Biomedical subjects

R Iansek

Publications and source records attributed to R Iansek.

At least 55 records · Page 3Linked to original sources

PubMed1994

Effects of hand and age upon abductive and adductive movements: a kinematic analysis.

Older and younger dextral subjects performed targeting movements to left and right with their preferred and nonpreferred hands upon a computer graphics tablet. Kinematic analysis revealed that older subjects produced larger constant errors than younger, paused more, and differed from younger individuals in a number of ways with respect to adductive/abductive asymmetries. The right hand was associated with shorter stroke durations and higher peak velocities, and both shorter times to peak velocity and from peak velocity to zero, suggesting superior ballistic preprogramming by the preferred right hand which was also more accurate. While both hands showed small abductive superiorities in terms of peak velocity and time from peak to zero, the largest directional asymmetries, stroke duration, showed leftward superiorities by both hands. We cannot therefore conclude either that experience with the rightward patterns of writing or that a reported tendency towards mirror-symmetrical movements by the two hands can account for the present results. Rather a right-hemisphere mediation of visually directed movements into left hemispace, along with a left-hemisphere mediation of fast, precise, temporal sequencing may jointly determine observable asymmetries. These may appear as a vector representing the opposing contributions of the two specialized hemispheres.

Adolescent↗

PubMed1994

Inaccuracy and instability of sequential movements in Parkinson's disease.

Animal studies suggest that the basal ganglia (BG) provide internal cues to trigger submovements in a movement sequence, with Parkinson's disease (PD) involving a deficiency in this cueing mechanism. However, it is not clear why defective internal cues can produce slow movements, or the extent to which slow movements are indeed the basic movement abnormality or are perhaps a compensatory mechanism for some other primary deficit. In this study we examined a number of the kinematic indices of matched fast movements between PD patients and age-matched controls, performed with and without reductions in visual cues for guidance, in order to delineate the relationship between the internal cue and the kinematic characteristics of these movements. Fourteen patients with PD, and their matched controls, used an electronic pen, which sampled pen-tip position at 200 Hz, and performed a sequence of drawing movements to nine targets upon a WACOM SD 420 graphics tablet. Subjects were trained to perform the movement sequence at a fast speed and were then required to perform the same movement at the same speed with reduced visual cues. Kinematic analysis indicated that, when visual cues were reduced, movements of PD patients became spatially and temporally unstable as they were progressively performed down the sequence. The instability was associated with an abnormal force profile increase in peak movement velocity and target overshoot, which became additive as the submovements progressed. We suggest that defective cue production is the basic deficit in parkinsonian hypokinesia. The defective cue leads to problems synchronising preparatory activity, which then results in abnormalities in movement forces which are characterised by unpredictable and inaccurate movement endpoints. When movements are strung together in a sequence the inaccuracy is additive leading to motor instability.

Aged↗

PubMed1994

Could bradykinesia in Parkinson's disease simply be compensation?

Even normal movements can be slow and hesitant. To distinguish between bradykinesia and the simple slow inefficiency sometimes seen in normal movement, we matched the movement durations of 12 patients with Parkinson's disease (PD) and 12 age-matched controls and examined end-point accuracy, number of submovements, force inefficiency, and relative duration of acceleration and deceleration phases of movement. Subjects used an electronic pen which sampled pen-tip position at 200 Hz, and performed a sequence of drawing movements to nine targets (0.5, 1, or 2 cm diameter) upon a WACOM SD420 graphics tablet. Patients could be trained to move at the preferred speed of controls (and vice versa). When moving at the same fast speed as controls, patient's movements were less accurate (increased end-point spread). Even when moving at their own preferred speed, patients' movements were less efficient (more submovements, more zero crossings in acceleration function) than controls moving at the same speed. If bradykinesia simply reflected increased caution and visual guidance, we would expect patients to exhibit prolonged decelerative phases of movement associated with terminal guidance. However, patients consistently required prolonged accelerative phases of movement, suggesting that there was a problem in generating appropriate movement forces to produce the required end-point accuracy. It is hypothesised that bradykinesia is not simply a compensation for defective preparatory processes, but may reflect a defective internal cue in PD which disrupts and impairs the outflow of motor responses.

Adaptation, Physiological↗

PubMed1994

Parkinsonian patients without dementia or depression do not suffer from bradyphrenia as indexed by performance in mental rotation tasks with and without advance information.

