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Biomedical subjects

W Hening

Publications and source records attributed to W Hening.

33 records · Page 2Linked to original sources
PubMed1991

Organization of voluntary movement.

There have recently been a number of advances in our knowledge of the organization of complex, multi-joint movements. Promising starts have been made in our understanding of how the motor system translates information about the location of external targets into motor commands encoded in a body-based coordinate system. Two simplifying strategies for trajectory control that are discussed are parallel specification of response features and the programming of equilibrium trajectories. New insights have also been gained into how neural systems process sensory information to plan and assist with task performance. A number of recent papers emphasize the feedforward use of sensory input, which is mediated through models of the external world, the body's physical plant, and the task structure. These models exert their influence at both reflex and higher levels and permit the preparation of predictive default parameters of trajectories as well as strategies for resolving task demands.

Animals↗
PubMed1991

A clinical and polysomnographic comparison of neuroleptic-induced akathisia and the idiopathic restless legs syndrome.

Neuroleptic-induced akathisia (NIA) is motor restlessness caused by dopamine receptor blocking antipsychotic agents. Nine patients with NIA and 11 patients with idiopathic restless legs syndrome (RLS) were studied polysomnographically. The sleep disturbances were milder in NIA than idiopathic RLS but increased numbers of awakenings and decreased sleep efficiencies were common to both groups. In addition, RLS patients demonstrated prolonged sleep latencies. Periodic movements in sleep (PMS) were present in only 5 of 9 patients with NIA but in all 11 patients with idiopathic RLS. In no NIA patient did we see the multiple, large amplitude, violent, resting myoclonic jerks of the legs that we saw during wakefulness in some of our more severe cases of idiopathic RLS. NIA patients tended to experience inner restlessness and idiopathic RLS patients tended to experience leg paresthesias as an antecedent to motor restlessness. Idiopathic RLS patients had symptoms that were worse at night and in repose far more frequently than patients with NIA. NIA and idiopathic RLS have similarities and differences. Because both NIA and idiopathic RLS are characterized by motor restlessness and sleep disturbances, the pharmacodynamics of antipsychotic medications may give clues as to both the cause and treatment of idiopathic RLS.

Adult↗
PubMed1990

Variable expressivity in familial restless legs syndrome.

A 62-year-old man with a 20-year history of excessive daytime somnolence and kicking during sleep was an obligate carrier of the restless legs syndrome gene because his paternal grandfather, father, and all three of his children had symptoms of restless legs syndrome. The patient himself, however, denied motor restlessness after a careful and exhaustive medical history and he was originally believed to have periodic movements in sleep without restless legs. Close clinical observation did reveal nighttime motor restlessness, although the patient continued to deny its importance. Polysomnography showed frequent periodic movements in sleep. We conclude that there can be variable expressivity of the clinical features in familial restless legs syndrome and that there are probably some relatively nonrestless patients with prominent periodic movements in sleep who are carriers of the restless legs syndrome gene. Some sleep-disordered patients who are believed to have only periodic movements in sleep may have a forme fruste of autosomal dominant restless legs syndrome. If one does not examine these patients carefully at night and take an adequate family history, one may miss the diagnosis of restless legs syndrome.

Gene Expression↗
PubMed1990

Trajectory control in targeted force impulses. VII. Independent setting of amplitude and direction in response preparation.

We have previously shown that when aiming impulses of force to unpredictable flexion and extension targets, subjects prepare themselves to respond by preselecting a default amplitude and direction. In our preceding study, where flexion and extension target ranges were symmetrical, subjects prepared a single default amplitude near the center of each of the two ranges and selected a default direction arbitrarily (Favilla, Hening et al. 1989). Following target presentation, amplitude and direction were specified gradually and in parallel. By using an experimental paradigm in which target amplitudes had unequal probabilities in only one of the two directions, we no sought to determine to what extent the default amplitude prepared by subjects is dependent on the default direction that is selected for a given trial. Five normal subjects produced isometric elbow flexion and extension force impulses to match four targets requiring responses of two amplitudes in each direction. Flexion and extension targets were of the same size. In all biased probability conditions, targets were presented in unpredictable order and, in one direction, the probability of occurrence of the targets was biased (80% versus 20%). In the other direction, the two targets were equiprobable. To maximize the effect of the default settings on response parameters, we required subjects to initiate their response in synchrony with a predictable tone occuring less than a reaction time subsequent to the presentation of the visual target. Such a short interval was chosen to disclose the default parameters selected by limiting the influence of the target just presented on the amplitude and direction of the subjects' responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Trajectory control in targeted force impulses. VI. Independent specification of response amplitude and direction.

