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Toward quantification of athetotic movements by frequency spectrum analysis
,
EMcbus
Vol. 18. No. I. pp 71-‘6.
ca?l-9290
19135
85 13.00 4. al
% 1985 Pcrgamon Prcs Ltd.
Primed I” Great Bnum
TOWARD
QUANTIFICATION OF ATHETOTIC MOVEMENTS BY FREQUENCY SPECTRUM ANALYSIS SAEED
NIKU
California Polytechnic State University, San Luis Obispo, U. S. A. and JERALD M. HENDERSON University of California, i)avis. U. S. A. Abstract-The frequency spectrum of the elbow movements of one normal subject and six handicapped subjects were obtained in order to investigate the possibility of using this technique in quantifying athetosis. The frequency spectrum technique appears to be useful but data from more subjects must be obtained and specific details regarding scaling need to be investigated.
results show its usefulness in determining the effect of drug therapy in controlling involuntary movements. Neilson (1974a) has listed a number of studies attempting to measure athetosis and trying to describe it. In these studies, cinematography, accelerometers and electromyographic signals (EMGs) have been used as well as other techniques to measure athetosis and different kinds of tremors. For instance, Nielson (1974b) has recorded intention tremor on tape, has filtered the data and integrated it in order to quantify tremors. This is a useful method for quantifying tremors since the frequencies of tremors are distinctly different from the frequencies of normal movements of an arm. Neilson (1974a) tested cerebral palsied subjects in order to study athetosis. He performed freewheeling tests and visual tracking tests on his subjects, where in the latter the target was a line on a CRT screen being randomly moved by the experimenter. The target is claimed to have included all the frequencies of less than 1.5 Hz, and almost no frequency of more than 2 Hz. He measured the elbow angle and the EMG and IEMG (Integrated EMG) of the biceps muscle. He then used the frequency analysis method to find out that the maximum velocity and acceleration of arm movements in athetotic patients are about 30-SO”/0 of normal arms. This signifies that athetotic patients cannot move their arms as fast as a normal arm. He also found that an athetotic arm is underdamped, causing a rhythmical oscillation of the arm at about 0.3-0.6 Hz. Neilson (1974b), using the previously mentioned technique, also found that three separate components of involuntary activity can be recognized within the athetotic movements. First there is a continuous power spectrum representing irregular and random movements of up to 2-3 Hz. The power of the spectrum decreases as the frequency increases, reaching negligible values between 2-3 Hz. Second is the rhythmical low frequency movement of 0.3-0.6 Hz, shown by a predominant peak in the powerspectrum. Third is an
INTRODUCTIOK palsy is the general term applied to a group of permanently disabling symptoms resulting from damage to the developing brain that may occur before, during, or after birth and that results in the loss or impairment of control over voluntary muscles’ (Goldenson, 1978). It is a neuromuscular disease and generally non-progressive and its symptoms may change as physiological or emotional factors change. It is estimated that about 750,000 persons are affected by cerebral palsy in the U. S. One of the most important symptoms of cerebral play is athetosis. khetosis is an involuntary, unpredictable, random, and writhing movement of usually the upper limbs, with varying degrees of tension. Athetosis is the result of muscles being randomly contracted in time. Although athetosis occurs so frequently, it is usually described qualitatively and not quantitatively. There is no standard way to quantitatively measure it and the current techniques consist of subjective observations. Banham (1978) has made a checklist of fifty functions, where the observed performance of the cerebral palsy child is evaluated according to a three-level scale. Chyatte and Birdsong (1978) have designed a device to quantify athetosis by actually measuring the level of controlled motion assuming that the rest is uncontrolled and is athetosis. In this device, a timer and a pressure sensitive strip are combined to measure the uniformity of the movements of an arm, while the movements are being performed on the strip. No scales are given for comparison of the voluntary and involuntary motions. In order to measure the spasticactivities ofathetotic patients, Rapp and Carter (1966) used a polygraph, a device for measuring body changes in different emotional states. The polygraph was used to measure muscle activities, especially after drug treatment. The ‘Cerebral
Received Augur
1983; in recised/orm
I1 June 1984.
