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At least 415 records · Page 23Linked to original sources
PubMed2001

Event-related functional magnetic resonance imaging in Parkinson's disease before and after levodopa.

Event-related functional MRI (fMRI) was used to study blood oxygen level dependent cortical signal changes associated with volitional limb movements off and on levodopa in Parkinson's disease. Eight patients with early stage akinetic Parkinson's disease and eight healthy volunteers underwent three functional imaging runs (high speed echo planar imaging with 600 scans/run) while performing paced single joystick movements in a freely chosen direction every 7-15 s. The non-magnetic joystick was linked to a monitoring system for on-line registration of performance parameters along with timing of the pacing tones and fMRI-scan acquisition parameters. This allowed correlation of movement onset, i.e. event-onset, to scanning time. We repeated the scanning procedure in the Parkinson's disease patients when akinesia improved 30 min after oral levodopa. Compared with the control group, patients both off and on levodopa showed movement-related impaired activation in the rostral supplementary motor area and increased activation in primary motor cortex (M1) and the lateral premotor cortex bilaterally. Levodopa led to a relative normalization of the impaired activation in the mesial premotor cortex and decreased signal levels in M1, lateral premotor and superior parietal cortex. We conclude that levodopa improves impaired motor initiation in the supplementary motor area and decreases hyperfunction of lateral premotor and M1 associated with Parkinson's disease during simple volitional movements.

Aged↗
PubMed1992

The relation of high density lipoprotein cholesterol and its subfractions to apolipoprotein A-I and fasting triglycerides: the role of environmental factors. The Atherosclerosis Risk in Communities (ARIC) Study.

Cross-sectional analysis of four general representative populations of middle-aged adults in the United States in 1986-1989 provides estimates of the close relation of high density lipoprotein cholesterol (HDL cholesterol) to its major structural apolipoprotein (apolipoprotein A-I) and to fasting plasma triglyceride levels. HDL cholesterol differences of approximately 0.4 mg were associated with 1-mg differences in apolipoprotein A-I; differences of 20% in HDL cholesterol (reductions) were associated with triglyceride doublings. Variation in apolipoprotein A-I and triglyceride concentration together accounted for 66% of the population variance in HDL cholesterol. The uniformity of this pattern in the four race-sex groups studied suggests an important role of triglyceride-cholesterol transfer as a determinant of HDL cholesterol. The fundamental relations observed among HDL cholesterol, apolipoprotein A-I, and triglycerides were unaltered by levels of factors under personal volition. The volitional factors appeared to influence HDL cholesterol indirectly: Obesity and physical activity were affected primarily through their associations with triglycerides, and alcohol use and smoking through associations with apolipoprotein A-I. The association of alcohol use with elevated HDL cholesterol was attenuated in persons with greater body mass.

Aged↗
PubMed1993

Muscle fatigue: clinical implications for fatigue assessment and neuromuscular electrical stimulation.

Muscle fatigue can be defined as a decrease in the force-generating ability of a muscle that resulted from recent activity. Recent studies of muscle fatigue are reviewed that are relevant to two areas of interest to physical therapists: clinical assessment of muscle fatigue and neuromuscular electrical stimulation. Volitional and electrical tests have been used to quantify muscle fatigue. Several variations on each type of test are discussed, as are the possible sites in which fatigue might occur. The rate of fatigue during the therapeutic application of electrical stimulation of skeletal muscle is much greater than that seen during volitional contractions. Factors contributing to this phenomenon are examined. The unique requirements affecting how stimulus variables can be manipulated to minimize muscle fatigue in three specific therapeutic uses of neuromuscular electrical stimulation are addressed.

Electric Stimulation↗
PubMed1990

The alien hand sign. Localization, lateralization and recovery.