The preceding study of this series (Hening, Favilla and Ghez 1988) examined the time course of the processes by which human subjects use information from a target to set the amplitude of an impulse of isometric elbow force. In that study, subjects were provided with separate cues to time response initiation and to inform them of the required amplitude of the response. When the time between target presentation and response initiation was too brief for them to incorporate information from the target, subjects produced default responses whose amplitudes reflected their prior experience. At longer latencies, subjects specified response amplitude with a gradual time course, starting earlier and ending later than an average reaction time. The present study now examines how two distinct response features, amplitude and direction, are specified following presentation of a target. We sought to answer three main questions. What are the features of responses that are produced before target information is available? Are direction and amplitude specified serially or in parallel? Does the specification of one response feature interfere with the specification of the other? Six normal subjects were studied. They were trained to initiate impulses of isometric elbow force in synchrony with the last of a predictable series of regular tones. The amplitudes and directions were to match those of visual targets requiring flexions or extensions with one of three amplitudes. The targets were presented at random times (0-400 ms) before the last tone. Target directions and amplitudes were either predictable (simple condition) or unpredictable (choice condition). In the simple condition, response amplitudes and directions were independent of the interval between target presentation and response onset (S-R interval). In the choice condition, both amplitude and direction varied with the S-R interval. At short S-R intervals (less than 100 ms), the direction of the subjects' responses was not related to that of the target. The amplitudes of the responses were near the centers of the two target ranges. With increasing S-R intervals, the proportion of correct direction responses gradually increased. Over the same range of S-R intervals, the amplitudes of both right and wrong direction responses to the different targets separated and converged on their respective target amplitudes. Specification of both direction and amplitude was complete at S-R intervals greater than 300 ms. The time course of amplitude specification in this bidirectional paradigm was prolonged over that in a paradigm where response direction was predictable.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1989

Gradual specification of response amplitude in human tracking performance.

These experiments examine how human subjects use information from a target to trigger a response and to specify its trajectory. We first determined if response initiation is predicated on the prior specification of response amplitude by examining the latencies and trajectories of impulses of isometric elbow flexion aimed to one of three visual targets. We varied target predictability (simple versus choice), the urgency with which the response was required, and the level of practice. With practice, subjects could respond to unpredictable targets with the same latency as to predictable ones; the range of response amplitudes was, however, always constricted. This central tendency bias disappeared when subjects were allowed long latencies to respond to the target, suggesting that with urgency, subjects can respond before specification is complete. To determine the time course of specification, the subjects were trained to initiate force impulses in synchrony with the last of a series of predictable tones. They also attempted to match the amplitude of their force impulses to one of three unpredictable visual targets presented at randomly varying times (50-400 ms) prior to the synchronizing tone. At the shortest stimulus-response intervals, before target information could be processed, the amplitudes of responses to all targets were clustered around that of the middle-sized target. Then, as the stimulus-response interval increased, response amplitudes gradually converged upon their specific targets. Specification started at stimulus-response intervals of about 100 ms and extended until about 350 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Trajectory control in targeted force impulses. IV. Influences of choice, prior experience and urgency.

The present study examines the influences of target predictability, level of practice and response urgency upon the latency and trajectory of a simple motor response. This response is an impulse of isometric force produced by the index finger and aimed to match a step change in a visual target. As expected (Welford 1980), the responses of naive subjects responding as soon as possible after target presentation were initiated at longer latencies when the target steps were of unpredictable amplitudes (choice condition) than when their amplitudes were all the same (simple condition). This choice effect on response latency diminished progressively with practice and eventually disappeared. The trajectories of urgently produced choice responses, however, differed from those of simple responses, and this difference was not reduced by practice. Choice trajectories were more variable and showed a systematic distortion in scaling: response amplitudes exhibited a central tendency bias, or range effect. When targets were equiprobable, responses were biased towards the middle sized target while responses aimed at targets of unequal probability were biased towards the most probable. This effect was independent of the absolute amplitudes of the responses required and was not associated with deviations from the pulse height control policy (Gordon and Ghez 1987a) that human subjects use to vary the amplitude of force impulses. The distortion in scaling and the increased variability of responses aimed at individual targets were markedly reduced when urgency was relaxed and subjects could respond when ready. Then, both simple and choice responses were proportionally scaled to the target, but choice responses were initiated at longer latencies. The changes in trajectory of urgent responses suggests that their inaccuracy occurs because the subjects initiate their responses before the specification of amplitude is complete. The central tendency bias of such incompletely specified responses suggests further that, prior to target presentation, subjects prepare a default response reflecting their expectations. This default may then be modified by information obtained from the target in a process that lasts longer than a minimal reaction time.