71
72
SEED
NIKU
and
JERALDM. HESDERSON
athetotic action tremor of 1.M Hz, caused by asynchronous contractions of antagonistic muscle groups. The purpose of this incestigation was to study the athetotic movements of arms and the possibility of using the frequency analysis technique to quantify athetosis by measuring the power level of distinct frequencies (Niku, 1982). EXPERIMENTAL
APPROACH
Seven subjects were tested. One was normal, five were cerebral palsied of different severities, and one was brain damaged in an accident. The experimental investigation consisted of recording freewheeling and visual tracking movements of the subjects’ arms. The movements were sensed by a potentiometer mounted on a brace which was worn by the subjects. In visual tracking tests, the subjects followed a motion pattern generator, generating sinusoidal motions of predetermined frequencies and amplitudes. The velocities of the movements were obtained by an electronic differentiator, and some tests were recorded on tape as well. Two braces were used for recording the motions-a rigid brace, and a flexible brace. The rigid brace consisted of an upper arm portion and a counterbalanced lower arm portion (Fig. la). The upper arm was connected to a frame, which in turn was connected to a base on an adjustable table. The lower portion rotated about the upper portion on a ball-bearing, thus allowing rotation about the elbow. Adjustable cuffs were used to attach the arm. The shaft was connected to a linear, single turn, conductive plastic potentiometer which as a goniometer could measure the position of the arm. The brace weighed 90 g without cuffs and 300 g with all the attachments.
TWO identical flexible braces were made of nylon strips connected to a potentiometer. Each brace weighed 120 g. These braces were not attached to any frame and thus would not restrict shoulder movements but still would only record the relative movements of the lower arm about the elbow joint (Fig. lb). The target for visual tracking tests was the extended rocker arm of an electromechanical four-link mechanism capable of producing approximate sinusoidal motions of any frequency between 0 and 120 cpm with varying amplitudes of O-80”. The target’s position was recorded via another goniometer connected to the rocker arm’s shaft. The target was mounted on the support stand next to the arm brace. Thus, the target’s movements could be easily seen and followed by the subjects. Each subject was asked to sit in an upright position either on a chair or in the subject’s wheelchair next to the adjustable table on which the experimental brace and the target were mounted. The table’s height was adjusted so that the elbow axis would align with the brace shaft. The arm was strapped to the brace so that it could move most comfortably in the sagittal or frontal plane, but firm enough to reduce backlash. The subjects were instructed to express any discomfort. For freewheeling, subjects were asked to move their arm as fast as they possibly could. The lower arm was initially horizontal (0’). Even though the subjects were not asked to maintain theamplitude oftheir freewheeling at any specific value, they usually moved their arm for about 80” total. After some preliminary training, the movements were recorded on tape for 60 s or more until the subjects expressed fatigue. The data gathering would then resume after a period of rest. For visual tracking tests, subjects were asked to follow the target arm of the motion pattern generator
Fig. 1. The experimental braces.
Toward
quantification
a)
of athetotic
73
movements
Typical Tracking Test
10 Hz
0.75
g.“’
10 Hz Subject
b)
The
Frequency
Spectrum
of !he Tracking
Test.
1 Set -_I
c)
Freewheeling
Flex.
Output.
0.95
f
IJ! /., d)
The
Frequency
Spectrum
10Hz
of the
Freewheeling
Fig. 2. The normal
subject.
p---
Test.
a) Typical
0.425
Tracking
Test.
0.85 1.275
/
10 Hz Target
0.425 0.6 0.8
10 Hz
A Subject b) The Frequency Spectrum of the Tracking
r Y) .Z 3~ jj ‘Z z
Test
1 Set 0.5
0.375 0.175:
10 Hz c) Typical
Freewheeling
Output and its Frequency Spectrum.
, 0.25
d) Second Set of Freewheelrng
Output and its Frequency
Fig. 3. An athetotic subject. 74
SPeCtrur.
4
I--
Toward
quantification
of athetoric
as closely as they could. The frequency of the target was different for different tests, but was always less than the frequency of freewheeling for that subject. The movements were recorded on tape for l-3 min until the subject was tired. The test was then repeated after a period of rest. The recorded data was then analyzed by a fast Fourier transform (FFT) analyzer. The objective of this analysis was to find any possible harmonic or nonharmonic peaks in the frequency content of the motions. Depending on the length of the data, a few spectrums would be calculated for several time intervals and then averaged automatically to obtain the best possible results. The visual tracking data was analyzed simultaneously with the target’s data using the dual channel capability of the FFT analyzer. The output was then plotted on an X-Y recorder. D!SCUSSION
OF RESULTS
Figure 2 shows the results of the freewheeling and tracking tests of the normal subject (male, 17 yr old) to be compared with cerebral palsied subjects. Arbitrary units can be used on the ordinate of the frequency spectrum plots since the relative heights of peaks due to athetosis compared with a peak corresponding to a normal motion being followed is the indication of athetosis.