The alien hand sign was first described by Brion and Jedynak as a "feeling of estrangement between the patient and one of his hands." The affected hand frequently shows a grasp reflex and an instinctive grasp reaction as well as elements of what Denny-Brown referred to as a "magnetic apraxia" associated with frontal lobe damage. Most notably, however, the affected hand is observed to perform apparently purposive behaviors that are perceived as being outside the volitional control of the patient. The patients interpret the behavior of their own affected limb as being controlled by an external agent. They do not feel that they are initiating or controlling the behavior of the hand and often express dismay at the hand's "extravolitional" activity. The patients attempt to control behavior of the alien hand with the unimpaired hand by forcibly restraining the affected limb, an act that may be termed "self-restriction." In this paper, we report an additional four cases of alien hand sign in right-handed subjects: two involving the right hand and two involving the left hand. In each case, the clinical findings were associated with extensive unilateral damage of the medial frontal cortex of the hemisphere contralateral to the affected hand. Furthermore, the alien movement gradually disappears over the course of 6-12 months after the stroke. These clinical case studies are presented and discussed in the context of the "dual premotoer systems hypothesis," an anatomicophysiological model that proposes that action is organized by two separate but interactive premotor brain systems corresponding to evolutionarily defined medial and lateral cortical moieties. It is hypothesized that the alien mode behavior results from unconstrained activity of the lateral premotor system in the damaged hemisphere. The residual volitional control in the limb occurs through the activity of the intact medial premotor system of the ipsilateral hemisphere. Recovery may occur through extension of these ipsilateral control mechanisms by compensatory changes in subcortical systems controlling hemispheric activation associated with adaptive behavior. This observation may be important in understanding mechanisms involved in motor recovery after stroke.

Aged↗
PubMedDate not supplied

Correlation of motor control in the supine position and assistive device used for ambulation in chronic incomplete spinal cord-injured persons.

Neurocontrol of movement after spinal cord injury (SCI) is often spared, but few studies have investigated the chronic incomplete SCI patient. Multichannel surface electromyography (SEMG) can describe characteristics of neurocontrol during a series of volitional and reflex events. The relationship of these neurocontrol characteristics to clinical function is incompletely described. This study, retrospectively, evaluated the relationship between neurocontrol patterns evoked by lower limb movement in the supine position and the assistive device used for ambulation in chronic, incomplete SCI persons. The records of 15 neurologically healthy (9 male, 6 female) and 36 incomplete SCI persons (27 male, 9 female) (C2-T10) were used. SEMG was recorded from both quadriceps, adductors, hamstrings, anterior tibialis and triceps surae muscles and displayed on a stripchart for analysis. SEMG patterns of activity recorded in the supine position during volitional, unilateral, multijoint (hip and knee flexion and extension) movement attempts were characterized, divided into seven groups and compared with the subjects' self-selected ambulation device (independent, cane, crutches, walker or nonambulatory). The neurocontrol patterns recorded in the supine position correlated well with the SCI subjects ambulatory assistive device. Marked decreases in motor unit output and/or loss of motor organization were found in the nonambulatory group. Coactivation of proximal muscles, poor timing of muscle activity and radiation of activity into contralateral muscles were also noted in subjects who required a walker or crutches. To a lesser degree, abnormal motor patterns were also noted in subjects who ambulated with a cane or independently.

Adult↗
PubMedDate not supplied

Giant repeater F-wave in patients with anterior horn cell disorders. Role of motor unit size.

Conventional F-wave responses as well as single motor unit F-wave responses together with the volitionally recruited motor unit action potentials (MUAP) were studied in hand and feet muscles of 10 healthy subjects and 32 patients with anterior horn cell disorders. The amplitude of the largest F-wave (Fl) was significantly greater in the affected patients compared with healthy subjects. Giant repeater F-wave responses "up to 4 mV" were recorded in muscles having volitionally recruited giant MUAPs. Although, the group mean percentage of motor unit F-wave responses per stimulation in all tested orthodromic MUAPs was significantly decreased in amyotrophic lateral sclerosis patients, the group mean percentage of motor unit F-wave responses per stimulation in all tested orthodromic MUAPs that gave motor unit F-wave response was significantly increased compared with healthy subjects. The responding orthodromic MUAP gave identical motor unit F-wave response, even for complex polyphasic units. Enhanced monosynaptic (H-) reflex, proximal axon reflex (A-wave), and repetitive muscle response as possible explanations for the giant F-wave responses could be discounted. The electrophysiologic behavior of the giant late responses described here fits well with the criteria of F-waves modulated by newly formed distal (and or proximal) axonal branching.

