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PubMed1996

Lateralization of brain mechanisms underlying automatic and controlled forms of spatial orienting of attention.

Unilateral Spatial Neglect (USN) can be considered as a defect in spatial orienting of attention toward the half space contralateral to the damaged hemisphere. Since the classical work of Brain, W.R. Brain 64:224-272 (1941), several authors have emphasized that this defect is definitely more frequent and severe in patients with right brain damage, but the reason for this hemispheric asymmetry has remained controversial. Several investigations conducted with different experimental paradigms in different laboratories have shown that only automatic orienting of attention toward stimuli arising in the half space contralateral to the damaged hemisphere is disrupted in USN, whereas controlled, volitional orienting can be more or less completely spared. The hypothesis that at the level of the right hemisphere, spatial orienting of attention may be mainly prompted by automatic mechanisms may, therefore, be advanced. By contrast, the left hemisphere might play a leading role in mechanisms underlying volitional orienting of attention. According to this model, recovery from USN could be due to substitution of the lost automatic orienting mechanisms with the spread volitional orienting mechanisms subserved by the intact left hemisphere.

Attention↗

PubMed2005

The impact of the transmission dynamics of the HIV/AIDS epidemic on sexual behaviour: a new hypothesis to explain recent increases in risk taking-behaviour among men who have sex with men.

Increases in sexually transmitted infections and related high-risk behaviours have been reported among men who have sex with men (MSM) in industrialised countries when effective antiretroviral therapy against HIV infection has become widely available, in the mid-nineties. The reasons for these increases are not fully understood and often conflicting. Prevention fatigue, relapses to unsafe sex, as well as optimism toward the risk of developing AIDS among people living with HIV are not unique to the era of antiretroviral therapy (ART). This has led researchers to highlight the need to investigate other potential reasons that could explain the increase in high-risk taking following the ART introduction. We put forward the hypothesis that the change in the transmission dynamics of the HIV/AIDS epidemic before and after the introduction of ART has contributed to this change in high-risk behaviour. It is suggested that a decline in sexual risk activities has occurred at the population-level following the initial spread of the HIV/AIDS epidemic because AIDS mortality and severe morbidity disproportionately depleted the pool of high-risk taking individuals. As a result, non-volitional changes may have occurred at the individual-level over time because the depletion of this pool of high-risk individuals made it more difficult for the remaining high-risk taking individuals to find partners to engage in risky sex with. Following its introduction, ART has facilitated the differential replenishment of the pool of individuals willing to engage in high-risk taking behaviours because ART reduces AIDS mortality, and morbidity. Consequently, high-risk taking individuals who had previously reduced their level of risky sex non-volitionally (i.e., as a result of the reduced availability of high-risk partners) were able to resume their initial high-risk practices as the pool of high-risk taking individuals replenished over time. Thus, a fraction of the recently reported increase in high-risk sexual activities may be secondary to the fact that those MSM who were unable to engage in their desired high-risky sexual activities (because of reduced availability) are now able to revert to them as the availability of men willing to engage in risky sexual behaviours increases partly due to ART. Therefore, we suggest that a fraction of the changes in individual behaviour are non-volitional and can be explained by a change in "sexual partner availability" due to the transmission dynamics of HIV/AIDS before and after ART. The hypothesis is formulated and explained using simple social network diagrams and the Theory of Planned Behaviour. We also discuss the implication of this hypothesis for HIV prevention.

Acquired Immunodeficiency Syndrome↗

PubMed2005

Basic principles of control of breathing.

The metabolic demands of the body, including consumption of oxygen and removal of carbon dioxide, vary widely in health and disease. Ventilation must adjust to meet these demands and accommodate volitional and behavioral activities. Control of breathing depends on a complex and intricate feedback control system that integrates these automatic and volitional aspects of ventilation. Sensors, including chemoreceptors and lung volume receptors, relay information to a central controller located primarily in the medulla. The central controller integrates this information and determines the level of activation of the effectors (the respiratory motoneurons and muscles), which affects ventilation and gas exchange. Inputs from suprapontine structures, including the cerebral cortex, are also important in integrating volitional aspects of breathing into the control system.

Animals↗

PubMed2005

Central nervous system control of the laryngeal muscles in humans.