75
movements
Figure 3 shows the results of a severely athetotic subject (female. 13 yr old, in wheelchair, spastic. athetotic, speechless). The involuntary motions are evident both in the movements and the frequency content plots. For the tracking test in addition to the peak frequency of 0.425 Hz, which is the basic frequency of the movement, there are some other short but detectable peaks of 0.35,0.6 and 0.8 Hz which make the target and subject plots different. The two freewheeling motions are of0.25 and 0.5 Hz frequencies. The higher frequency was performed first, and since the motion was so erratic the subject was asked to repeat it again slower (Fig. 3 c and d). For this second case, there was better control of the arm and the movement was improved. The spectrum of the faster freewheeling movement shows three separate peaks of 0.375, 0.5 and 0.8 Hz, and a continuous band of frequencies up to about 3 Hz. The slower movement, though, does not possess the same range of frequencies and mostly shows the basic frequency and its harmonics. This subject’s arm movements were also recorded while she performed some routine daily tasks such as brushing her hair, typing on a keyboard, using a communication board, and eating, as well as relaxing her arm and holding her arm at a certain position. Figure 4 shows the frequency content as she held her arm stationary. Athetosis was evident by obseming the subject directly as well as studying the frequency
tiiiiiiiiiiiiiiiiiiiiiiiiiirl a)
Relaxed
Arm.
1 Set
--I
10 Hz b) Arm Held
Fig.
Stationary
4. Stationary
and its Frequency
Spectrum
arm
subject.
for athetotic
I----
76
SAEED
NIKU and
JERALD
M. HENDERSON
in their performance as was evident in their recorded motions (Niku, 1982). This difference and its severity can also be detected in the frequency spectrums, both in freewheeling and visual tracking tests. Although there was much observable athetosis in the routine daily motions of the severely athetotic subject previously discussed, it was not evident in the frequency contents of those specific motions. This is due to the nature of athetosis being a random type of motion which gets lost in the voluntary motion. In visual tracking and freewheeling tests, though, the desired motions are repetitive. This results in the arm being in
Fig. 5. Comparison of frequency spectrums of the same strip of data with different starting points.
spectrum. Because of its simplicity, having a subject hold an arm steady and obtaining the frequency spectrum of involuntary motions might prove to be a useful clinical technique. Similar results were obtained from the other subjects depending on the severity of their athetosis. In order to determine the time dependency of the frequency content of each movement, the data were analyzed repeatedly, each time using a different starting point but always with the same time length of data. Figure 5 shows the difference between two sets of frequency contents of the same data with different starting points. Although the peak frequencies in the spectrums are similar, the amplitudes are different. CONCLUSIONS
The sufficient difference between the frequency contents of the motions of the normal subject and the cerebral palsied subjects suggest that the frequency analysis technique can be used to quantify the severity of athetotic motions. One subject, for example, had much less observable athetosis in her motions compared to another, and there was a significant difference
similar geometric states repeatedly. increasing the possibility of repeated frequencies in the athetotic involuntary motions. As a result, the severity of the athetotic motion becomes more significant in the spectrum and can be detected by comparing the heights of frequency peaks. In order to successfully quantify athetosis, a large number of subjects with a wide range of severity should be tested, and the frequency contents of their motions statistically related to clinical measurements. Then a universal method might be established to quantify the severity of athetotic motions. REFERENCES
Banham, K. M. (1978) Measuring functional motor rehabilitation of cerebral palsied infants and young children. Rehohil. Lit. 39. 11l-l 15. Chyatte, S. B. and Birdsong, J. H. (1978) A device to quantify athetosis. Am. J. occup. 7her. 26, 30-31. Goldenson, R. (Ed.) (1978) Disabilir) anal Rehabilirarion Handbook. McGraw-Hill, New York. Neilson, P. D. (1974a) Voluntary control ofarm movement in athetotic patients. 1. Neural. Neurosurg. PsJchia[. 37, 162-170. Neilson, P. D. (1974b) Measurement of involuntary arm movement in athetotic patients. J. Seurol. Neurosury. Psychiat. 37, 171-177. Niku, S. (1982) Preliminary study of the design criteria for suppressing athetotic arm movements, Ph. D. Dissertation, University of California, Davis. Rapp, S. and Carter C. H. (1966) Use of a polygraph to measure spastic activity in athetoid patients. J. New Druys, 49-54.
