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Biomedical subjects

N Mai

Publications and source records attributed to N Mai.

At least 37 records · Page 2Linked to original sources
PubMed1999

Visual control of automated handwriting movements.

This study provides new insight into the subtle interaction between visual feedback and automated handwriting movements. To separate effects of visual feedback from effects of speed/accuracy trade-off, subjects were trained to perform the tasks with rapid and automated movements. To control the visual feedback the written trace was presented only on a computer screen. In the first experiment the visual feedback of script size was manipulated. Subjects had to write the character combination "ll" onto a pattern of squares. In some trials the script size was unpredictably enlarged by 133% or reduced by 66%. Results showed that the ongoing "l" was not affected by the manipulation, but subjects adapted script size in the following "l" without any change in the kinematic characteristic of the movements. In a second experiment trajectory correction strategies in perturbed writing movements were studied. Two small boxes had to be connected by rapid and single-stroke movements. In some of the trials the position of the target box was changed unpredictably to a new position. Kinematic analysis revealed that the initial movement was not aborted, but rather a second independent movement was added to correct the trajectory to the new target. Thus, this proves that a distortion of visual feedback does not directly slow down open-loop movements to allow control of the motor output in a closed-loop mode. The ballisticity and automation was maintained during movement correction. Our findings fit perfectly well with recent theories of kinematic organization where complex movements are composed by elemental movement strokes.

Adolescent↗
PubMed1999

Prehension with the ipsilesional hand after unilateral brain damage.

Sensorimotor deficits in the hand ipsilateral to a brain lesion have been reported in different motor tasks. We evaluated performance of the ipsilesional hand in 12 patients with either left (LBD) or right brain damage (RBD) by kinematic analysis in order to precisely characterize possible deficits in the two components of prehension (transport and grasp). Both patient groups exhibited performance deficits in the main kinematic parameters, e.g., reduced velocity of the transport component and prolonged movement time. However, while LBD patients showed a more general slowing, RBD patients prolonged in particular the last phase of the movement toward the object. We suggest that relevant visuospatial representations and the adequate mapping of motor processes may be impaired after RBD. In contrast, LBD caused a more unspecific disturbance pattern, supporting the view that the precise parameterization of motor programs is impaired. Maximum grip aperture was normal in both patient groups. However, since aperture could be biased by slowed movement, the notion that the grasp component was preserved remains speculative. The patient's ability to scale the maximum velocity of the transport component to adapt to changes in movement amplitude and to scale the maximum hand aperture of the grasp component to adapt to object size was preserved in both groups. Thus both hemispheres can have competence for this scaling mechanism.

Adult↗
PubMed1999

Comparative analysis of diadochokinetic movements.

Tests of diadochokinesia are an inherent part of a neurological examination. Various quantifying methods have been proposed to increase the objectivity, sensitivity, and reliability of such examinations. The methods used and analyses performed, however, differ substantially between tasks. We used a three-dimensional, ultrasound-based recording device to continuously record joint angles during three diadochokinetic movements, avoiding any external constraints of the movements. Alternate pronation and supination of the forearm, tapping with the whole hand and with the index finger in isolation were analyzed in a sample of 63 healthy control subjects. The most sensitive measure for capturing effects of gender, sex, and active hand was frequency. The right hand was faster than the left in all tasks, tapping performance declined with increasing age, and male subjects were faster than females in forearm diadochokinesia. Other measures that characterize speed of movement such as maximum angular velocities and accelerations did not yield comparable sensitivity in detecting the same statistical effects. However, angular velocity achieved the highest test-retest reliability for forearm diadochokinesia, while frequency was reproduced in the tapping tasks. Additional measures characterizing symmetry of the angular velocity profiles and intraindividual variability were shown to be largely independent of movement speed. Examples in neurological patients showed that the data define a valuable standard against which pathological performance can be precisely evaluated. In addition, the different measures captured dissociable aspects of motor performance that may further help to characterize the deficit and adjust therapy.