Laryngeal muscle control may vary for different functions such as: voice for speech communication, emotional expression during laughter and cry, breathing, swallowing, and cough. This review discusses the control of the human laryngeal muscles for some of these different functions. Sensori-motor aspects of laryngeal control have been studied by eliciting various laryngeal reflexes. The role of audition in learning and monitoring ongoing voice production for speech is well known; while the role of somatosensory feedback is less well understood. Reflexive control systems involving central pattern generators may contribute to swallowing, breathing and cough with greater cortical control during volitional tasks such as voice production for speech. Volitional control is much less well understood for each of these functions and likely involves the integration of cortical and subcortical circuits. The new frontier is the study of the central control of the laryngeal musculature for voice, swallowing and breathing and how volitional and reflexive control systems may interact in humans.

Brain↗

PubMed2004

Oculomotor control in asymptomatic and recently diagnosed individuals with the genetic marker for Huntington's disease.

We compared oculomotor control among individuals in the early stages of Huntington's disease (HD), with that of individuals who are presymptomatic HD gene carriers (PSGC) and nongene carriers (NGC). The oculomotor testing paradigm included both traditional tests and a novel experimental procedure to assess visual scanning. Traditional tests elicited saccades, pursuit and optokinetic nystagmus (OKN). HD patients demonstrated marked delay in the initiation of volitional saccades (anti-saccade and memory-guided saccades), a reduced number of correct volitional saccades, reduced velocity of saccades, and a decreased OKN gain. We also studied visual scanning while the participants completed the Digit Symbol Subscale of the Wechsler Adult Intelligence Survey-Revised (WAIS-R). The HD participants demonstrated an abnormal gaze strategy, which may be associated with attention and/or planning deficits. Differences between the PSGC and NGC groups were only observed for two measures: PSGC had a decreased number of memory-guided saccades and a subtle delay in the initiation of volitional saccades. Our results suggest that oculomotor measures are a sensitive biomarker in the early stage of HD and demonstrate that the combination of more traditional oculomotor tests with visual scanning tests is useful in the evaluation of visual performance.

Adult↗

PubMed1998

Aspiration in patients with acute stroke.

OBJECTIVES: To determine the frequency and clinical predictors of aspiration within 5 days of acute stroke. DESIGN: Case series. SETTING: Tertiary care center. PATIENTS: Consecutive stroke patients (n = 55) with new neurologic deficit evaluated within 5 days of acute stroke. MAIN OUTCOME MEASURES: Comparison of features identified on clinical swallowing and oromotor examinations and occurrence of aspiration (silent or overt) evident on videofluoroscopic swallow study (VSS). RESULTS: Aspiration occurred in 21 of 55 patients (38%). Whereas 7 of 21 patients (33%) aspirated overtly, 14 (67%) aspirated silently on VSS. Chi-square analyses revealed that dysphonia, dysarthria, abnormal gag reflex, abnormal volitional cough, cough after swallow, and voice change after swallow were significantly related to aspiration and were predictors of the subset of patients with silent aspiration. Logistic regression revealed that abnormal volitional cough and cough with swallow, in conjunction, predicted aspiration with 78% accuracy. CONCLUSIONS: Silent aspiration appears to be a significant problem in acute stroke patients because silent aspiration occurred in two thirds of the patients who aspirated. The prediction of patients at risk for aspiration was significantly improved by the presence of concurrent findings of abnormal volitional cough and cough with swallow on clinical examination.

Acute Disease↗

PubMed2001

The threshold trip duration for which recovery is no longer possible is associated with strength and reaction time.

The recovery of young adults from trips of increasing severity was studied. Our null hypothesis was that lower extremity strength, and reaction time, step time, step distance and step velocity measured in a volitional stepping task would not explain a significant portion of the variance in the magnitude of the threshold trip duration for which recovery is no longer possible. Ten males and 11 females (average age 26.8 and 28.4 years old, respectively) were subjected to trips of increasing duration until recovery was no longer possible with a single step. The average threshold trip duration for which subjects were no longer able to recover with a single step was 681+/-169ms. The threshold trip duration significantly increased as lower extremity strength increased and volitional reaction time decreased (multiple stepwise linear regression: R(2)=0.52, p=0.001). The other volitional step parameters and the subject characteristics were not significantly associated with the magnitude of the threshold trip duration. These results suggest that some trip-related falls may be due to slower reaction times and/or reduced lower extremity strengths.

Accidental Falls↗

PubMed2000

Acute partial paralysis alters perceptions of air hunger, work and effort at constant P(CO(2)) and V(E).