Aged↗
PubMed2002

Motor function improvement following intrathecal baclofen pump placement in a patient with locked-in syndrome.

We describe a patient with locked-in syndrome who had minimal volitional motor function and severe spasticity in all four extremities. The patient showed a significant improvement in volitional motor function following intrathecal baclofen pump therapy to control spasticity. This case study suggests that intrathecal baclofen pump therapy might improve motor function in select patients with locked-in syndrome.

Adult↗
PubMed1999

Prenatal cocaine and neuromotor outcome at four months: effect of duration of exposure.

The effect of prenatal cocaine exposure on the motor development of full-term infants was examined in a prospective study, controlling for maternal characteristics and exposure to other substances. Intrauterine cocaine exposure was determined at birth by maternal self-report and was verified by hair analysis. At 4 months, 120 cocaine-exposed (COC) and 186 non-cocaine-exposed (NON-COC) infants were assessed by blinded examiners using a standard evaluation of neuromotor function, the Movement Assessment of Infants (MAI). Relative to NON-COC infants, COC infants had significantly higher full-scale MAI total risk scores after adjusting for covariates (p = .05). Infants exposed through the third trimester of pregnancy (n = 48) had higher MAI scores for both total risk (p = .02) and Volitional Movement (p = .01), and when compared with infants exposed only within the first two trimesters (n = 72), they had significantly more deficits in Volitional Movement (p = .03). Although MAI scores for the majority of exposed infants were within the normal range, infants exposed through the third trimester were at significantly increased risk for motor dysfunction (relative risk = 1.6; 95% confidence interval = 1.1, 2.8). Intrauterine cocaine exposure had an adverse effect on infant motor development after the neonatal period; this association was related to the timing and duration of gestational exposure. Further study is needed to evaluate the long-term clinical implications of neuromotor abnormalities in prenatally exposed infants.

Adult↗
PubMed1998

Postexercise potentiation of the H-reflex in humans.

UNLABELLED: Post-muscle activation effects on segmental reflexes reveal divergent results dependent upon the manner in which the muscle is activated. Electrically activating triceps surae invokes a potentiation of the Achilles' tendon reflex and the soleus (S) H-reflex termed posttetanic potentiation. In contrast, brief volitional activation produces a subsequent potentiation of tendon reflexes, whereas H-reflexes become depressed. PURPOSE: The present investigation explored the effect of an intense bout of volitional resistance exercise on the S and lateral gastrocnemius (LG) H-reflexes to determine if a potentiation of the H-reflex could be induced with physiological stimuli. METHODS: LG and S H-reflexes were obtained from 10 college age men and women before and after a vigorous bout (eight sets of 10 repetitions) of concentric-eccentric triceps surae exercise. RESULTS: Every subject displayed an initial depression of the LG (P < 0.01) and S H-reflex (P < 0.05) immediately postexercise, consistent with postactivation depression. As a group, there was a significant (P > 0.01) potentiation of the LG H/M ratio following the depression. Five of 10 subjects demonstrated this potentiation, which often lasted 10 min postexercise. The other five subjects displayed a longer and more profound early depression followed by a return to control levels. CONCLUSION: The data suggest that at least two overlapping processes are occurring, a brief depression followed by or superimposed over a longer lasting potentiation. Possible neural mechanisms and implications to strength training are discussed.

Adult↗
PubMed1998

Trunk muscle co-contraction increases during fatiguing, isometric, lateral bend exertions. Possible implications for spine stability.