Adult↗
PubMed1999

Characteristic MR lesion pattern and correlation of T1 and T2 lesion volume with neurologic and neuropsychological findings in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

BACKGROUND AND PURPOSE: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an arteriopathy related to a genetic defect of the notch 3 gene on chromosome 19. The purpose of this study was to evaluate lesion distribution and volume using MR imaging and to correlate the lesion volume with the neurologic and neuropsychological findings. METHODS: Twenty members of two families (14 with CADASIL as determined by linkage analysis, six healthy) were studied with MR imaging. Two observers evaluated the MR findings semiquantitatively and quantitatively. MR results were then correlated with neurologic and neuropsychological findings. RESULTS: A typical pattern of lesion distribution in patients with CADASIL was found: the frontal lobe was the site with the highest lesion load, followed by the temporal lobe and the insula. The total lesion volume on T1-weighted MR images correlated significantly with the degree of disability and the degree of impairment in neuropsychological functions (including attention, memory, and conceptual and visuospatial functions). CONCLUSION: In CADASIL patients, a common pattern of cerebral lesion distribution is found. The total T1 lesion volume is an important parameter to correlate with disability, as it may prove to be helpful in predicting the natural history of the disease.

Adult↗
PubMed1996

Computational analysis of open loop handwriting movements in Parkinson's disease: a rapid method to detect dopamimetic effects.

We used a computational analysis of open loop handwriting movements and a clinical rating scale for monitoring the effect of apomorphine in 16 patients with early untreated parkinsonism [subsequently L-DOPA responsive, probable Parkinson's disease (PD)], six patients with long-standing PD with L-DOPA associated motor fluctuations, and seven patients with known L-DOPA unresponsive parkinsonism. Subjects were instructed to write fluently concentric circles of approximately 12 mm in diameter. Movements were recorded for two periods of 3 s each, using a digitizing tablet. Mean peak velocity (Vmax) and mean peak acceleration (Amax) were determined. In addition, two sensitive indices describing the degree of automation of handwriting were derived: (a) NCV, calculated as the mean Number of Changes in direction of Velocity per half circle, and (b) NCA, the mean Number of Changes in the direction of Acceleration. Clinical rating was performed according to the Unified Parkinson's Disease Rating Scale part III (UPDRS III). After apomorphine injection, the patients with early untreated probable PD showed significant improvement of Vmax, Amax, NCV, NCA, and UPDRS III scores. Likewise, the patients with long-standing PD improved significantly in all kinematic parameters and UPDRS III scores. Patients with L-DOPA unresponsive parkinsonism failed to change significantly in any of the parameters tested. These observations suggest that the computer-assisted analysis of automated handwriting movements can be used as an objective quick method for quantifying dopamimetic effects on the kinematics of handwriting movements in parkinsonian patients.

Adult↗
PubMed1996

Persisting "writer's cramp" as a result of compensation of a temporary palsy due to a hereditary neuropathy with liability to pressure palsies.

A 49-year-old man reported several periods of acute paresis of different nerves after exposure to pressure. All palsies showed a good recovery over a period of days to months. The suspected diagnosis of a hereditary neuropathy with liability to pressure palsies was confirmed by the histology of a suralis nerve biopsy, which showed a distinct tomaculous swelling of the myelin. Nine years ago he noticed an acute, distally pronounced palsy of the right arm. A brachial plexus lesion was diagnosed. His profession required written work, thereby forcing him to compensate this weakness by increasing the coactivation of the elbow and upper arm. This coactivation persisted even after complete recovery from the plexus palsy. Thus, the patient showed the typical feature of classical writer's cramp, with broad coactivation of the arm muscles, which has continued to the present. At the same time, however, the patient was able to perform other motoric tasks well, such as painting. After several practice sessions with a special program that makes use of preserved motor abilities to reestablish writing, the patient was again able to write with a normal kinematic profile as documented by the recorded handwriting. This suggests that the "writer's cramp" of our patient is one form of task-related dystonia that may be related more to the perserveration of a misleading motor strategy than to a general inability of the motor system to control the movement properly.