Breathing sensations of AIR HUNGER, WORK and EFFORT may depend on projections of central motor discharge (corollary discharge) to the forebrain. Source of motor drive (brainstem or cortex) may determine what is perceived. To test the effect of changing motor discharge at constant ventilation, we induced partial neuromuscular blockade during hypercapnic hyperpnea (31 + or - 9 L min(-1); PET(CO(2))=49 + or - 2 Torr) and during matched volitional hyperpnea (34 + or - 5 L min(-1); PET(CO(2))=41 + or - 1 Torr). Decline of vital capacity was similar between conditions (39%). Ventilation was unchanged with paralysis, indicating increased respiratory motor drive to maintain hyperpnea. Sensations were rated on a seven point ordinal scale. Median EFFORT and WORK increased 3-3.5 points with paralysis during both forms of hyperpnea (P<0.02, Wilcoxon signed rank). Median AIR HUNGER increased 2.5 points with paralysis during hypercapnic (P<0.02) but not during volitional hyperpnea. Data suggests that EFFORT and WORK arise from motor cortex activity (subjects reported engaging volitional control when paralyzed even during hypercapnia) and suggests that AIR HUNGER arises from medullary motor activity.

Adult↗

PubMed2001

Diaphragmatic function in patients with chronic left ventricular failure.

The aim of this paper is to evaluate the function of respiratory muscles in-patients with chronic moderate left ventricular failure (LVF), and its contribution to the pathophysiology of dyspnea and fatigue. We have studied 20 male patients with LVF, classes II and III of New York Heart Association (NYHA), mean age 66.9+/-10 years (GI) and 19 male aged-matched controls without cardiopulmonary disease mean age 64.6+/-8.4 years (GII). The evaluation included (a) methods derived from volitional manoeuvres, maximal inspiratory pressures at Functional Residual Capacity; maximal expiratory pressures at total lung capacity (TLC); nasal sniff; oesophageal sniff and transdiaphragmatic pressures; (b) methods derived from non-volitional manoeuvres, using bilateral cervical magnetic stimulation of the phrenic nerves, measuring the following twitch pressures (oesophageal, gastric and the transdiaphragmatic). With volitional manoeuvres we have not found statistically significant differences between the two groups: maximal expiratory pressures (cmH(2)O), GI 138+/-42; GII 152+/-40; P=NS and maximal inspiratory pressures (cmH(2)O), GI 74.1+/-22; GII 85+/-16; P=NS. However, these values were significantly lower than those obtained with sniff manoeuvres, nasal sniff (cmH(2)O), GI 95.6+/-22; GII 99.6+/-16; P=NS and oesophageal sniff (cmH(2)O), GI 96.2+/-20; GII 97.5+/-18; P=NS. There were no significant differences between nasal sniff and oesophageal sniff. Using cervical magnetic stimulation, we also didn't find a significant difference for transdiaphragmatic twitch between groups, but the contribution of the diaphragm to the transdiaphragmatic pressure was lower in patients with LVF since the oesophageal twitch was lower (cmH(2)O), GI 11.4+/-3.4; GII 16.3+/-6.8; P<0,004. In conclusion, the contribution of the diaphragm to total ventilation in-patients with moderate LVF is preserved. However, its capacity to generate negative intra-thoracic pressures is decreased since there is a significant decrease in oesophageal twitch. So, it seems that the diaphragm is the first inspiratory muscle to be affected in patients with moderate LVF.

Journal Article↗

PubMed2002

Action-state orientation and the self-regulation of eating behavior.

The present study examined the association between eating behavior and individual differences in volitional functioning as assessed by the Action Control Scale [Kuhl, J. (1994a). Action versus state orientation: psychometric properties of the Action-Control Scale (ACS-90). Volition and personality: action versus state orientation (pp. 47-56). Seattle: Hogrefe Huber]. Two hundred and nineteen undergraduate women completed measures of personality, affect, and eating behavior, which included the Action Control Scale (ACS) and the Three-Factor Eating Questionnaire [J. Psychosom. Res. 29 (1985) 71]. Hierarchical regression analyses that controlled for the influence of negative affect showed that scores on the Hesitation subscale of the ACS were positively associated with overeating and negatively associated with dietary restraint. These findings illustrate the importance of action-state orientation in the self-regulation of eating behavior and suggest the potential utility of targeting volitional skills in interventions to modify dysfunctional patterns of eating.

Journal Article↗

PubMed1999

Abnormalities of internally generated saccades in obsessive-compulsive disorder.