A predominant symptom of Parkinson's disease is akinesia and bradykinesia, slowing in the initiation and execution of voluntary movement. There has long been speculation as to whether cognitive processes undergo similar processes, but findings may be confounded by the frequent co-occurrence of dementia and/or depression. Mental rotation provides an internal or cognitive analogue of real movement, and enables us to determine the speed of such mental processes independent of any concurrent motor slowing in response initiation and execution. Medicated patients with Parkinson's disease who were free of dementia and depression were found to be able to mentally rotate alphanumeric or figural stimuli, with and without advance information as to the view (front or back) of a stick figure shortly to be shown, as rapidly as normal healthy controls. We conclude that cognitive processes involved in mental rotation are not necessarily slowed in Parkinson's disease.

Aged↗

PubMed1994

Allocation of attention to programming of movement sequences in Parkinson's disease.

The allocation of attention to the programming and execution of movement sequences was examined in Parkinson's disease (PD). The time taken to initiate and execute sequences of one, three, and five button taps was examined, while also varying the hand used (left or right) and the attentional resources that could be allocated to sequencing (using single- versus dual-task conditions). These results showed that performance anomalies in PD were most apparent with the preferred right hand under single-rather than dual-task conditions. Subjects suffering from PD may tend to divert attention from the right hand under single-task conditions, and perhaps with short sequences, as well as being less likely to prepare sequences of more than three movements in advance with that hand. These effects were unlikely to reflect asymmetric pathology. If the right hand of such subjects has in some respects now come to behave more like a "clumsy" left hand, this may reflect a deliberate strategic choice in an attempt to cope with a movement impairment.

Aged↗

PubMed1994

The pathogenesis of gait hypokinesia in Parkinson's disease.

To identify the fundamental deficit in gait hypokinesia in Parkinson's disease (PD) we conducted a series of experiments that compared PD subjects with age- and height-matched controls in their capacity to regulate either stride length, cadence (steps per minute) or both parameters to three conditions. In the first condition the spatial and temporal parameters of gait were documented for slow, normal and fast walking. The second condition compared parkinsonian gait with the walking pattern of elderly controls whilst controlling for two movement speeds: fast (control preferred) speed and slow (PD preferred) speed. In the third condition we examined the ability of PD subjects to regulate one parameter (e.g. stride length) when the other two parameters (e.g. velocity and cadence) were held at control values. A total of 34 PD subjects and 34 matched controls were tested using a footswitch stride analysis system that measured the spatial and temporal parameters of gait for a series of 10 m walking trials. Parkinsonian subjects exhibited marked gait hypokinesia in each of the experiments. Although they retained the capacity to vary their gait velocity in a similar manner to controls, their range of response was reduced. Within the lower velocity range, PD subjects could vary their speed of walking by adjusting cadence and, to a lesser extent, stride length. However, when the speed of walking was controlled, the stride length was found to be shorter and the cadence higher in PD subjects than in controls. Stride length could not be upgraded by internal control mechanisms in response to a fixed cadence set for age and height-matched velocity. In contrast, cadence was readily modulated by external cues and by internal control mechanisms when stride length was fixed to the values obtained for age- and height-matched controls. It was concluded that regulation of stride length is the fundamental problem in gait hypokinesia and the relative increase in cadence exhibited by PD subjects is a compensatory mechanism for the difficulty in regulating stride length. These findings are discussed in the context of the hypothesized role of the basal ganglia in generating internal cues for the maintenance of the gait sequence and in relation to the structuring of movement rehabilitation strategies.

Aged↗

PubMed1994

Age-related motor slowness: simply strategic?

BACKGROUND: While older adults typically exhibit slower hesitant movements, this may simply reflect a preference for a cautious movement strategy, rather than any pathological process. METHOD: To separate strategic preferences from any impairment in the coordination of movement, the present experiment trained older adults to move at the preferred speed of younger adults (and vice versa) in a simple zigzag drawing task on a digitizing tablet which sampled pen position at 200 Hz. Twelve older adults (mean age 69 yrs 8 mo) and 12 young adults (mean age 21 yrs) joined 9 targets 125 mm apart, of either 5, 10 or 20 mm diameter. Once the age groups were matched for movement duration, movement kinematics were examined to determine whether there were differences in the quality or accuracy of their movements. RESULTS: When strategic differences are controlled for, older adults performed the task with comparable overall accuracy, but exhibited greater hesitancy and more submovements. CONCLUSION: The results suggest a decline in motor coordination rather than any simple strategic preference for caution in movement. The hesitancy of movement to some extent parallels that seen in Parkinson's disease.

Adolescent↗

PubMed1994

Current status of the motor program.