STUDY DESIGN: Surface electromyographic activities were recorded from bilateral trunk muscles as test participants maintained a 50% maximum, voluntary, isometric, lateral bend contraction to volitional exhaustion. OBJECTIVES: To challenge the trunk with a prolonged lateral bend task and observe the responses of the agonist and antagonist muscles to the resulting fatigue. SUMMARY OF BACKGROUND DATA: Lateral bend exertions of the trunk have been identified as a risk factor for injury to spine tissues. However, little is known about the response of spine muscles to fatigue and the subsequent implications for spine stability, joint loading, and tissue injury. Surface electromyography provides a window on muscle loading and progressive fatigue. METHODS: Eleven male participants performed a set of maximum lateral bend exertions at the start of the trial, then maintained an upright standing posture while resisting 50% of the maximum moment until volitional exhaustion, then performed another set of maximum contractions. All contractions were isometric. Measurements were made, throughout each contraction, of the lateral bend moment and abdominal and trunk extensor electromyographic activities at six bilateral surface electromyography sites. Electromyographic amplitude and mean power frequency were calculated with 500-millisecond segments recorded serially every 800 milliseconds. Mean values were calculated with data from the first and last 5% of the trial durations. Statistics determined if fatigue had a significant effect on maximum moment and the electromyographic statistics for each muscle site. RESULTS: Fatigue resulted in a significant decrease in maximum lateral bend moment and increase in moment variability. Decreases in mean power frequency, indicating fatigue, were observed in three agonists (the trunk extensors) and one antagonist muscle. Unfatigued agonist electromyographic amplitudes correlated well with the mechanical advantage of muscles to generate lateral bend moments. Unfatigued antagonist activities were low except for the thoracic erector spinae. The agonists and antagonists demonstrated average increases of 17% and 8%, respectively, when pooled across muscles. Much of this change was predicted to have been associated with increases in co-contracting muscle forces. CONCLUSIONS: The trunk responded to a prolonged, lateral bend contraction by increasing co-contraction as agonist trunk muscles fatigued. It was proposed that the fatigue compromised neural coordination and that the co-contraction served to maintain spine stability.

Adult↗
PubMed2006

In vivo erector spinae muscle blood volume and oxygenation measures during repetitive incremental lifting and lowering in chronic low back pain participants.

STUDY DESIGN: A case control study. OBJECTIVES: Using metabolic gas analysis and near infrared spectroscopy, a comparison was made between healthy controls and chronic low back pain (LBP) participants on cardiorespiratory, erector spinae muscle blood volume, and oxygenation responses, and these variables were used to determine factors that best predict peak oxygen consumption (VO2peak). SUMMARY OF BACKGROUND DATA: To date, it is unknown how the cardiorespiratory and erector spinae muscles of chronic LBP persons respond to repetitive incremental lifting and lowering. With the advent of near infrared spectroscopy technology, it is now possible to noninvasively examine erector spinae muscle oxygen supply and utilization in vivo. Thus, by using metabolic gas analysis and near infrared spectroscopy technology simultaneously, it is now possible to compare the cardiorespiratory and erector spinae muscle responses of chronic LBP participants to that of healthy controls (no history of LBP) during incremental work to volitional fatigue. METHODS: Thirty-four participants with chronic LBP and 34 healthy controls completed the repetitive incremental lifting and lowering (2.25 kg x min) protocol from floor to table (height 76 cm) at 10 lifts . min to voluntary fatigue. RESULTS: The healthy controls had significantly greater VO2peak (mL x kg x min) and VO2peak (mL x kgLBM x min), peak mass lifted, test duration, and breathing frequency. Furthermore, healthy controls showed significantly greater change in muscle oxygenation and faster one-half recovery times. Multiple regression analysis indicated that approximately 97% of the variance in absolute VO2peak was predicted by cardiorespiratory variables in both groups, while muscle oxygenation aided in predicting VO2peak relative in the LBP participants. CONCLUSIONS: The results indicated that the chronic LBP participants demonstrated a reduced cardiorespiratory and erector spinae muscle response during repetitive incremental lifting and lowering to volitional fatigue as compared to the healthy controls.

Adolescent↗
PubMed2005

Effect of ice surface size on collision rates and head impacts at the World Junior Hockey Championships, 2002 to 2004.

