Biomedical subjects

G E Stelmach

Publications and source records attributed to G E Stelmach.

At least 19 recordsLinked to original sources

PubMed1995

Progressive apraxia in clinically discordant monozygotic twins.

OBJECTIVE: To determine disease concordancy in the first identical twin with corticobasal degeneration. The patients were 63-year-old, erythrocyte antigen-confirmed monozygotic male twins who were clinically discordant for progressive apraxia caused by corticobasal degeneration. INTERVENTIONS: Neuropsychologic and kinesiologic testing, magnetic resonance imaging, and positron emission tomographic measurements of cerebral metabolic rate for glucose. RESULTS: The affected twin had lower neuropsychologic and kinesiologic test scores than did his brother, particularly on tests sensitive to right-compared with left-hemisphere function; widespread cerebral atrophy, worst in right parietotemporal cortices; and reduced whole-brain cerebral metabolic rate for glucose, worst in right posterior cortices. The clinically asymptomatic twin had normal neuropsychologic and kinesiologic test scores but performed more poorly on tests sensitive to left- compared with right-hemisphere function; had no abnormalities on magnetic resonance imaging; and had left temporoparietal as well as mild whole-brain hypometabolism. CONCLUSIONS: Corticobasal degeneration may remain clinically discordant in identical twins after 7 years. Positron emission tomography and neuropsychologic findings suggest the possibility of a preclinical stage of corticobasal degeneration. There is generalized cortical atrophy in patients with corticobasal degeneration in addition to focal atrophy.

Apraxias↗

PubMed1995

A neural model of basal ganglia-thalamocortical relations in normal and parkinsonian movement.

Anatomical, neurophysiological, and neurochemical evidence supports the notion of parallel basal ganglia-thalamocortical motor systems. We developed a neural network model for the functioning of these systems during normal and parkinsonian movement. Parkinson's disease (PD), which results predominantly from nigrostriatal pathway damage, is used as a window to examine basal ganglia function. Simulations of dopamine depletion produce motor impairments consistent with motor deficits observed in PD that suggest the basal ganglia play a role in motor initiation and execution, and sequencing of motor programs. Stereotaxic lesions in the model's globus pallidus and subthalamic nucleus suggest that these lesions, although reducing some PD symptoms, may constrain the repertoire of available movements. It is proposed that paradoxical observations of basal ganglia responses reported in the literature may result from regional functional neuronal specialization, and the non-uniform distributions of neurochemicals in the basal ganglia. It is hypothesized that dopamine depletion produces smaller-than-normal pallidothalamic gating signals that prevent rescalability of these signals to control variable movement speed, and that in PD can produce smaller-than-normal movement amplitudes.

Basal Ganglia↗

PubMed1995

Representation of hand position prior to movement and motor variability.

Pointing accuracy of six human subjects was measured in two blocked conditions where the hand was either never visible (T: target only) or only visible in static position prior to movement onset (H+T: hand+target). It was shown in condition H+T that, viewing the hand prior to movement greatly decreased end-point variability compared with condition T. This effect was associated with a significant modification of the movement kinematics: the H+T condition induced a shortened acceleration phase with a corresponding lengthened deceleration phase, compared with the T condition. These results led us to the hypothesis that viewing the hand prior to movement onset allowed a decrease of pointing variability through a feedback process. This hypothesis was further tested by turning the target off during the deceleration phase of the movement at half peak velocity. It was shown that turning the target off had no effect upon the T condition but induced a significant increase of pointing variability in the H+T condition. This result suggests that vision of the static hand enhances the proprioceptive localization of the limb and allows for a better visual to kinesthesic feedback.

Adult↗

PubMed1992

Interlimb coordination in Parkinson's disease.

This study examined the degree to which Parkinson's disease (PD) patients could "spatially link" the upper limbs to facilitate the performance of bimanual simultaneous movements. Six right-handed PD patients, and seven normal age- and sex-matched controls performed three different tasks: (a) an isotonic elbow flexion as rapidly as possible through an angle of 30 degrees; (b) an isometric contraction of the flexor muscles at the elbow joint to 40% and 60% of maximal volitional force (MVF) for a period of 5 s; (c) an isometric contraction for 2.5 s with one limb, then simultaneously performing an isotonic flexion with the contralateral limb while maintaining the isometric contraction for 2.5 s more. As expected, PD patients were significantly slower in performing the isotonic movement and produced lower peak velocities than the controls. More importantly, the two groups were differentially affected during the bimanual condition. In normals, movement time decreased and peak velocity increased in the bimanual condition. In contrast, PD patients showed increased movement times and sometimes decreased peak velocities in the bimanual condition. The results suggest that normal subjects utilize bilateral outflow to symmetrical muscle groups to synchronize the two limbs in the bimanual task, whereas PD patients dissociate the two limbs.

