
below the spectral maximum. In FIG. 7, the -20 dB line is shown as 49.
The magnetic field for exciting the 1/2 Hz sensory resonance need not be
generated by currents in a coil; instead it may be provided by a permanent
magnet that is moved such as to cause dipole radiation. FIG. 8 shows such
an embodiment in the form of a aero-mechanical device for generating a
fluctuating magnetic field for inducing relaxation and sleep. The idea is
to rock a permanent magnet by means of a mechanical oscillator that is
aerodynamically excited by small air currents that are present at the
device. The magnet then induces a fluctuating magnetic field by virtue of
its rocking motion. The device of FIG. 8 includes a mechanical oscillator
in the form of a rocker comprised of a hard domed shell 50 to which is
fastened a permanent magnet 51 and a silk flower 52. The rocker rests upon
a nonferromagnetic thin hard shell 53, which for tuning purposes is domed
to an adjustable extent by a screw 54 and a pressure plate 55. Small
oscillations of the rocker are excited by aerodynamic forces that act on
the silk flower 52 by virtue of small air currents and drafts at the
location of the device. The screw 54 engages a nonferromagnetic plate 56,
which is fastened to the shell 53. The screw 54 is maintained in the base
plate 57. By turning the assembly of plate 56 and shell 53 with respect to
the base plate 57, the natural oscillation frequency of the rocker can be
tuned. The design of the device may be done as follows. Let R.sub.d and
R.sub.s be respectively the radii of curvature of the outer surface of
dome 50 and shell 53. Let point A, denoted as 58, be the center of
curvature of the dome surface, and let point C, denoted by 59, be the
center of mass of the rocker. The natural frequency of the rocker, for
small excursions, is readily found to be
##EQU1##
where g is the acceleration of gravity, .gamma. the distance between
points A and C divided by R.sub.d, .alpha. the ratio of R.sub.d to
R.sub.s, and .xi. is the square of the radius of inertia of the rocker
with respect to the center of mass 59, divided by the square of R.sub.d.
In (8), the terms proportional to (1-.gamma.) are due to the translations
of the center of mass that accompany the rocker rotations. Eq. (8) shows
how to design the device such that the natural frequency f is near 1/2 Hz.
The frequency can be tuned by adjusting the radius of curvature R.sub.s of
the shell, by the screw arrangement shown in FIG. 8; this changes the
ratio .alpha. in (8). The aerodynamic forces acting on the silk flower by
air drafts have a wide frequency spectrum determined by air velocity
fluctuations and the shedding frequency of vortices off the silk flower.
For a device with small damping, the rocker response favors frequencies
near the natural frequency, so that the power spectrum of the rocker
oscillation is dominated by frequencies near f of (8). The resulting small
stochastic oscillation of the permanent magnet causes a fluctuating
magnetic field that decreases as the inverse third power of distance to
the device. Measurements near a properly tuned device subject to typical
residential air currents show an rms magnetic field strength of 13/r.sup.3
pT at a distance r from the device. An rms magnetic field fluctuation of 1
pT, which is plenty for occurrence of physiological effects, will be
induced at a distance of 2.3 m.
Another embodiment in which a moving magnet is used to induce the
time-varying magnetic field that is to excite the 1/2 Hz sensory resonance
is a rotating magnet assembly. The magnet rotation is brought about by
coils that receive voltage pulses of appropriate phase. Because very large
magnetic moments are easily obtained with permanent magnets, this
embodiment lends itself for projection of near 1/2 Hz oscillating magnetic
fields over several hundred meters. In view of the possibility to remotely
induce drowsiness in subjects at such distances, the embodiment can be
used as a nonlethal weapon. A suitable arrangement is shown schematically
in FIG. 9. Two permanent magnets 60 are mounted on an iron spacer 61,
which is fastened to a shaft 62 that can rotate freely in bearings 63.
Coils 64 are mounted such as to cause the magnet assembly to engage in a
continuous rotation, when pulsed electric currents are passed through the
coils in properly phased manner. The currents are caused by a driver 65
connected to the coils by wires 66. The period of rotation of the magnet
assembly is determined by the pulse frequency of the driver, shown by the
display 67; the period can be changed by operating up and down buttons 68
and 69. The driver may include a control unit 70 to provide a chosen
schedule of activity times and frequencies. The driver and the control
unit can be readily designed around a processor such as the Basic Stamp
5!, by those skilled in the art. A compact and rugged device of this kind
can be delivered to enemy teritory by mortar or air drop. The rotating
magnet assembly will induce at a point P at a distance of r meters from
the device a periodic magnetic field with peak to peak strength
B=4 .mu.M/(4.pi.r.sup.3) tesla, (9)
where M is the magnetic moment of the magnet assembly in Am.sup.2. Eq.(9)
is valid for remote points P in or near the plane through the center of
the magnet assembly, perpendicular to the axis of rotation of the magnet
assembly. For a device 5 cm in overall diameter, the magnetic moment M can
easily be made as large as 13 Am.sup.2. A periodic magnetic field with
peak-to-peak strength of 0.19 pT, sufficient for causing drowsiness, is
then induced at a distance r=300 m from the device.