BACKGROUND: We aimed to utilize tests of saccadic function to investigate whether cognitive abnormalities in obsessive-compulsive disorder (OCD) arise from a dysfunction of inhibitory processes or whether they reflect a more general difficulty in guiding behaviour on the basis of an internal representation of task goal. METHODS: Twelve patients with OCD and 12 matched controls performed a visually-guided saccade task, a volitional prosaccade task and an antisaccade task. The latency and gain of saccades was compared between groups for the three saccade tasks. The number of antisaccade errors was also calculated and compared between groups. RESULTS: There was no difference for antisaccade error rates between the groups. The latency of visually guided saccades did not differ between groups, however the latency of both volitional prosaccades and antisaccades was significantly slower in the patients with OCD than in controls. The difference in latency between volitional prosacades and antisaccades, however, was equal between groups. CONCLUSIONS: These results suggest that patients with OCD have an abnormality in guiding behaviour on the basis of an internal representation of the task goal, rather than a problem with inhibiting reflexive behaviour.

Adult↗

PubMed2004

Attentional effects of counterpredictive gaze and arrow cues.

The authors used counterpredictive cues to examine reflexive and volitional orienting to eyes and arrows. Experiment 1 investigated the effects of eyes with a novel design that allowed for a comparison of gazed-at (cued) target locations and likely (predicted) target locations against baseline locations that were not cued and not predicted. Attention shifted reflexively to the cued location and volitionally to the predicted location, and these 2 forms of orienting overlapped in time. Experiment 2 discovered that another well-learned directional stimulus, an arrow, produced a different effect: Attention was shifted only volitionally to the predicted location. The authors suggest that because there is a neural architecture specialized for processing eyes, gaze-triggered attention is more strongly reflexive than orienting to arrows.

Adult↗

PubMed1981

Follow-up usage of the scott-craig Orthosis in paraplegia.

A survey of the usage of the Scott-Craig Orthosis among individuals with LI or above complete motor and sensory paraplegia is reported. Patients were grouped according to those without volitionally controlled abdominal musculature (C8-T5), those with volitionally controlled upper abdominal musculature (T6-T9), and those with all abdominal musculature under volitional control (T10-LI). The study was done in two phases. Phase I, done in 1976, consisted of a survey of 184 patients in this neurological grouping who received the Scott-craig Orthosis at Craig Hospital from 1 January 1964 through to 31 December 1975. Phase II was completed in December 1980. Sixty-three additional patients were surveyed who were braced from 1 January 1976 through to 31 December 1979. Long-term usage and some form of ambulation was found in 77 per cent of those surveyed.

Braces↗

PubMed1989

Exercise performance following intense, short-term ventilatory work.

Evidence exists to indicate that prolonged ventilatory work fatigues respiratory muscles and may limit exercise tolerance. However, the effects of short-duration, high-intensity ventilatory work on subsequent exercise remains in question. We tested the hypothesis that intense short-term volitional hyperpnea would result in respiratory muscle fatigue and would therefore hinder subsequent exercise tolerance. Pulmonary function was determined in ten healthy, male subjects before and after two constant load exercise tests to exhaustion on a cycle ergometer. Test 1 was a preliminary test to determine VO2max, peak exercise VE, and peak exercise power output. Test 2 was a constant load (85% peak power output) exercise test to exhaustion. Test 3 was identical to test 2 but was preceded by 10 min of volitional, isocapnic hyperpnea (85% of peak exercise V.E) at a controlled frequency and tidal volume. Pulmonary function measures (FVC, FEV1, FEV1/FVC, and peak flow) were not significantly (P less than 0.05) altered by the volitional hyperpnea. Ventilation and gas exchange variables (VO2, VE, f, end-tidal PO2 and PCO2, VE/VO2, VE/VCO2, %SaO2) during exercise and time to exhaustion were not significantly (P less than 0.05) different between treatments. These experiments failed to show any effect of short-term ventilatory work on pulmonary function or subsequent exercise performance.

Adult↗

PubMed2002

Fatigue decreases skilled tennis performance.

The aim of this study was to examine the effect of fatigue from maximal tennis hitting on skilled tennis performance. Eighteen senior county tennis players (9 males, 9 females) volunteered to participate in the study. Their mean (+/- s(mean)) age and body mass were as follows: males 20.7 +/- 0.9 years and 60.6 +/- 2.7 kg respectively, females 21.7 +/- 0.6 years and 71.5 +/- 1.8 kg respectively. The players undertook two performance tests, both against a tennis ball serving machine, on an indoor tennis surface: (1) a pre- and post-skill test of groundstrokes and service; (2) the Loughborough Intermittent Tennis Test (4 min work plus 40 s recovery) to volitional fatigue. Body mass decreased by 1.5% (P < 0.0001). Mean heart rates differed between rest, post-warm-up and all intermittent test values (P < 0.01), between the pre- and post-skill tests (P < 0.0001) and between bouts and recoveries (P < 0.01). Peak blood glucose and lactate concentrations were 5.9 mmol l(-1) (50% into the intermittent tennis test) and 9.6 +/- 0.9 mmol x l(-1) (25% into the test) respectively. Mean time to volitional fatigue was 35.4 +/- 4.6 min. Groundstroke hitting accuracy decreased by 69% from start to volitional fatigue in the intermittent test (P < 0.01). Service accuracy to the right court declined by 30% after the intermittent tennis test. The results of this study suggest that fatigue was accompanied by a decline in some but not all tennis skills.