Adult↗
PubMed1988

Trajectory control in targeted force impulses. V. Gradual specification of response amplitude.

This study was undertaken in order to determine the time course of the process by which information derived from a visual target is used to accurately set the amplitude of a simple motor response. We refer to this process as response specification. Separate auditory and visual cues were given to the subjects in order to independently control the moment of response initiation and the time available for processing amplitude information from the target. Six subjects initiated impulses of isometric force in synchrony with the last of predictable series of regular tones. Response amplitudes were to match one of three visual target steps occurring at random times between 0 and 400 ms before the response-synchronizing tone. Using these separate auditory and visual cues, we were able to systematically vary the time interval between target presentation and response onset, termed here Stimulus-Response or S-R interval. Target steps were presented in blocks of either predictable (simple condition) or unpredictable (choice condition) amplitudes. The peak forces and the peaks of their time derivatives were analyzed to determine how subjects achieved accuracy under the different conditions and at different S-R intervals. The trajectories of responses produced in the simple condition were independent of the S-R interval. In contrast, when targets were presented in unpredictable order, the distribution of the peak forces of the subjects' responses depended on the S-R interval. At short S-R intervals (less than 125 ms), subjects made responses whose peak forces were distributed around the center of the range of target steps. These responses formed a unimodal, but broad distribution which was independent of actual target amplitude. With increasing S-R interval (greater than 125 ms), the distributions of peak forces gradually shifted toward the correct target amplitudes, with the means reaching the appropriate amplitudes at S-R intervals of 250-400 ms. At S-R intervals comparable to a reaction time, the range of peak forces was constricted to a similar extent as previously observed in a reaction time task (Hening et al. 1988). We found that the gradual improvement of accuracy was not achieved through changes in trajectory control: at all S-R intervals, subjects utilized a pulse-height control policy (Gordon and Ghez 1987a). Different peak forces were achieved by varying the rate of rise of force, while force rise time was held relatively invariant.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1986

Opioid responsiveness in patients with neuroleptic-induced akathisia.

Five patients with either acute or tardive neuroleptic-induced akathisia (5 weeks to 1 1/2 years duration) were videotaped before, during, and after a 2-week trial of propoxyphene (Darvon), 100 mg q.i.d., or acetaminophen (Tylenol) with 30 mg codeine, two tabs, q.i.d. Three "blinded" observers, experienced in movement disorders, rated the involuntary movements shown on the videotapes and agreed that, on opioids, all patients showed substantial to complete improvement of their stereotyped restless akathitic movements. Matching placebo was not beneficial. One patient who had improved on opioids was challenged with naloxone while on the opioids. There was a brief but severe reactivation of the akathisia. Our results suggest that opioids offer a selective therapy for patients with neuroleptic-induced akathisia and further suggest that the endogenous opiate system may be involved in patients with neuroleptic-induced akathisia.

Acetaminophen↗
PubMed1986

Dominantly inherited restless legs with myoclonus and periodic movements of sleep: a syndrome related to the endogenous opiates?

The restless legs syndrome is a sensory and motor disorder of evening, repose, and sleep. The cardinal features include (a) restlessness, which is frequently associated with (b) dysesthesias, (c) myoclonic jerks and other dyskinesias while awake, (d) periodic movements of sleep, and (e) sleep disturbances. We have recently had the opportunity to study two patients severely affected by this syndrome whose family histories are consistent with dominant inheritance. Both patients serendipitously discovered that their symptoms responded uniquely well to opiate medication. Both patients were studied extensively with electrophysiological and videotape monitoring, and their movements were characterized. In both patients, all elements of the syndrome responded to opiates, with marked relief of symptoms and without any significant side effects. The specific opiate antagonist naloxone blocked the therapeutic benefit of the opiates. Our findings support the involvement of the endogenous opiate system in the pathogenesis of restless legs and related dyskinesias and suggest that opiate therapy may be a potentially valuable treatment for this sometimes disabling syndrome.

Aged↗
PubMedDate not supplied

Opioid treatment of periodic movements in sleep in patients without restless legs.

Opioids may be a useful treatment for some patients with Periodic Movements of Sleep (PMS) and sleep disturbances. Four patients who had only idiopathic PMS and sleep disturbances but not Restless Legs Syndrome (RLS) were treated with various opioids. Two of the patients responded with a more than 98% decrease in the number of PMS per night of sleep and a doubling of the percentage of sleep period time spent in deep (Stages 3 and 4) sleep.

Aged↗