In some social settings it is important that the magnetic field stimulus
can be applied inconspicuously. A compact device for this purpose is shown
in FIG. 10, where an eye shadow case 71 with hinge 72 contains both the
voltage generator 1' and the coil 3'. The tuning control 5', the power
switch, monitoring LED, and 3 V Lithium coin-type battery are accessible
after opening the clam-type case. The case can be carried in a purse or
trousers pocket, and can be used for months on a single battery.
As noted above, human sensitivity to the very weak magnetic fields with a
frequency near 1/2 Hz is not understood at present. However, several
pieces of the puzzle can be clarified, as follows.
1) Localized topical application of the oscillatory magnetic field is
afforded by multipole coils which induce fields that fall off sharply with
distance. For instance, the coil assembly of FIG. 2 provides a magnetic
pole of order 8, so that the asymptotic field falls off as the inverse 9th
power of distance. This affords application of the magnetic field to small
regions of the body away from the head, while the magnetic field exposure
of the brain is entirely negligible. Hence, in these experiments the
physiological effect is not due to magnetic fields acting directly on the
brain; also, because of the field localization, the effects are not due to
transmission to the brain of directly-induced (i.e., nonphysiological)
electric currents by high-conductivity paths provided by blood vessels,
lymph vessels, and spinal fluid. Thus the physiological effects in these
cases are obtained strictly via somatosensory pathways, and it follows
that the weak oscillatory magnetic field with frequency near 1/2 Hz
directly affects certain somatosensory receptors. What kind of receptors
are these, and what is the mechanism of susceptibility? A direct static
response to the magnetic field itself is ruled out, since, unlike
honeybees 8!, man has no innate abilty to navigate by the earth's
magnetic field. What remains is the notion of sensory receptors responding
to the electric fields and eddy currents induced by the magnetic field
oscillations. Order-of-magnitude calculations show that these electric
fields and eddy currents are far too small to serve as a trigger for
neuronal firing; the only way in which receptors can be influenced by the
minute induced electric fields and currents is in a gradual manner, as in
frequency modulation of spontaneous stochastic firing. But that is
precisely the information coding employed by the receptor types involved
in the 1/2 Hz sensory resonance, discussed in the Background Section:
vestibular end organs, muscle spindles, Ruffini endings, and cutaneous
cold and warmth receptors; all these receptors use frequency coding of the
sensed information. Which of these receptors is most likely to be
sensitive to the electric fields and eddy currents induced by the magnetic
field oscillations? We will return to this question after considering
several other aspects of the problem.
2) Since the eddy currents induced by the oscillatory magnetic field are
proportional to the time derivative of the field, it is of interest to
investigate the physiological effect of the rise time of square wave
magnetic fields. Experiments show that the rise time does not affect the
magnitude of the physiological response, but only its quality; short rise
times give a harsh feeling that is absent for large rise times or
sinusoidal field variation. It thus appears that the eddy currents, or the
concomitant electric fields in the body, mainly affect the experienced
response through their integrals over time.
Two candidates for a mechanism with such behavior come to mind, long-term
charge accumulation at high-resistivity structures by eddy currents, and
excitation of resonant neural circuits by afferent signals. The first
mechanism would require charge relaxation times of the order of or larger
than the period of the oscillatory magnetic field, say, 2 seconds; this
condition is not satisfied in the tissues involved. The other mechanism
considered is the excitation of a harmonic oscillator by a forcing
function with a frequency near resonance. For small damping (high Q), the
oscillator may get excited, over several cycles, to appreciable
amplitudes, by coherently absorbing energy from "the forcing function".
For high Q, considerable amplitudes result even in the presence of noise,
if the forcing function contains a substantial Fourier component near the
resonant frequency. The system acts as a sharp bandpass filter followed by
an amplifier, much as the regenerative circuit of early radio. In case of
a square wave forcing function, the response of the system is not
influenced much by the rise time of a square wave, but is essentially
determined by the forcing function integral over a quarter cycle. This is
the sought-after response.