OBJECTIVE: To determine if collision rates and head impacts in elite junior hockey differed between games played on the small North American ice surface (85 ft wide), an intermediate-size Finnish ice surface (94 ft wide), and the large standard international ice surface (100 ft wide). DESIGN: Videotape analysis of all games involving Team Canada from the 2002 (large ice, Czech Republic), 2003 (small ice, Canada), and 2004 (intermediate ice, Finland) World Junior Championships. All collisions were counted and separated into various categories (volitional player/player bodychecks, into boards or open ice, plus accidental/incidental player/boards, player/ice, head/stick, head/puck). Further subdivisions included collisions involving the head directly or indirectly and notably severe head impacts. RESULTS: Small, intermediate, and large ice surface mean collisions/game, respectively, were 295, 258, 222, total collisions; 251, 220, 181, volitional bodychecks; 126, 115, 88, into boards; 125, 106, 93, open ice; 71, 52, 44, total head; 44, 36, 30, indirect head; 26, 16, 13, direct head; and 1.3, 0.5, 0.3, severe head (P < 0.05 for small-intermediate ice and intermediate-large ice differences in total collisions; P < 0.005 for small-large ice difference; P < 0.05 for small-intermediate ice differences in head impacts; P < 0.01 for small-large ice differences in total and severe head impacts). CONCLUSIONS: There is a significant inverse correlation between ice size and collision rates in elite hockey, including direct, indirect, and severe head impacts. These findings suggest that uniform usage of the larger international rinks could reduce the risk of injury, and specifically, concussions in elite hockey by decreasing the occurrence of collisions and head impacts.

Brain Concussion↗
PubMed1998

Attention, self-regulation and consciousness.

Consciousness has many aspects. These include awareness of the world, feelings of control over one's behaviour and mental state (volition), and the notion of continuing self. Focal (executive) attention is used to control details of our awareness and is thus closely related to volition. Experiments suggest an integrated network of neural areas involved in executive attention. This network is associated with our voluntary ability to select among competing items, to correct error and to regulate our emotions. Recent neuroimaging studies suggest that these various functions involve separate areas of the anterior cingulate. We have adopted a strategy of using marker tasks, shown to activate the brain area by imaging studies, as a means of tracing the development of attentional networks. Executive attention appears to develop first to regulate distress during the first year of life. During later childhood the ability to regulate conflict among competing stimuli builds upon the earlier cingulate anatomy to provide a means of cognitive control. During childhood the activation of cingulate structures relates both to the child's success on laboratory tasks involving conflict and to parental reports of self-regulation and emotional control. These studies indicate a start in understanding the anatomy, circuitry and development of executive attention networks that serve to regulate both cognition and emotion.

Adult↗
PubMed1989

A multichannel FES system for the restoration of motor functions in high spinal cord injury patients: a respiration-controlled system for multijoint upper extremity.

A multichannel functional electrical stimulation (FES) system for the restoration of quadriplegic upper extremity function is described. The system is composed of a personal computer NEC PC-8801mkII, peripheral electronic circuits, CRT display and respiratory sensors for volitional control by the patient, and percutaneous electrodes. A C4 quadriplegic patient could drink canned tea by herself by using this FES system. Distinct features of the system are as follows: 1) Versatile volitional control was realized by controlling the memory allocation of the stored stimulation data by voluntary respiratory signals. 2) Sophisticated fine control of the fingers, wrists, and elbow was realized by creating the multichannel stimulation data from recorded myoelectric activities of normal subjects during movements of the upper limb.

Arm↗
PubMed1998

Postural after-contractions in man attributed to muscle spindle thixotropy.

1. It is an old observation that non-volitional arm abduction movements accompanied by a sensation of arm lightness often occur as an after-effect following forceful voluntary arm abductor contractions against a restraint. In the present study we have tested the hypothesis that such non-volitional, so-called 'postural after-contractions' are tonic reflex responses to an enhanced resting discharge in primary muscle spindle afferents which in turn is a consequence of thixotropy-dependent enhanced stiffness of intrafusal muscle fibres. 2. Results obtained in ten volunteers show that the arm abductor after-contraction phenomenon in man is most readily evoked by a type of conditioning procedure which in various respects mimics the procedure proven in animal experiments to be particularly effective in producing thixotropy-dependent excitation of primary spindle endings. 3. It is also shown that changes in arm abductor intramuscular temperature affect the strength of the after-contractions in a direction predicted by the thixotropy hypothesis. 4. Attention is drawn to several similarities between the after-contraction phenomenon with accompanying sensory illusions and the tonic reflex responses and illusions that can be induced when primary spindle endings are excited by muscle vibration. 5. The results support our hypothesis that postural after-contractions are induced by activity in primary muscle spindle afferents as a consequence of thixotropic properties of intrafusal muscle fibres. Central excitability changes following the conditioning voluntary effort may contribute to the phenomenon.