EMcbus
Vol. 18. No. I. pp 71-‘6.
ca?l-9290
19135
85 13.00 4. al
% 1985 Pcrgamon Prcs Ltd.
Primed I” Great Bnum
TOWARD
QUANTIFICATION OF ATHETOTIC MOVEMENTS BY FREQUENCY SPECTRUM ANALYSIS SAEED
NIKU
California Polytechnic State University, San Luis Obispo, U. S. A. and JERALD M. HENDERSON University of California, i)avis. U. S. A. Abstract-The frequency spectrum of the elbow movements of one normal subject and six handicapped subjects were obtained in order to investigate the possibility of using this technique in quantifying athetosis. The frequency spectrum technique appears to be useful but data from more subjects must be obtained and specific details regarding scaling need to be investigated.
results show its usefulness in determining the effect of drug therapy in controlling involuntary movements. Neilson (1974a) has listed a number of studies attempting to measure athetosis and trying to describe it. In these studies, cinematography, accelerometers and electromyographic signals (EMGs) have been used as well as other techniques to measure athetosis and different kinds of tremors. For instance, Nielson (1974b) has recorded intention tremor on tape, has filtered the data and integrated it in order to quantify tremors. This is a useful method for quantifying tremors since the frequencies of tremors are distinctly different from the frequencies of normal movements of an arm. Neilson (1974a) tested cerebral palsied subjects in order to study athetosis. He performed freewheeling tests and visual tracking tests on his subjects, where in the latter the target was a line on a CRT screen being randomly moved by the experimenter. The target is claimed to have included all the frequencies of less than 1.5 Hz, and almost no frequency of more than 2 Hz. He measured the elbow angle and the EMG and IEMG (Integrated EMG) of the biceps muscle. He then used the frequency analysis method to find out that the maximum velocity and acceleration of arm movements in athetotic patients are about 30-SO”/0 of normal arms. This signifies that athetotic patients cannot move their arms as fast as a normal arm. He also found that an athetotic arm is underdamped, causing a rhythmical oscillation of the arm at about 0.3-0.6 Hz. Neilson (1974b), using the previously mentioned technique, also found that three separate components of involuntary activity can be recognized within the athetotic movements. First there is a continuous power spectrum representing irregular and random movements of up to 2-3 Hz. The power of the spectrum decreases as the frequency increases, reaching negligible values between 2-3 Hz. Second is the rhythmical low frequency movement of 0.3-0.6 Hz, shown by a predominant peak in the powerspectrum. Third is an
INTRODUCTIOK palsy is the general term applied to a group of permanently disabling symptoms resulting from damage to the developing brain that may occur before, during, or after birth and that results in the loss or impairment of control over voluntary muscles’ (Goldenson, 1978). It is a neuromuscular disease and generally non-progressive and its symptoms may change as physiological or emotional factors change. It is estimated that about 750,000 persons are affected by cerebral palsy in the U. S. One of the most important symptoms of cerebral play is athetosis. khetosis is an involuntary, unpredictable, random, and writhing movement of usually the upper limbs, with varying degrees of tension. Athetosis is the result of muscles being randomly contracted in time. Although athetosis occurs so frequently, it is usually described qualitatively and not quantitatively. There is no standard way to quantitatively measure it and the current techniques consist of subjective observations. Banham (1978) has made a checklist of fifty functions, where the observed performance of the cerebral palsy child is evaluated according to a three-level scale. Chyatte and Birdsong (1978) have designed a device to quantify athetosis by actually measuring the level of controlled motion assuming that the rest is uncontrolled and is athetosis. In this device, a timer and a pressure sensitive strip are combined to measure the uniformity of the movements of an arm, while the movements are being performed on the strip. No scales are given for comparison of the voluntary and involuntary motions. In order to measure the spasticactivities ofathetotic patients, Rapp and Carter (1966) used a polygraph, a device for measuring body changes in different emotional states. The polygraph was used to measure muscle activities, especially after drug treatment. The ‘Cerebral
Received Augur
1983; in recised/orm
I1 June 1984.