3) A physiological response occurs only for weak magnetic fields. More
precisely, the frequency modulation of neuronal firing evoked by the
imposed oscillatory magnetic field and presented to the brain by afferents
must lie in a range that is limited below by modulations that are so weak
as to be indiscernible from the noise, even by the exquisitely sensitive
neural resonant circuitry involved, while the range is limited from above
by modulations that are strong enough to be recognized by the brain as an
irrelevant nuisance, and are therefore blocked from higher processing. The
lower limit exists in every analog signal processor. That an upper limit
exists as well is shown by experiments which employ moderately strong
magnetic fields at the resonant frequency; no physiological response is
observed in these cases. Thus emerging is a model in which the weak
oscillatory magnetic field causes a frequency modulation in the firing of
somatosensory receptors, so weak as to be burried in the noise; the faint
FM signal causes resonance in a high-Q neural circuit, if the field
frequency is near the resonant frequency of the circuit. The
signal-to-noise ratio of the frequency modulation is so small as to not
arouse a nuisance-blocking action by guard circuits.
4) The direct, i.e., non-physiological, effect of the imposed oscillatory
magnetic field can be described as follows. Eddy currents are induced in
the body by the electric field that results from oscillating magnetic
fluxes and also from polarization charges that accumulate on the body
surface and high-resistivity membranes. Charge concentrations in tissue
relax with a time constant
t.sub.c =.epsilon./.sigma., (10)
where .epsilon. is the permittivity and .sigma. is the conductivity of the
tissue. In biological tissue, the charge relaxation time t.sub.c is very
much shorter than the oscillation period of our magnetic field. Hence,
polarization charges that accumulate at the boundaries of high-resistivity
regions, such as membranes and skin surfaces, may be considered to be in
quasi-steady state, i.e., they are essentially in equilibrium. It follows
that these surface charge distributions are such that the total electric
field component normal to the surface vanishes; the eddy current at the
surface then flows tangentially, as required by the steady state of the
surface charge density. Thermal motion smears the surface charge into a
thin layer with thickness of the order of the Debye length 9!. In the
Debye layer, the perturbed ion concentrations provide a local pH
perturbation. Such local pH perturbations have an effect on the folding of
certain proteins through the interplay of hydrophobic molecular groups and
pentagonal water 10!. Such folding is expected to play an important role
in mechanoreceptors such as vestibular hair cells and muscle spindles. One
may expect that the sensitive pH dependence of the folding makes these
mechanoreceptors susceptible to weak imposed electric fields. Such
susceptibility, with great sensitivity, has indeed been observed by
Terzuolo and Bullock 11! for the nonadapting stretch receptor of
Crustacea, nearly 4 decades ago. A similar sensitivity to electric fields
and currents may be expected for vestibular hair cells. Such sensitivity
is postulated here.
5) Another consideration points to the same receptors. Some aquatic animals
have an exquisite sensitivity to external electric fields 12,13!. For
example, it has been shown that dogfish, when in a drowsy state, can
respond by eyelid movements (ptosis|) to a uniform electric field of 10
microvolt per meter, switched on and off with a frequency of 5 Hz 14,15!.
An even greater sensitivity, down to 1 microvolt per meter, has been
observed by monitoring heart rates 16,17!. It is noted in passing that
both the ptosis and the heart rate response involve the autonomic nervous
system of the fish. The pertinent sensory systems involve magnification of
the external electric field by high-conductivity paths in a
high-restitivity surround (by the Ampullae of Lorenzini 14!), specialized
receptors, and dedicated neural circuitry. The receptor sensitivity
appears to be comparable to that of our finest, the vestibular hair cells.
6) Looking, in man, for structures that provide a function similar to the
electric field magnification discussed under 5), two structures stand out:
muscle spindles and the semicircular canals of the vestibular organ.
Afferent endings of muscle spindles form spirals around intrafusal fibers
4!, and therefore provide a coil along which the emf due to oscillating
magnetic flux is integrated. The semicircular vestibular canals are filled
with endolymph 4!, which has high electric conductivity; hence,
comparatively large eddy currents are induced by the magnetic flux changes
through the area encircled by the semicircular canal. As a result, nearly
all of the emf induced along the canal is presented across the cupula that
holds the vestibular hair cells. It follows that the resulting local pH
perturbations at the receptors are magnified as a result of the special
structures involved.
In view of the considerations 1) to 6), it appears that likely candidates
for receptors which respond to the small electric fields and eddy currents
induced by the magnetic field oscillations involved in the experiments
discussed are the vestibular end organ and muscle spindles. It is here
postulated that these receptors do indeed respond to the oscillatory
magnetic field by slight frequency modulation of their spontaneous firing.
The invention is not limited by the embodiments shown in the drawings and
described in the description, which are given by way of example and not of
limitation, but only in accordance with the scope of the appended claims.
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* * * * *