Brachial Plexus↗
PubMed1996

Kinematic analysis of movement imitation in apraxia.

Accuracy of the final position and kinematics of movement were analysed during the imitation of meaningless gestures in patients with unilateral brain lesions who performed with the hand ipsilateral to the lesion and in control subjects. Controls imitated the gestures virtually without spatial errors. The kinematics of their movements was characterized by single-peaked and approximately bell-shaped velocity profiles of the transport phase combined with no or only minor corrective movements in the final phase. Patients with right brain damage (RBD) performed as well as control subjects with respect to both spatial accuracy of final hand-positions and kinematic parameters of the movement trajectories. Patients with left brain damage (LBD) committed spatial parapraxias and had a much higher frequency of kinematic abnormalities. However, there was no correlation between kinematic abnormalities and apraxic errors. There were kinematically abnormal movements which reached a correct final position as well as kinematically normal movements leading to apraxic errors. One possible explanation for the combined occurrence of kinematic abnormalities and parapraxias in LBD patients would be that they are independent sequels of left hemisphere lesions. An alternative account is that the associations and dissociations result from an interaction between one common basic deficit and strategies to cope with this deficit. The basic deficit may concern the mental representation of the target position. The LBD patients may react to the absence of an appropriate representation of the target by one of two alternative strategies; they may switch to a strategy of slowed, on-line controlled movements to find the required final position, or they may move their hand smoothly at normal speed to a roughly specified location without taking note of their deficiency. Depending on whether these strategies are successful or not they would lead to the observed associations and dissociations between kinematic abnormalities and spatial parapraxias.

Adult↗
PubMed1995

Double-blind crossover study with levorotatory form of hydroxytryptophan in patients with degenerative cerebellar diseases.

OBJECTIVE: To determine whether treatment with the levorotatory form of hydroxytryptophan (L-5-hydroxytryptophan), a controversial experimental drug, can improve the conditions of patients with ataxia. DESIGN: A double-blind crossover study with the levorotatory form of hydroxytryptophan was performed in 39 patients with degenerative cerebellar diseases. SETTING: Patients were selected from an ongoing prospective follow-up study at two university hospitals. PATIENTS: We studied 19 patients with Friedreich's ataxia, 13 with cerebellar atrophy, and seven with olivoponto-cerebellar atrophy. INTERVENTION: The levorotatory form of hydroxytryptophan was given orally in a dose of 1000 mg/d. Each treatment phase, with the levorotatory form of hydroxytryptophan or the placebo, lasted 10 months, after which the treatment of patients was crossed over to the other phase. MAIN OUTCOME MEASURES: Ataxia was documented and quantified by using a clinical score, posturography, and measurement of grip force and the rapid-syllable repetition rate. RESULT: The levorotatory form of hydroxytryptophan had no significant effect on cerebellar symptoms. CONCLUSION: Long-term treatment with a high dose of the levorotatory form of hydroxytryptophan does not improve the conditions of patients with ataxia.

5-Hydroxytryptophan↗
PubMed1995

Persistent mirror movements: force and timing of "mirroring" are task-dependent.

A simple isometric motor task was used to quantify intended and unintended finger movements in two subjects (father and son) with persistent mirror movements. One hand voluntarily changed grip force between thumb and index finger at different amplitudes and frequencies, while the other hand was to maintain a constant force. During all experimental conditions the "steady" hand showed insuppressible, highly cross-correlated contractions, compatible with bilateral distribution of a single motor command to the spinal cord. However, these associated movements were not strictly mirror images, nor did they show a fixed relationship to the voluntary movements across experimental conditions. The ratio of mirror to voluntary movement ranged from 1.4 to 19.1% and from 3.4 to 78.4% in the two subjects and was directly related to voluntary strength and speed. At maximum speed, mirror activity tended to precede voluntary activity, while it was delayed in slow force changes. Comparable time lags were not found in control subjects instructed to simulate mirror movements. We conclude that neuronal mechanisms in addition to bilateral corticomotoneuronal connections are at work in persistent mirror movements.