71
72
SEED
NIKU
and
JERALDM. HESDERSON
athetotic action tremor of 1.M Hz, caused by asynchronous contractions of antagonistic muscle groups. The purpose of this incestigation was to study the athetotic movements of arms and the possibility of using the frequency analysis technique to quantify athetosis by measuring the power level of distinct frequencies (Niku, 1982). EXPERIMENTAL
APPROACH
Seven subjects were tested. One was normal, five were cerebral palsied of different severities, and one was brain damaged in an accident. The experimental investigation consisted of recording freewheeling and visual tracking movements of the subjects’ arms. The movements were sensed by a potentiometer mounted on a brace which was worn by the subjects. In visual tracking tests, the subjects followed a motion pattern generator, generating sinusoidal motions of predetermined frequencies and amplitudes. The velocities of the movements were obtained by an electronic differentiator, and some tests were recorded on tape as well. Two braces were used for recording the motions-a rigid brace, and a flexible brace. The rigid brace consisted of an upper arm portion and a counterbalanced lower arm portion (Fig. la). The upper arm was connected to a frame, which in turn was connected to a base on an adjustable table. The lower portion rotated about the upper portion on a ball-bearing, thus allowing rotation about the elbow. Adjustable cuffs were used to attach the arm. The shaft was connected to a linear, single turn, conductive plastic potentiometer which as a goniometer could measure the position of the arm. The brace weighed 90 g without cuffs and 300 g with all the attachments.
TWO identical flexible braces were made of nylon strips connected to a potentiometer. Each brace weighed 120 g. These braces were not attached to any frame and thus would not restrict shoulder movements but still would only record the relative movements of the lower arm about the elbow joint (Fig. lb). The target for visual tracking tests was the extended rocker arm of an electromechanical four-link mechanism capable of producing approximate sinusoidal motions of any frequency between 0 and 120 cpm with varying amplitudes of O-80”. The target’s position was recorded via another goniometer connected to the rocker arm’s shaft. The target was mounted on the support stand next to the arm brace. Thus, the target’s movements could be easily seen and followed by the subjects. Each subject was asked to sit in an upright position either on a chair or in the subject’s wheelchair next to the adjustable table on which the experimental brace and the target were mounted. The table’s height was adjusted so that the elbow axis would align with the brace shaft. The arm was strapped to the brace so that it could move most comfortably in the sagittal or frontal plane, but firm enough to reduce backlash. The subjects were instructed to express any discomfort. For freewheeling, subjects were asked to move their arm as fast as they possibly could. The lower arm was initially horizontal (0’). Even though the subjects were not asked to maintain theamplitude oftheir freewheeling at any specific value, they usually moved their arm for about 80” total. After some preliminary training, the movements were recorded on tape for 60 s or more until the subjects expressed fatigue. The data gathering would then resume after a period of rest. For visual tracking tests, subjects were asked to follow the target arm of the motion pattern generator
Fig. 1. The experimental braces.
Toward
quantification
a)
of athetotic
73
movements
Typical Tracking Test
10 Hz
0.75
g.“’
10 Hz Subject
b)
The
Frequency
Spectrum
of !he Tracking
Test.
1 Set -_I
c)
Freewheeling
Flex.
Output.
0.95
f
IJ! /., d)
The
Frequency
Spectrum
10Hz
of the
Freewheeling
Fig. 2. The normal
subject.
p---
Test.
a) Typical
0.425
Tracking
Test.
0.85 1.275
/
10 Hz Target
0.425 0.6 0.8
10 Hz
A Subject b) The Frequency Spectrum of the Tracking
r Y) .Z 3~ jj ‘Z z
Test
1 Set 0.5
0.375 0.175:
10 Hz c) Typical
Freewheeling
Output and its Frequency Spectrum.
, 0.25
d) Second Set of Freewheelrng
Output and its Frequency
Fig. 3. An athetotic subject. 74
SPeCtrur.
4
I--
Toward
quantification
of athetoric
as closely as they could. The frequency of the target was different for different tests, but was always less than the frequency of freewheeling for that subject. The movements were recorded on tape for l-3 min until the subject was tired. The test was then repeated after a period of rest. The recorded data was then analyzed by a fast Fourier transform (FFT) analyzer. The objective of this analysis was to find any possible harmonic or nonharmonic peaks in the frequency content of the motions. Depending on the length of the data, a few spectrums would be calculated for several time intervals and then averaged automatically to obtain the best possible results. The visual tracking data was analyzed simultaneously with the target’s data using the dual channel capability of the FFT analyzer. The output was then plotted on an X-Y recorder. D!SCUSSION
OF RESULTS
Figure 2 shows the results of the freewheeling and tracking tests of the normal subject (male, 17 yr old) to be compared with cerebral palsied subjects. Arbitrary units can be used on the ordinate of the frequency spectrum plots since the relative heights of peaks due to athetosis compared with a peak corresponding to a normal motion being followed is the indication of athetosis.
