Biomedical subjects

A Beuter

Publications and source records attributed to A Beuter.

At least 19 recordsLinked to original sources

PubMed2005

Sensorimotor mapping affects movement correction deficits in early Huntington's disease.

Huntington's disease (HD) is associated with early voluntary movement problems linked to striatal dysfunction. In pointing movements, HD increases the irregularity of the terminal part of movements, suggesting a dysfunction in error feedback control. We tested this hypothesis in movements requiring continuous feedback control. Patients in the early stages of HD and controls traced as fast and accurately as possible circles within a 5-mm annulus on a digitizing tablet when visual feedback of the hand and the circle was direct or indirect (through a monitor). Patients deviated more often from the annulus and showed larger corrections toward the circle than controls when using indirect visual feedback but not with direct visual feedback. When velocity requirements were removed, patients showed little change in these control problems. These results suggest that HD does not affect error feedback control in all movements and that the striatal contribution to voluntary movement is sensitive to sensorimotor mapping.

Adult↗

PubMed2004

Accelerometric measurement of involuntary movements during pallidal deep brain stimulation of patients with generalized dystonia.

Accelerometric activity during rest and posture was quantified in the upper dominant limb of 14 patients with primary or secondary dystonia and five healthy control subjects. Data were recorded before and after bilateral implantation of the stimulating electrodes in the Globus Pallidus internus. Clinical evaluation was based on the Burke-Marsden-Fahn's Dystonia Rating Scale (BMFDRS). For the patient group, I(t), the integral (i.e. area) of the acceleration power spectrum over the total frequency range (0.6-16 Hz) decreased as the clinical state of the patients improved following deep brain stimulation (p < 0.01) during rest and posture. Ten days after surgery, there were no I(t) differences between control subjects and patients (p > 0.05). A significant correlation was found between the global BMFDRS scores and I(t) for rest (p < 0.01) but not for posture. No significant correlation was found between I(t) and a partial BMFDRS score for the right arm for rest or posture. The integral I(t) provides a valid indicator of the motor activity generated by the arm of the patient but further analyses are needed to monitor patients' progress not only during their hospitalization but also after they are released from the hospital, and to understand why this measure does not correlate with partial BMFDRS scores.

Adolescent↗

PubMed2004

[Kinematic evaluation of dystonic syndromes in patients treated with deep brain stimulation].

INTRODUCTION: Quantification of motor functions of patients with dystonic syndromes treated by chronic high frequency stimulation of the internal globulus pallidus is a challenge. OBJECTIVE: Through a series of clinical examples this paper shows that kinematic analysis of movements in dystonic syndromes treated by deep brain stimulation (DBS) is a complement to clinical evaluation. In addition, it provides valuable information for early detection of improvement or impairment of movements associated with modifications of stimulation parameters. METHOD: Thirteen dystonic patients and eleven reference subjects completed three tests (i.e., rest: lying supine; posture: standing with arms held in front (at shoulder height); and alternative movements: bimanual finger-to-nose test). These tests were recorded with an electromagnetic system quantifying movement kinematics (position) in three-dimensional space. RESULTS: From the recorded data, several indices were developed and provided a quantitative evaluation of movements during each test. In addition, a clinical evaluation (BMFDRS) was also completed. No correlation between clinical and kinematic evaluations was found. CONCLUSION: It is shown that kinematic analysis is a useful complement of clinical evaluation and can assist clinicians in monitoring the evolution of movements in dystonic patients treated by DBS in a simple, reliable and valid fashion.

Adult↗

PubMed2002

[Characterization and discrimination of kinetic tremor in Parkinson's disease].

Kinetic tremor recorded with a laser system during a compensatory tracking task of the index finger was analyzed in 21 patients with PD whose tremor amplitude was between low and moderate, and 30 control subjects. Nine characteristics quantifying the tracking task and tremor including mean tracking error, reaction time, peakedness, harmonicity, median frequency, proportional power in the 3-4 Hz, 4-6 Hz and 7-12 Hz ranges, and power at 0.25 Hz, were applied to the processed signal. The discriminating power of each characteristic was evaluated using differences between group means (p values), maximum percentage discrimination, and number of outliers in the patient group using z-score and 96.7(th) percentile of the control group. All nine characteristics showed significant differences between means of the two groups using Welch-modified t-tests for unequal variances. The most discriminating characteristics reflected differences in the frequency distribution of the movement and did not correlate highly with postural tremor amplitude nor with clinical ratings of tremor. Discrimination methods classified correctly up to 66.7 p.cent of the patients. Combining representative information about proportional power during posture and tracking gave a much higher discrimination (90 p.cent) with respect to the 96.7th percentile of the control group. These results suggest that by combining information coming from postural and kinetic tremors it is possible to isolate a specific aspect of PD symptomatology which could be used to reevaluate the classic distinction made between the akineto-rigid and tremulous forms of PD independently of tremor amplitude.