Adult↗
PubMed1995

Feedback-based training of grip force control in patients with brain damage.

OBJECTIVE: Feedback-based training of grip force control in patients with various brain lesions was evaluated. DESIGN: Patients were instructed to hold a force transducer in a precision grip and to track with their grip force a moving target, which was presented together with the feedback signal on a monitor. Training performance was evaluated during a maximum of 10 sessions. Before and after the training, performance in two transfer tasks, which differed in target characteristics from the training task, was examined. PATIENTS: Ten patients with impaired grip force control, after brain lesions of different origin, were selected on the basis of a clinical examination of hand function. MAIN OUTCOME MEASURES: Tracking accuracy in training tasks and transfer tasks was evaluated by calculating the conventional root-mean-square error. RESULTS: Nine out of the 10 patients reduced their tracking error considerably during a maximum of 10 subsequent sessions (t test, p < 0.05), and most of them reached normal or near-normal performance. In addition, they improved in both transfer tasks (t test, p < 0.05). Detailed analysis showed that impaired initial performance and improvement was not uniform among patients and could be attributed to individual aspects of force control. CONCLUSIONS: In view of these results, a feedback-based training of grip force may be a useful enrichment of motor therapy.

Adult↗
PubMed1994

Perturbation of precision grip in Friedreich's ataxia and late-onset cerebellar ataxia.

Perturbations of precision grip were tested in 7 patients with Friedreich's ataxia (FA) and 11 patients with late-onset cerebellar ataxia (CA). Subjects were instructed to hold a small compressible manipulandum between thumb and index finger and to resist any perturbation of maintained finger position. A sudden increase of load induced a displacement of fingers until this was stopped by subjects' active intervention. The amount of initial displacement emerged as a highly sensitive parameter to differentiate the clinical subgroups: Responses in FA patients were missing or massively delayed, whereas displacements in CA patients were normal or only moderately abnormal. This discrimination of impaired hand function in FA and CA patients has not been possible by using only tasks of isometric grip force control. We concluded that our task relies more on intact sensory afferents, which are known to be impaired in FA, than on cerebellar function. In a second task the stiffness of the maintained grip was determined. On the average, preresponse stiffness was lower in FA patients as compared with CA patients and normal controls. However, stiffness appeared to be an independent parameter that did not influence the amount of displacement in the perturbation task.

Adolescent↗
PubMed1994

A computational procedure for movement analysis in handwriting.

Validity of handwriting movement data recorded with digitizing tablets is poorly reflected by manufacturer's specifications. Actual errors of positional data are in fact in a critical range, in particular when time derivatives are calculated. Because differentiation magnifies errors in the displacement data, data smoothing becomes crucial. A new method for smoothing and differentiating noisy handwriting movement data is proposed. Non-parametric estimation of regression functions using kernel estimates generally offers simple application and extremely fast calculation. Assessing simulation data the efficiency of the procedure was investigated and compared with butterworth filters and finite impulse response (FIR) filters. Kernel estimates show a slightly elevated bias, but strongly reduced residual variance in the velocity and acceleration signals. The overall smoothing behaviour of kernel estimates is better than butterworth filters and very similar to FIR filters, if their transition band is chosen appropriately.

Electronic Data Processing↗
PubMed1992

Creatinine and N-methylhydantoin degradation in two newly isolated Clostridium species.

With N-methylhydantoin (NMH) as the main organic substrate, two strictly anaerobic spore forming Gram-positive bacterial strains were isolated from sewage sludge. These strains, named Clostridium sp. FS23 and Clostridium sp. FS41, totally degraded NMH, via N-carbamoylsarcosine (CS) and sarcosine as intermediates. Strain FS23 grew also with creatinine, which was converted to NMH by creatinine iminohydrolase (EC 3.5.4.21). This enzyme was formed at high rates with all substrates tested. Cytosine and 5-fluorocytosine were not utilized as substrates by creatinine iminohydrolase preparations purified to a homogeneity of 98%. NMH amidohydrolase (NMHase) and N-carbamoylsarcosine amidohydrolase (CSHase) turned out to be inducible in both strains. Other than in aerobic organisms, NMHase from these two isolated did not require ATP for enzymatic activity. SH-group protecting agents were not necessary for stability.