Aged↗

PubMed1992

Cognitive-motor abilities of the elderly driver.

This article reviews literature that documents the effects of age on motor performance as it relates to driving behavior. Movement initiation is the focal point of the first part of the article, and it is considered in terms of absolute age differences when functional manipulations are made, such as response preparation, response selection, response programming, and complexity. The second part of the article addresses age difference in the context of movement execution characteristics; differences in movement speed, force production, limb coordination, and sensory motor integration are considered. Movement time and movement kinematics and kinetics are the principal dependent measures reviewed. Adults were found to initiate and execute movements more slowly and with less precision as they age, which may contribute to the decline of their driving skill. Most of the data reviewed were obtained in laboratory settings; nevertheless, they suggest how age may impair the elderly driver.

Aged↗

PubMed1991

Age differences in visual sensory integration.

Numerous authors have reported that elderly persons are more affected than young adults when submitted to reduced or conflicting sensory inputs conditions. These results, however, do not permit to evaluate whether the elderly suffer from a reduced peripheral sensibility or from a deficit in the central integrative mechanisms responsible for configuring the postural set. The present experiment evaluated the ability of elderly to reconfigure the postural set when submitted to successive reduced and augmented visual sensory conditions. Results showed that young and elderly subjects' sway dispersion increased when they were exposed to a reduced visual sensory condition (i.e., vision/no-vision transition). However, when exposed to augmented sensory condition (i.e., no-vision/vision transitions) young adult were able to adapt rapidly and reduced their sway dispersion whereas the elderly exhibited an increased sway dispersion. This inability to adapt to an augmented sensory condition suggest that elderly persons, in addition to a reduced peripheral sensibility, have a deficit with central integrative mechanisms responsible for reconfiguring the postural set.

Age Factors↗

PubMed1991

Changes in electromyographic responses to muscle stretch, related to the programming of movement parameters.

Three experiments are reported that used the advance information paradigm which consists of providing subjects with either no or partial information about an upcoming movement. Subjects moved handles to control the vertical displacements of CRT beams, to point to eight targets. The illumination of different combinations of these targets prior to movement execution provided advance information about which hand, movement direction, or movement extent would be required. Reaction time (RT), integrated EMG activity in the forearm extensor and flexor muscles, and M1, M2, and M3 components of the stretch reflex responses triggered in these muscles were analysed as a function of the precued movement parameter. Compared to the no-information condition, RT decreased in all precue conditions; however, the reduction was greater when direction than when hand was precued, and greater when hand than extent was precued. The EMG activity of forearm muscles increased during the preparatory period in all precue conditions, but generally did not differ among them. An overall facilitation of the stretch reflex components was observed in all precue conditions. This facilitation: (1) was greater for flexor than extensor muscles, (2) was similar regardless of the degree of extent precued, (3) differed for the M2 and M3 components depending on whether the responding hand precued was ipsilateral or contralateral. When the precued movement direction was considered, similar changes in the M3 component were found in extensor and flexor muscles. M3 was facilitated when the muscle was precued as an agonist and was inhibited when it was precued as an antagonist. Collectively these data provide support for a motor programming conception of movement organization.

Adolescent↗

PubMed1991

Age differences in the maintenance and restructuring of movement preparation.

In 2 experiments, elderly and young subjects performed simple reaction time, choice reaction time, and movement plan restructuring tasks, using a stimulus precuing paradigm. In Experiment 1, the precue display (200 ms) and preparation interval (250, 500, 750, or 1,000 ms) were experimentally determined. In Experiment 2, the precue display interval was subject determined. For the restructuring task, the precue specified the response on 75% of the trials, enabling movement plan preparation with respect to movement parameters of arm and direction. On remaining trials, the precue incorrectly specified the response, requiring movement plan restructuring. Elderly, but not young, subjects restructured a movement plan for direction more quickly than for arm or for both parameters. These findings indicate that elderly individuals have poorer movement plan maintenance for direction than for arm and thus exhibit functional change in movement preparation processes relative to young individuals.