Adult↗
PubMed2001

Identification of higher brain centres that may encode the cardiorespiratory response to exercise in humans.

1. Positron emission tomography (PET) was used to identify the neuroanatomical correlates underlying 'central command' during imagination of exercise under hypnosis, in order to uncouple central command from peripheral feedback. 2. Three cognitive conditions were used: condition I, imagination of freewheeling downhill on a bicycle (no change in heart rate, HR, or ventilation, V(I)): condition II, imagination of exercise, cycling uphill (increased HR by 12 % and V(I) by 30 % of the actual exercise response): condition III, volitionally driven hyperventilation to match that achieved in condition II (no change in HR). 3. Subtraction methodology created contrast A (II minus I) highlighting cerebral areas involved in the imagination of exercise and contrast B (III minus I) highlighting areas activated in the direct volitional control of breathing (n = 4 for both; 8 scans per subject). End-tidal P(CO(2)) (P(ET,CO(2))) was held constant throughout PET scanning. 4. In contrast A, significant activations were seen in the right dorso-lateral prefrontal cortex, supplementary motor areas (SMA), the right premotor area (PMA), superolateral sensorimotor areas, thalamus, and bilaterally in the cerebellum. In contrast B, significant activations were present in the SMA and in lateral sensorimotor cortical areas. The SMA/PMA, dorso-lateral prefrontal cortex and the cerebellum are concerned with volitional/motor control, including that of the respiratory muscles. 5. The neuroanatomical areas activated suggest that a significant component of the respiratory response to 'exercise', in the absence of both movement feedback and an increase in CO(2) production, can be generated by what appears to be a behavioural response.

Adult↗
PubMed2006

The antisaccade task as a research tool in psychopathology: a critical review.

The antisaccade task is a measure of volitional control of behavior sensitive to fronto-striatal dysfunction. Here we outline important issues concerning antisaccade methodology, consider recent evidence of the cognitive processes and neural mechanisms involved in task performance, and review how the task has been applied to study psychopathology. We conclude that the task yields reliable and sensitive measures of the processes involved in resolving the conflict between volitional and reflexive behavioral responses, a key cognitive deficit relevant to a number of neuropsychiatric conditions. Additionally, antisaccade deficits may reflect genetic liability for schizophrenia. Finally, the ease and accuracy with which the task can be administered, combined with its sensitivity to fronto-striatal dysfunction and the availability of suitable control conditions, may make it a useful benchmark tool for studies of potential cognitive enhancers.

Humans↗
PubMed1994

The utility of an admission assessment to predict in-hospital nutrient intake.

OBJECTIVE: To determine if pre-complication nutrient intake can be predicted based on an admission assessment. DESIGN: Survey (cross-sectional study). SETTING: Geriatric Rehabilitation Unit (GRU) of a Veterans Administration hospital. PATIENTS: Three-hundred-twelve randomly selected admissions to the GRU. MEASUREMENTS: At admission, each patient completed a comprehensive medical, neuropsychological, functional, and nutritional assessment. While remaining hospitalized, each subject was monitored on a daily basis for the development of complications. Complete calorie counts were obtained at least every other day, and the average pre-complication daily volitional nutrient intake was expressed as a percent of predicted requirements as determined using the Harris-Benedict equation. RESULTS: Based on a stepwise linear regression analysis, the strongest predictor of pre-complication volitional intake was the first day calorie count, followed by waist circumference, the percent of weight lost in the 6 months prior to admission, supra-iliac skinfold thickness, and admission Katz ADL score. The model R2 = 0.66. CONCLUSIONS: It is possible to predict pre-complication nutrient intake with a fair degree of accuracy based on an admission assessment, which includes a 1-day calorie count.

Activities of Daily Living↗