Adult↗

PubMed2000

Response of prolonged flaccid paralysis to FNS rehabilitation techniques.

PURPOSE: The purpose of this study was to investigate the response of muscles with prolonged flaccid paralysis (a year after stroke) to two types of treatment: (1) functional neuromuscular stimulation (FNS) with surface electrodes; and (2) FNS with intramuscular (IM) electrodes (FNS-IM). A second purpose was to compare FNS-gait versus volitional gait (no FNS activation). METHOD: We used a single case study design; our patient was age 72, with flaccid paralysis of knee flexors and ankle dorsiflexors. RESULTS: Following four months of treatment with surface-stimulation, there was no change in muscle function or gait. Following treatment with FNS-IM, the patient regained partial volitional control of knee flexors and dorsiflexors; untreated muscles did not change. CONCLUSION: FNS-gait provided more normal knee and ankle dorsiflexion during swing phase versus volitional gait swing phase (no FNS activation).

Aged↗

PubMed1997

Assessment of corticospinal function in spinal cord injury using transcranial motor cortex stimulation: a review.

Other than clinical examination, few methods exist for assessing the functional condition of descending long tracts of the spinal cord in humans. This review covers neurophysiological examination of the corticospinal system using transcranial electrical and magnetic motor cortex stimulation. The neurophysiological basis for the motor evoked potentials (MEPs) and the differences between the two methods are discussed followed by a review of their use in individuals with spinal cord injury (SCI). Transcranial motor cortex stimulation is used to monitor descending spinal cord tract condition during spinal surgeries and could be useful for assessing central nervous system trauma, especially in the unconscious multitrauma patient. In the chronic phase of SCI, recordings of MEPs have enabled the estimation of central conduction times that relate to the condition of axons passing through the injured segment of the spinal cord. They were found to correlate well with clinical examination scores but as predictors of outcome, the reports have been mixed. The use of transcranial motor cortex stimulation to modify segmental reflexes and in combination with volitional attempts have also provided evidence of conduction across the lesion in paralyzed SCI subjects. However, MEPs can be absent in some SCI individuals who may be able to volitionally activate muscles below the level of the spinal cord lesion. Such findings are useful in elucidating the neural mechanisms underlying the performance of a volitional movement and may serve to guide and monitor the effects of future treatments for paralysis in SCI and other neurological disorders.

Animals↗

PubMed2005

Effects of a metabotropic, mglu5, glutamate receptor antagonist on ethanol consumption by genetic drinking rats.

AIMS: To compare the effect of an antagonist of the mGlu5 glutamate receptor, 2-methyl-6-(phenylethynyl)pyridine (MPEP) on a test for anxiety and on the volitional consumption of ethanol. METHODS: The test for anxiety was placement of a Sprague-Dawley rat for a 5 min observation period in an elevated plus-maze. Volitional consumption of ethanol in a two-choice paradigm was determined for male and female myers high ethanol-preferring rats after a 10-day 'step-up' test of 3-30% v/v ethanol vs water used to determine each rat's preferred concentration of ethanol. Each rat received a 4-day baseline period, 3-days of drug injection b.i.d., and a 4-day post-treatment period and then rotated to a different dose of drug or vehicle. RESULTS: The effects of MPEP on elevated plus-maze activity were not significant at doses up to 3.0 mg/kg subcutaneously 60 min. before observation. There was a dose-dependent, 0.3, 1.0, 3.0 mg/kg, decrease in consumption of preferred concentrations of ethanol, along with a decrease in the proportion of ethanol consumed to total fluids consumed. The 3.0 mg/kg b.i.d. dose of MPEP reduced consumption by 57%, proportion by 45%, and food intake by 10%. CONCLUSIONS: MPEP did not appear to have an anti-anxiety effect, but volitional drinking in a genetic model was reduced. The mGlu5 receptor may provide a target for drug action to reduce the consumption of ethanol.

Alcohol Deterrents↗