Motor program theory has provided physical therapists with one approach to understanding how the brain controls movement. Analogous with computer programs that specify the operations of computer hardware, motor programs are thought to contain commands for muscles that allow movements to occur without the need for continuous peripheral feedback. A review of the physical therapy literature reveals many instances in which motor program theory has been used as a theoretical framework for clinical practice. Yet despite the contribution programming theory has made to the advancement of movement science, the motor program construct is currently under considerable threat. Keele's (1968) original definition no longer seems tenable, given the problems of program storage, motor equivalence, movement flexibility, and context-conditioned variability. The finding that researchers from different disciplines define the motor program in a variety of ways adds difficulty to the task of evaluating the efficacy of the model. A critical appraisal of programming theory and its use in physical therapy suggests that clinicians need to reconsider the usefulness of the motor program model as a basis for movement rehabilitation following brain damage and musculoskeletal disorders.

Humans↗

PubMed1994

Ability to modulate walking cadence remains intact in Parkinson's disease.

Gait hypokinesia (slowness) is a characteristic feature of Parkinson's disease. It is not clear, however, whether the slowness is due to a problem in regulation of the timing of consecutive steps or the control of stride size. Examination of cadence control for slow to medium walking speeds has shown an increase in step frequency that was a compensation for reduced stride length. In this investigation the ability of Parkinsonian patients to modulate their cadence (steps per minute) at the fast walking speeds exhibited by age and height matched controls was examined. The findings indicated that cadence control remains unaffected throughout its entire range in Parkinson's disease and that gait hypokinesia is directly attributable to an inability to internally generate sufficiently large steps.

Adaptation, Physiological↗

PubMed1994

Reduction in external cues and movement sequencing in Parkinson's disease.

To identify the focus of impairment in the performance of sequential movements of patients with Parkinson's disease, the extent of their reliance on external cues was examined. Eighteen patients with idiopathic Parkinson's disease and their matched controls performed a series of button presses at sequential choice points along a response board. The illuminated pathway to be followed successively extinguished ahead of each move according to three levels of reduction of external cues. Patients with Parkinson's disease were particularly disadvantaged with high levels of reduction of external cueing in terms both of movement preparation time (button down time) and movement execution time (movement time between buttons). Moreover, with high levels of reduction of external cueing, patients with Parkinson's disease were particularly subject to progressive slowing (movement time, not down time) further down the sequence. The basal ganglia may help generate internal cues for releasing successive stages of a predefined movement sequence.

Aged↗

PubMed1993

Motor functions of the basal ganglia.

A study of movement disorders such as Parkinson's disease and Huntington's disease can provide an indication of the motor functions of the basal ganglia. Basal-ganglia diseases affect voluntary movement and can cause involuntary movement. Deficits are often manifested during the coordination of fine multi-joint movements (e.g., handwriting). The disturbances of motor control (e.g. akinesia, bradykinesia) caused by basal-ganglia disorders are illustrated. Data suggest that the basal ganglia play an important role in the automatic execution of serially ordered complex movements.

Basal Ganglia↗

PubMed1993

Re-orientation of attention in Parkinson's disease: an extension to the vibrotactile modality.

Parkinson's disease (PD), a disorder of the dopaminergic nigro-striatal pathway, is associated with both motor and cognitive impairments, including perhaps the ability to focus attention. Disturbances of attentional processes were further examined in a series of vibrotactile choice reaction time (cRT) experiments involving biased probabilities of event occurrence, or valid/invalid precueing. Results of three experiments suggest that PD subjects, compared to controls, are less adept at maintaining attention in space. The performance of the PD subjects improved, however, when they were permitted to direct their gaze to one hand or the other, and when valid external precues were provided before each trial. Observed similarities between the cognitive and motor deficits of PD subjects support the notion that there is a close coupling between the mechanisms coordinating attention and movement.

Adult↗

PubMed1993

An evaluation of the role of internal cues in the pathogenesis of parkinsonian hypokinesia.