Adult↗

PubMed1991

Postural sway characteristics of the elderly under normal and altered visual and support surface conditions.

One of the most pervasive findings in the literature on the aged is the general slowing of cognitive-motor responses with advancing age. Hence, an increased slowness in the processing of information from vestibular, visual, and somatosensory systems could contribute greatly to a decline in postural stability. To examine this question, in a cross-sectional investigation, postural sway behavior of elderly (n = 18) and young (n = 10) adults was examined under conditions that stressed the slower integrative mechanisms rather than the reflexive mechanisms of postural control. The postural sway behavior of young and elderly subjects was examined for a prolonged duration (80 s), under altered visual and/or support surface (5 cm thick foam surface) conditions, and contrasted with normal stance. Results showed that the exclusion or disruption of one of the sensory inputs, alone, was not consistently sufficient to differentiate between elderly and young adults, because of compensation by the remaining sensory sources. Both alterations together (i.e., visual and surface), however, had a substantially greater effect upon the elderly than the young.

Adult↗

PubMed1991

Movement disorders--limb movement and the basal ganglia.

The primary concern of this article is to review experimental methods that may lead to a better understanding of the functional role of the basal ganglia in the control of movement. Two models of basal ganglia impairment are considered: Parkinson's disease and Huntington's disease. The review focuses primarily on akinesia and bradykinesia because they are key abnormalities of basal ganglia dysfunction. In general, through electromyography and kinematic analysis of movement, it may be possible to characterize specific movement disorders. Specifically, if damage sustained by the central nervous system is traced to a certain structure, it may provide insight on the extent of involvement and functional role of that structure in the control of movement. Much of the data reviewed suggests that the basal ganglia may play a specific role in the initiation and regulation of force control.

Basal Ganglia↗

PubMed1990

Postural muscle onset and voluntary movement in the elderly.

In young and elderly subjects, push and pull arm movements were executed during sitting or standing, under both simple reaction (SR) and choice reaction (CR) conditions. The combined reaction time (RT) results showed that CRT was larger than SRT in both groups. While sitting, the young group exhibited only slight change in RT, whereas the elderly group showed sizeable RT decrease. During standing, for the SR condition, the elderly's RTs were slightly slower than the young's; in contrast, for the CR condition, the elderly's RTs were substantially slower. Further, when the activation of ankle-stabilizer muscles was examined, it was found that postural muscle onset was essentially the same under both conditions. Focal-muscle onset and reaction time, under the choice condition, however, was sensitive to age-related differences. When these data are taken together, they suggest that the elderly may have an impaired postural system which is slow to stabilize the body prior to movement initiation.

Adult↗

PubMed1990

The influence of aging and attentional demands on recovery from postural instability.

It is well known that the risk of a debilitating injury from a fall is much higher for elderly than for young individuals. In addition, it is well documented that healthy elderly subjects exhibit increased postural sway during normal stance tasks. In the present experiment, we explored the notion that control of minor postural instability in elderly subjects is attention demanding. Postural sway of eight elderly (mean age = 70.0 years) and eight young (mean age = 20.0 years) subjects was measured under two different secondary demands during stable and mildly unstable upright stance. There were two types of work loads. Either a cognitive (math task) or motor (hand-squeeze) task was performed during the second segment of a 50-second standing trial. The effect of these work loads on mean velocity, range, and variability of range of center of foot pressure was measured during the destabilizing activity of arm swinging and subsequent recovery period. Following seven seconds of 1 Hz arm-swinging activity, elderly subjects showed a marked increase in recovery time to normal stance when concurrently performing an arithmetic task. This result suggests that recovery from a posturally destabilizing activity, involving proprioceptive and vestibular information, places increased attentional demands on the postural support system of the elderly.

Accidental Falls↗

PubMed1990

Temporal movement control in patients with Parkinson's disease.