Adenosine Triphosphate↗
PubMed1991

Changes in perceived finger force produced by muscular contractions under isometric and anisometric conditions.

We compared matching of finger forces under isometric conditions with matching of forces produced against a spring load (anisometric conditions) in twenty normal subjects. The instruction was to generate the same force in both hands holding a grip between thumb and index finger in each hand. Visual feedback indicating the target force and the actual force applied were presented for one (reference) hand only. The forces produced in each hand were measured continuously during matching trials. A special device provided the opportunity to change from isometric to anisometric force production. Matching was required under symmetric conditions, in which force was generated in both hands either isometrically or anisometrically, as well as under asymmetric conditions in which isometric force has to be matched to anisometric force or the reverse. Under symmetric conditions matching error was consistently smaller in anisometric than in isometric force production. However, the striking feature was a severe mismatch between hands when forces had to be produced differently. For most subjects, a force generated against the spring load in the reference hand was greatly overestimated by the matching hand working isometrically. For the reverse condition consistent underestimations were observed. This effect cannot be attributed to left/right differences or a simple confusion of subjects in the asymmetric tasks. Some of the factors confounded with the conditions of force production were ruled out as an explanation by additional experimental controls. The mismatch neither depends on signals related to different finger positions associated with target forces nor is it alleviated when differently produced forces are matched sequentially.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Disturbance of movement vision after bilateral posterior brain damage. Further evidence and follow up observations.

In 1983 we reported in this Journal a patient who suffered a disturbance of movement vision in a relatively pure form. This uncommon cerebral visual deficit resulted as a consequence of bilateral brain damage affecting the lateral temporo-occipital cortex and the underlying white matter. In this paper we present further evidence for the selectivity of the movement vision deficit. Furthermore, follow-up examination did not reveal any significant change which indicates that the disorder appears irreversible. Magnetic Resonance Imaging (MRI) shows bilateral lesions involving the upper (cranial) part of the occipital gyri and the adjacent portion of the middle temporal gyri, with the main focus of damage in the upper (cranial) banks of the anterior occipital sulcus. In addition, cortico-cortical fibre pathways interconnecting occipital, temporal and parietal 'visual' areas are also affected bilaterally. The selectivity of the movement vision deficit and the irreversibility of the disorder strongly support the idea that movement vision is a separate function which is subserved by a visual pathway specialized for the processing of visual motion.

Brain Diseases↗
PubMed1991

[Health and handicap profile of patients with cerebrovascular diseases in an inpatient rehabilitation center].

In order to get more precise information on the staffing and structural capacities needed in the care and rehabilitative treatment of patients with cerebrovascular diseases (CVD), the profiles of illness and disability were studied retrospectively on the basis of the medical histories of CVD patients who had been treated at a neurological rehabilitation centre in 1987 and had mostly come from the facility's assigned catchment area. Due to insufficient documentation of certain profile data in the patients histories, the same data were recorded in a complementary study for all patients in this target population admitted in the first half of 1988. The classification of patients into nursing care categories, already practiced in everyday clinical routines, turned out a valid global estimate for the total nursing, medical and therapeutic efforts required in the individual patient. A high correlation exists between the nursing care category assigned and the numbers of necessary care interventions as well as functional disorders requiring rehabilitative attention. The nursing care interventions needed concentrate on certain situations during the day, which has to be taken into account in staff planning. Given the multitude of impairments and disabilities seen, comprehensive management in a neurological rehabilitation unit presupposes a team of diverse diagnostic and therapeutic specialists, which, apart from medical specialists and nursing staff, should at least comprise physio- and Occupational Therapists, neuro-linguistic or logopedic specialists, as well as psychologists. In view of the high incidence of accompanying internal diseases, a stroke rehabilitation unit must have access to an internal medical service at least on a consultancy basis, and available on an extended time scale.

Activities of Daily Living↗