Female↗

PubMed2000

Using time domain characteristics to discriminate physiologic and parkinsonian tremors.

Tremor amplitude and frequency do not always clearly differentiate subjects with particular pathologies from control subjects or from subjects with other pathologies, especially in early stages of a disease. For patients with early stages of Parkinson's disease (PD) the discriminative power of amplitude was compared with that of other time domain characteristics of tremor recordings that are probably not evident clinically. Postural tremor with and without visual feedback and rest tremor were recorded in both hands of a group of patients with Parkinson's disease (n = 21) and a group of healthy control subjects (n = 30) using displacement lasers. Velocity and acceleration data were derived from displacement data. Twelve time domain characteristics were calculated on each recording and the discriminating power of each was evaluated using the worse hand in each case. Postural tremor with no visual feedback separates the two groups of subjects most efficiently, especially in velocity and acceleration. Tremor in Parkinson's disease (in comparison to normal physiologic tremor) has a specific morphology, has a distinctive histogram, is more periodic, and contains indications of nonlinearity in the underlying dynamics. There may also be greater difference in amplitude between the two hands and time asymmetry in tremor of patients with PD. A series of finger flexions seems to enhance normal tremor but not tremor in PD and may thus aid in discrimination. Discrimination of tremor attributable to PD from normal physiologic tremor can be enhanced by measuring time domain characteristics subtler than amplitude, particularly when amplitude itself is not large. Tremor measurement should not be limited to acceleration data because some information is more visible in other variables.

Aged↗

PubMed2000

Physiological tremor: does handedness make a difference?

The purpose of this study was to quantify with precision the characteristics of normal physiological tremor in the dominant and nondominant hand of a group of right-handed females. Twenty-two right-handed females (aged 20 to 40) gave informed consent to participate. Manual dominance determined with a questionnaire had to be equal to, or above 90%, for subjects to be accepted in the study. While the subjects kept their eyes closed, tremor was recorded simultaneously in the two extended index fingers during 40 s. Preceding the recording of postural tremor there was a period during which the subjects were asked to relax (control condition); to exert a pressure with the two index fingers on two strain gauges (static condition); or to press on and off with both index fingers on two strain gauges (dynamic condition). Each condition was recorded twice with two helium neon velocity lasers. This procedure was repeated after permutation of the lasers, thus a total of twelve sweeps of data were recorded. Seven parameters were used to analyze the tremor signal including measures of harmonicity, median frequency, proportional power in the 7-12 Hz range, amplitude, waveform morphology, entropy, and nonlinearity. Significant differences between hands were found in three parameters (median frequency, power in 7-12 Hz and entropy) but not in tremor amplitude (RMS). In addition, significant differences were found in five out of seven characteristics between conditions. These results suggest that neuromotor activity preceding the recording of tremor has a significant influence on tremor characteristics and that some of these characteristics are significantly different between the right and left hand in right-handed females.

Adult↗

PubMed2000

Standardization of a neuromotor test battery: the CATSYS system.

Interindividual and intraindividual variability in neuromotor behaviors is expected and normal. Early changes in neuromotor behaviors associated with neurodegenerative disorders or neurotoxic effects are often subtle and fluctuating in their characteristics. Therefore, their detection at an early stage is particularly difficult without precise recording instruments. The CATSYS system developed by Danish Product Development (DPD) is a portable device recording four measures of neuromotor control including tremor, reaction time, hand coordination and postural sway. The aim of this study is to develop a set of normative data. One hundred and fifty healthy men and women were divided into five age groups: (1) 20 to 29 years (n=30); (2) 30 to 39 years (n=30); (3) 40 to 49 years (n=30); (4) 50 to 59 years (n=30); (5) 60 to 70 years (n=30). All participants were free of neurological deficits at the time of testing and they were tested individually for approximately 30 min. Hand coordination was measured with prono-supination and finger-tapping movements executed at constant and accelerated rhythms. Reaction time was assessed in both hands using a hand held switch activated by the thumb. Postural tremor was quantified in both hands during 24.6 sec. by asking the subject to hold a stylus horizontally at 10 cm in front of his/her navel. The stylus contained a biaxial accelerometer. Postural sway was tested by asking the subject to stand on a force platform for 75 sec. under four conditions: (1) eyes open; (2) eyes closed; (3) eyes open standing on a foam pad; and (4) eyes closed standing on a foam pad. ANOVAs and multiple comparison tests were performed and the results were examined taking into account age, gender and experimental condition effects.