75
movements
Figure 3 shows the results of a severely athetotic subject (female. 13 yr old, in wheelchair, spastic. athetotic, speechless). The involuntary motions are evident both in the movements and the frequency content plots. For the tracking test in addition to the peak frequency of 0.425 Hz, which is the basic frequency of the movement, there are some other short but detectable peaks of 0.35,0.6 and 0.8 Hz which make the target and subject plots different. The two freewheeling motions are of0.25 and 0.5 Hz frequencies. The higher frequency was performed first, and since the motion was so erratic the subject was asked to repeat it again slower (Fig. 3 c and d). For this second case, there was better control of the arm and the movement was improved. The spectrum of the faster freewheeling movement shows three separate peaks of 0.375, 0.5 and 0.8 Hz, and a continuous band of frequencies up to about 3 Hz. The slower movement, though, does not possess the same range of frequencies and mostly shows the basic frequency and its harmonics. This subject’s arm movements were also recorded while she performed some routine daily tasks such as brushing her hair, typing on a keyboard, using a communication board, and eating, as well as relaxing her arm and holding her arm at a certain position. Figure 4 shows the frequency content as she held her arm stationary. Athetosis was evident by obseming the subject directly as well as studying the frequency
tiiiiiiiiiiiiiiiiiiiiiiiiiirl a)
Relaxed
Arm.
1 Set
--I
10 Hz b) Arm Held
Fig.
Stationary
4. Stationary
and its Frequency
Spectrum
arm
subject.
for athetotic
I----
76
SAEED
NIKU and
JERALD
M. HENDERSON
in their performance as was evident in their recorded motions (Niku, 1982). This difference and its severity can also be detected in the frequency spectrums, both in freewheeling and visual tracking tests. Although there was much observable athetosis in the routine daily motions of the severely athetotic subject previously discussed, it was not evident in the frequency contents of those specific motions. This is due to the nature of athetosis being a random type of motion which gets lost in the voluntary motion. In visual tracking and freewheeling tests, though, the desired motions are repetitive. This results in the arm being in
Fig. 5. Comparison of frequency spectrums of the same strip of data with different starting points.
spectrum. Because of its simplicity, having a subject hold an arm steady and obtaining the frequency spectrum of involuntary motions might prove to be a useful clinical technique. Similar results were obtained from the other subjects depending on the severity of their athetosis. In order to determine the time dependency of the frequency content of each movement, the data were analyzed repeatedly, each time using a different starting point but always with the same time length of data. Figure 5 shows the difference between two sets of frequency contents of the same data with different starting points. Although the peak frequencies in the spectrums are similar, the amplitudes are different. CONCLUSIONS
The sufficient difference between the frequency contents of the motions of the normal subject and the cerebral palsied subjects suggest that the frequency analysis technique can be used to quantify the severity of athetotic motions. One subject, for example, had much less observable athetosis in her motions compared to another, and there was a significant difference
similar geometric states repeatedly. increasing the possibility of repeated frequencies in the athetotic involuntary motions. As a result, the severity of the athetotic motion becomes more significant in the spectrum and can be detected by comparing the heights of frequency peaks. In order to successfully quantify athetosis, a large number of subjects with a wide range of severity should be tested, and the frequency contents of their motions statistically related to clinical measurements. Then a universal method might be established to quantify the severity of athetotic motions. REFERENCES
Banham, K. M. (1978) Measuring functional motor rehabilitation of cerebral palsied infants and young children. Rehohil. Lit. 39. 11l-l 15. Chyatte, S. B. and Birdsong, J. H. (1978) A device to quantify athetosis. Am. J. occup. 7her. 26, 30-31. Goldenson, R. (Ed.) (1978) Disabilir) anal Rehabilirarion Handbook. McGraw-Hill, New York. Neilson, P. D. (1974a) Voluntary control ofarm movement in athetotic patients. 1. Neural. Neurosurg. PsJchia[. 37, 162-170. Neilson, P. D. (1974b) Measurement of involuntary arm movement in athetotic patients. J. Seurol. Neurosury. Psychiat. 37, 171-177. Niku, S. (1982) Preliminary study of the design criteria for suppressing athetotic arm movements, Ph. D. Dissertation, University of California, Davis. Rapp, S. and Carter C. H. (1966) Use of a polygraph to measure spastic activity in athetoid patients. J. New Druys, 49-54.