Patients with Parkinson's disease (PD) have been reported to be unable to modify their movement velocity to adapt to changing environmental demands. For example, when movement amplitude is varied, PD patients usually exhibit a nearly constant peak velocity, whereas elderly subjects show an increase of their peak velocity with increased amplitude. The experiment examined the ability of PD patients to vary the duration of their movement (four different percentages of their maximum) under conditions where temporal, but not spatial, control was emphasised. PD patients had longer movement times than control subjects, but were able to vary the duration of their movement with comparable temporal accuracy to that of elderly subjects. For both groups, the agonist EMG activity increased with decreased movement duration. For the PD patients, the number of agonist bursts increased with increased movement duration.

Aged↗

PubMed1990

Practice effects on the preprogramming of discrete movements in Parkinson's disease.

The effects of practice on the simple and choice reaction times (RTs) of Parkinson's disease (PD) and control subjects in a discrete aiming task were analysed. For controls, practice led to a selective decrease in choice RTs, as has been reported previously. An opposite effect was seen in the PD group, with little change in choice RTs and substantial reduction in simple RTs. The results suggest that PD subjects can use advance information to initiate discrete movements more rapidly, but that this ability to "preprogramme" movements requires practice. Reconciliation of these results with studies reporting an inability to preprogramme in PD are made in a discussion of task characteristics which may allow or preclude preprogramming.

Attention↗

PubMed1989

Force production characteristics in Parkinson's disease.

This experiment examined the preparation and the production of isometric force in Parkinson's disease (PD). PD patients, elderly, and young subjects generated force levels that were a percentage of their maximum (15, 30, 45, and 60%). Subjects were cued on the upcoming target force level and they were asked to produce the required response as fast as possible. PD patients showed a similar progression of force variability and dispersion of peak forces to that of control subjects, implying they have an accurate "internal model" of the required forces. Force production impairments were seen, however, at the within-trial level. PD patients had more irregular force-time curves that were characterized by changes in the rate of force production. The results suggest a more "noisy" output from the motor system and an inability to produce smooth forces. PD patients were also substantially slower in initiating a force production and the delay was localized in the pre-motor reaction time.

Adolescent↗

PubMed1989

Preparatory processes in a case of hemi-parkinsonism.

Reaction times and movement times were recorded in a subject with parkinsonian symptoms confined largely to the left side of the body. Advance information concerning the movement was varied, being with complete, partial or no preparation. The results suggest that processing of preparation for the movement is not qualitatively different for the more affected side, but is substantially slowed.

Female↗

PubMed1989

Force transition control within a movement sequence in Parkinson's disease.

An experiment was performed which examined movement planning and force transition control in six patients with Parkinson's disease (PD) during a sequence of five finger taps at either a fast (200 ms) or slow (600 ms) temporal speed. The patients acted as their own controls and performed finger taps under three task conditions: (1) where all taps had to be of the same force intensity: no stress; (2) where it was known that one of the taps had to be executed with an augmented force: stress simple reaction time (SRT); and (3) where it was not known prior to initiation which one of the taps was to be more forcefully produced: stress choice reaction time (CRT). Reaction time data revealed a between-condition effect where stress SRT was faster than stress CRT and no stress was faster than both. Under both speed conditions, the interval after the stressed tap was profoundly lengthened. It was found that the lengthening was due to increases in both lift and dwell times for the slow tapping rate. In contrast, at the fast tapping rate, proportionately more of the interval increase was due to the increase in lift time. These findings suggest that patients with Parkinson's disease, when performing under a motor program mode, have difficulty in initiating a sequence and making a transition to lighter force levels after a stressed tap.

Aged↗

PubMed1989

Visuo-spatial processing in parkinsonians.

It has been suggested that patients with Parkinson's disease (PDs) may have problems processing visuo-spatial information and that this deficiency may contribute to the motor control problems observed in PD. However, most studies reporting visuo-spatial deficits are equivocal; they confound perceptual and motor processes. To address this issue, the present experiment systematically compared the relative contributions of several cognitive processes to performance: perception, stimulus-response translation, movement preparation and execution. Seven non-demented PDs and seven age-matched controls performed visual RT tasks, based upon judgements of spatial displacements. Both the RT and MT data suggested that PDs do not prepare movements as adequately as normals, and that PD deficits are associated with problems controlling movement execution. On the other hand, PDs were not slower in judging distances and linking perception to action, suggesting that previous findings of visuo-spatial deficits may be due in part to motor impairments.

Aged↗