Adult↗

PubMed1999

The measurement of tremor using a velocity transducer: comparison to simultaneous recordings using transducers of displacement, acceleration and muscle activity.

Precise kinematic measurements of tremor have historically been obtained using accelerometers. However, current technology permits precise measurements in velocity and displacement. The primary advantage of velocity recording is that only one step of integration or differentiation is required for either displacement or acceleration. A method is presented of measuring finger tremor using a laser system that transduces velocity precisely. Measurements of postural finger tremor thus obtained were compared to those simultaneously obtained from a laser system that transduces displacement, from an accelerometer and from surface electromyography (EMG) of the extensor digitorum communis. A range of amplitude and frequency content was obtained by testing control subjects and subjects with Parkinson's disease. The velocity transducer showed excellent correspondence of amplitude and frequency measurement with the displacement transducer. Measures of absolute and relative amplitude correlated well (r > or = 0.96 in amplitude measures in displacement, velocity and acceleration), and high coherence was found throughout the frequency range of interest. Measurements by the accelerometer generally showed poorer correspondence with those of the other instruments. EMG measurements showed good correspondence in some trials but poorer correspondence in others, attributed to the low level of muscle activity required in the task. Precise kinematic measurements appear to be highly sensitive to neuromotor impairment.

Acceleration↗

PubMed1999

Parkinsonian tremor and simplification in network dynamics.

We explore the behavior of richly connected inhibitory neural networks under parameter changes that correspond to weakening of synaptic efficacies between network units, and show that transitions from irregular to periodic dynamics are common in such systems. The weakening of these connections leads to a reduction in the number of units that effectively drive the dynamics and thus to simpler behavior. We hypothesize that the multiple interconnecting loops of the brain's motor circuitry, which involve many inhibitory connections, exhibit such transitions. Normal physiological tremor is irregular while other forms of tremor show more regular oscillations. Tremor in Parkinson's disease, for example, stems from weakened synaptic efficacies of dopaminergic neurons in the nigro-striatal pathway, as in our general model. The multiplicity of structures involved in the production of symptoms in Parkinson's disease and the reversibility of symptoms by pharmacological and surgical manipulation of connection parameters suggest that such a neural network model is appropriate. Furthermore, fixed points that can occur in the network models are suggestive of akinesia in Parkinson's disease. This model is consistent with the view that normal physiological systems can be regulated by robust and richly connected feedback networks with complex dynamics, and that loss of complexity in the feedback structure due to disease leads to more orderly behavior.

Humans↗

PubMed1999

Quantitative analysis of rapid pointing movements in Cree subjects exposed to mercury and in subjects with neurological deficits.

To quantify rapid and precise proximo-distal movements, we have developed a simple system (eurythmokinesimeter or EKM) which requires the subject to touch alternately the center of proximal and distal targets with a stylus. Ninety-six participants, including 30 controls subjects, 36 Cree subjects exposed to mercury, 21 subjects with Parkinson disease, 6 with presumed cerebellar deficit, and 3 with essential tremor, participated in the study. A total of nine measures, including precision, imprecision, contact duration, unsureness, tremor, transit time, irregularity, speed, and Fitts' constant, were calculated. Test-retest reliability was above 0.8 for most measures and above 0.9 for many measures. Correlations between measures and number of outliers with respect to the control group distribution for each measure were used to reduce the set of measures to five (i.e., precision, imprecision, tremor, Fitts' constant, and irregularity). An ANOVA on the three largest groups generated significant results for tremor, Fitts' constant, and irregularity between the Cree and the control subjects and on Fitts' constant and irregularity between the subjects with Parkinson's disease and the control subjects. Three subgroups of the same mean age composed of six subjects each were selected. One was composed of Cree subjects with the highest level of mercury exposure, another with Cree subjects having a low level of mercury exposure, and a third with control subjects. An ANOVA on these three groups revealed a significant difference between both groups of Cree subjects and the control group for Fitts' constant and irregularity. These preliminary results suggest that the EKM system is able to discriminate the performance of different groups of subjects.