Our animal studies suggest that the basal ganglia provide an internal non-specific cue to trigger movement and imply that Parkinson's disease involves a deficiency in this cueing mechanism. Indeed parkinsonian patients typically rely upon external visual cues. To assess the effects of such non-specific cueing mechanisms on movement, we examined patients' utilization of a variety of auditory cues. Ten patients suffering from Parkinson's disease, and their matched controls, pressed buttons at a series of two-way choice points sequentially down a pathway, both when the latter remained illuminated throughout its length, and when it had to be followed from memory alone. In other experimental conditions, auditory cues were also provided, either contingent upon the previous response, at its initiation (a medium level of advance information) or at its completion (a low level of advance information), or as a series of regularly paced (non-contingent) auditory cues (from a metronome). In addition to error data, we recorded down time (DT, time to initiate each next response) and movement time (MT, time to execute each next response). However, both DT and MT measurements showed that parkinsonian patients were enormously disadvantaged by the absence of external cues. While contingent auditory cues were of some help, the performance of patients with Parkinson's disease was dramatically improved by the provision of non-contingent auditory information. Moreover, parkinsonian patients, unlike controls, were greatly affected by the length of individual sub-movements, especially in the absence of external cues. When the pathway to be followed remained illuminated, sub-movement length had little effect. We conclude that for well-learnt, predictable sequences the basal ganglia provide a non-specific internal cue that is necessary for switching between one movement and the next in a movement sequence, and also for development of preparatory activity for each sub-movement in the sequence.

Aged↗

PubMed1993

Coding of movement direction and amplitude in Parkinson's disease: are they differentially impaired (or unimportant)?

A recent study suggested that the preparation of movement direction, but not amplitude, may be selectively impaired by Parkinson's disease (PD). The authors examined the reprogramming of direction only, amplitude only, and direction and amplitude together, and included a control condition in which neither parameter was reprogrammed. The findings suggested that neither direction nor amplitude coding was differentially impaired in PD. Thus the structures affected by PD may not be uniquely involved in specifying only the direction or the amplitude of future movements; these structures probably have more complex higher-level roles.

Aged↗

PubMed1992

Programming of single movements in Parkinson's disease: comparison with Huntington's disease.

The preparation of individual finger movements was examined in Parkinson's disease (PD), in comparison with a similar study of Huntington's disease (HD). Motor programming was varied by increasing the amount of information available in advance of each movement. PD patients had particular difficulty when there was no cue light in advance of the movement, and when two upcoming movements were cued ahead of the current movement. Such difficulties suggest that PD patients may have difficulty in performing movements without sensory cuing, and in maintaining and organising a future sequence of movements. HD patients had been previously shown to have similar deficits. Commonalities in these once contrasted disorders probably arise from disruption of common mechanisms.

Adult↗

PubMed1992

Impairment in bilateral alternating movements in Parkinson's disease?

Although problems in bilateral simultaneous movements in Parkinson's disease (PD) are well known, such deficits have not been reported to be any more impaired than simultaneous movements within the same limb. This is surprising, since (a) the parallels between supplementary motor area (SMA) damage and PD are well documented and (b) the SMA seems to play a special role in bilateral motor control. Bilateral versus unilateral movements in PD were examined by using a task that compared alternating movements of fingers of the same hand with alternating movements of fingers of the opposite hands. PD patients showed particular problems in programming and transferring motor activity to fingers on the opposite side of the body, as opposed to switching motor activity between fingers on the same side of the body. These findings outline the relevance of SMA dysfunction to PD.

Aged↗

PubMed1991

A neural network model of neural activity in the monkey globus pallidus.

A 3-layer neural network model was constructed to determine the discharge patterns of neurons within the globus pallidus (GP) which would be required to run a sequence of movements at the motor cortical level. The model was based on the presence of tonic and phasic neuronal activity within the motor cortical region; that positive feedback was required to maintain tonic neuronal activity and that phasic neuronal activity was required to initiate and terminate the tonic neuronal activity. The model predicted the presence of both phasic and tonic activity within the middle layer (layer 2; GP) of the model in order for the motor cortical regions (layers 1 and 3) to be able to run and to maintain the movement sequence. This prediction was in keeping with our electrophysiological findings within GP.

Animals↗

PubMed1991

Motor function of the monkey globus pallidus. 1. Neuronal discharge and parameters of movement.

In order to examine the role of the basal ganglia (BG) in the regulation of basic movement parameters, we recorded extracellularly from pallidal neurons in conscious monkeys during the performance of a sequential wrist movement task which was composed of a series of holds and ballistic jumps. The movement sequence was predictable and had to be performed within specified time restraints. We recorded the activity of 297 neurons whose discharges were related to the movement task. We included only neurons whose discharges were related to movements at or about the wrist joint by prior examination outside the behavioural paradigm. Each neuron discharged preferentially to one direction of movement at or about the wrist joint. No consistent correlation was found between neuronal discharge and initial joint position, static load application, amplitude of movement or velocity of movement. The mean onset of neuronal discharge was 2 ms after the onset of EMG activity. The findings implied little contribution from the pallidal neurons in the execution of the current movement or to the movement's parameters. The implications are that the basal ganglia are likely to be concerned with other aspects of movement control.

Animals↗