Analysis of Variance↗

PubMed1999

Analysis of rapid alternating movements in Cree subjects exposed to methylmercury and in subjects with neurological deficits.

To quantify rapid alternating movements (RAMs) we used a simple prototype developed in our laboratory that requires the subject to rotate two hand-held foam spheres connected to optical encoders via flexible rods. Ninety-six participants, including 30 control subjects, 36 Cree subjects exposed to methylmercury, 21 subjects with Parkinson's disease, 6 subjects with cerebellar deficits, and 3 subjects with essential tremor, were involved in the study (though data for 5 were later removed). Twelve characteristics were developed and calculated from the raw data. Conditions examined included two hands at natural cadence (NC2), right and left hands separately at fast cadence (FCl), and both hands at fast cadence (FC2). Two ratios (FC2/NC2) and (FC2/FC1) combining these conditions were also examined. Test-retest reliability was >0.80 for most characteristics but was <0.70 for some characteristics, especially in the conditions executed at normal cadence. Correlations between characteristics and numbers of outliers with respect to the control group distribution were used to reduce the set of characteristics from 12 to 7 (i.e., duration, range, maximum slope, similarity in shape, smoothness, sharpness, and coherence). ANOVAs on the three largest groups generated significant results for most characteristics in the three conditions and the two ratios for Cree subjects and subjects with Parkinson's disease. ANOVAs on 3 age-matched groups (n=6) suggest that methylmercury affects the performance of the Cree subjects with the higher exposure, especially in terms of smoothness, sharpness, and coherence. These preliminary results suggest that this test is sufficiently specific and sensitive to characterize the performance of different groups of subjects. Ratios tend to improve discrimination for Cree subjects in a few characteristics but not for patients with Parkinson's disease.

Case-Control Studies↗

PubMed1999

Using frequency domain characteristics to discriminate physiologic and parkinsonian tremors.

The manner in which characteristics of time series in the frequency domain can enhance discrimination between physiologic and parkinsonian tremor when tremor amplitude is low was examined. Rest tremor and postural tremor with and without visual feedback were recorded twice in the two hands of a group of patients with Parkinson's disease (PD) (n = 21) and a group of healthy control subjects (n = 30) using displacement laser systems. Recordings were analyzed quantitatively using amplitude and seven frequency domain characteristics. Postural tremor with no visual feedback allowed the most efficient discrimination between the two groups of subjects especially in velocity and acceleration (derived from displacement) and allowed identification of more patients with PD as separate from the range observed in the control group. Moreover, the frequency domain characteristics that were investigated identified the majority of the patients even when amplitude did not. After eliminating redundant (correlated) characteristics, it was found that the frequency composition of tremor in PD can be described adequately with four characteristics, which are the most reliable, independent, and discriminative elements for detecting early or subtle modifications in tremor. Also, a series of finger flexions was found to enhance physiologic tremor but not tremor in PD. Discrimination of low-amplitude tremor in PD from normal physiologic tremor is enhanced by examining the median frequency of oscillations, the concentration of power in the power spectrum, and the distribution of power in particular ranges. Tremor measurement should not be limited to acceleration data as some information is more visible in velocity time series.

Acceleration↗

PubMed1999

Indexes for identification of abnormal tremor using computer tremor evaluation systems.

We consider methods of formulating indexes to identify abnormalities in tremor appropriate for computerized tremor analysis systems. Characterization of amplitude, frequency, and "harmonicity" are considered as well as how to combine several such characteristics into a single index to discriminate normal from abnormal tremor effectively. The methodological issues discussed here should be of interest to researchers and clinicians working with tremor in general and to both users and developers of computer tremor analysis systems.

Algorithms↗

PubMed1996

Can tremor be used to measure the effect of chronic mercury exposure in human subjects?

Clinical and quantitative studies in which tremor was used to evaluate the effect of chronic exposure to organic and inorganic mercury in human subjects during the last 20 years were identified in MEDLINE and BIOLOGICAL ABSTRACTS. In the selected studies, methods varied widely by types of transducers used, anatomical locations of tremor testing, tasks executed by the subjects, types of tremor recorded and durations of trials. Measurements of tremor in these studies also varied by frequency, amplitude, waveform and reproducibility. Typically measures of variability were not included. Results obtained depended heavily on the methods and analyses used. We suggest that, although many contradictions and discrepancies have been noted in these studies, tremor can probably be used to measure the effect of chronic mercury exposure. This would involve more rigorous and uniform recording procedures and analyses. Specific suggestions proposed include: realizing the limitations of accelerometric data; considering the effect of weight on the tested limb; controlling recording conditions; selecting samples more carefully; recording other physiological variables besides tremor; using tasks and manoeuvres that unmask subclinical abnormalities in tremor; reporting frequency, amplitude, waveform and variability of tremor; understanding the limitations of power spectra analysis; separating tremor characteristics according to types of mercury exposure; and considering supraspinal influences that both vision and voluntary movements have on tremor.

Environmental Exposure↗

PubMed1995

Myoclonic-like finger microdisplacements in patients with cerebellar deficits.

BACKGROUND: Here we assess the ability of patients with cerebellar disease to execute a simple visually-guided movement task involving tracking of a target with the index finger. METHODS: Spontaneous microdisplacements in index finger position are compared in patients with cerebellar deficits (ischemia [n = 3], multiple sclerosis [n = 3], degenerative cerebellar disease [n = 3]) and age-matched healthy subjects. Subjects were required to maintain a constant finger position relative to a stationary baseline displayed on an oscilloscope. RESULTS: Unusual transient abrupt movements (saccadic or myoclonic-like) directed with or against gravity were seen in patients whose neurological deficits were the most severe (7/9 patients). These abrupt myoclonic-like movements occurred independently of visual input, were not associated with clinically observable myoclonus, and were not detected previously in patients with Parkinson's disease. These abrupt myoclonic-like movements were not associated with abnormalities in either physiological tremor, or oscillations in finger microdisplacements induced by insertion of a delay (300-1400 ms) into the visual feedback of this finger "holding" experiment. An unexpected finding is that the results obtained for patients with cerebellar deficits by insertion of an experimental delay are not significantly different from those obtained with their age-matched controls. CONCLUSIONS: These observations suggest that abrupt myoclonic-like movements are a characteristic abnormality of patients with a variety of cerebellar deficits and emphasize the value of this simple motor tracking task for characterizing movement disorders.

Adolescent↗

PubMed1995

Effect of manipulating visual feedback parameters on eye and finger movements.

Thirteen healthy subjects were asked to maintain a constant index finger position in Experiment 1 or a constant eye position in Experiment 2 using visual feedback. The finger or eye position along with a stationary baseline target was displayed on an oscilloscope placed in front of the subject. Experiments 1 and 2 were carried out under sixteen combinations of delay and amplification of displacement on the screen (i.e., gain). In Experiment 1, increasing the gain in the visual feedback decreased the Root Mean Square (RMS) errors while increasing the delay increased these errors. An interaction between gains and delays was also observed in Experiment 1. In Experiment 2, the RMS errors were systematically higher than those recorded in Experiment 1 for the finger. No systematic pattern was recognized across all conditions of gains and delays for eye movements in Experiment 2. This study clearly illustrates differences in dynamics of motor control systems regulating eye and finger positions, respectively.

Eye Movements↗

PubMed1994

Early development of reaching in Down syndrome infants.

The development of reaching was studied in 10 Down syndrome and 10 control infants. Arm movements were recorded at 5, 7 and 9 months for the control group and 7, 9 and 11 months for the group with Down syndrome. Arm movements were recorded using a 3-dimensional video-motion analysis system. In both groups, there was a change from bilateral to unilateral responses with age, although Down syndrome infants used bilateral responses longer. Arm velocity increased significantly with age in the control group, but not in the Down syndrome group. Several characteristics of the reaching movements were clearly different between the Down syndrome and control groups. The deviations from a straight line and the changes in the plane of motion suggest that Down syndrome infants have more difficulty in controlling their arm movements. As expected, the results indicate the presence of a delay in the development of reaching in Down syndrome infants. They also suggest the presence of a deficit in the organization of their reaching movement.

Aging↗

PubMed1994

The measurement of tremor using simple laser systems.

Quantification of movement pathologies is an important challenge of the clinical and research laboratories today. Basically, two problems must be addressed. The first one is to find the appropriate technology; the second is to develop adequate measures from the raw data which will best discriminate between health and pathology. In this paper, we propose a simple method to record and analyse tremor and other microdisplacements of the upper extremities based on the recording of position by laser analog sensors. Any microcomputer equipped to perform analog-digital conversion is compatible for use with this system. The performance of the laser system is examined and compared with the performance of accelerometers. Finally, data recorded with a laser analog sensor from a patient with Parkinson's disease and a control subject are presented. This new laser-based quantitative method may prove to be an important tool in early and differential diagnosis of neurodegenerative diseases of the central nervous system.

Analog-Digital Conversion↗