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PubMed2003

Neuroimaging evidence for cortical involvement in the preparation and in the act of swallowing.

This study employed whole head magnetoencephalography and synthetic aperture magnetometry to investigate the cortical topography of the preparation and the execution of volitional and reflexive water swallowing and of a simple tongue movement. Concerning movement execution, activation of the mid-lateral primary sensorimotor cortex was strongly lateralized to the left during volitional water swallowing, less strongly lateralized to the left during reflexive water swallowing, and not lateralized at all during tongue movement. In contrast, the preparation for both volitional water swallowing and tongue movement showed a bilateral activation of the primary sensorimotor cortex. No activation was seen prior to reflexive water swallowing. Activation of the left insula and frontal operculum was observed only during both the preparation and the execution of volitional water swallowing. These new findings suggest a left hemispheric dominance for the cortical control of swallowing in humans.

Adult↗
PubMed2001

Regulation of motor output between young and elderly subjects.

OBJECTIVES: Considerable information exists concerning the differences in motoneuron pool (MP) excitability between young and elderly subjects. A recent study demonstrated decreased heteronymous Ia facilitation with aging, suggesting increased presynaptic inhibition (PI) with increasing age as a mechanism for this change (Morita et al., Exp Brain Res 104 (1995) 167). It has been suggested that during voluntary movement, supraspinal, and possibly, segmental mechanisms (Hultborn et al., J Physiol 389 (1987) 757) modulate this inhibition. It is theorized that PI can modulate the recruitment gain of the MP during movement without altering the excitability of the motoneurons. Therefore, the purpose of this study was to examine the roles of PI and volitional volleys in modulating MP output in young and elderly subjects. METHODS: Twenty apparently healthy females participated in this study, 10 college aged (mean age, 22.4+/-2.8 years) and 10 independent, community dwelling elderly (mean age, 77.6+/-5.4 years). All subjects were tested in a semi-recumbent position. H-reflexes were elicited at rest, and at 10 and 20% of maximal voluntary contraction. To assess MP output, background electromyography (EMG) was monitored prior to stimulation. The stimulus intensity was adjusted during volitional contractions to ensure similar control reflexes (25% of the maximal motor response (M-max)) at each level of contraction. RESULTS: Control reflexes at each level of volitional contraction (rest, 10 and 20%) were similar for both groups. To assess PI and to estimate the extent to which a change in the H-reflex amplitude reflects a change in MP gating, the common peroneal nerve was stimulated at 1.5 times the motor threshold 100 ms prior to stimulation of the tibial nerve. Significantly greater PI was observed for the young subjects at rest (5 vs. 13% M-max). At both 10 and 20% levels of voluntary contraction, the conditioned reflex was significantly different from rest for the young subjects. The elderly subjects, in contrast, failed to modulate the conditioned reflex until the 20% of maximal voluntary contraction (MVC) condition. When examining the recruitment gain in the MP during the PI condition (H-reflex amplitude as a function of EMG levels), a significant group effect was observed, with the young subjects demonstrating significantly higher PI gain. CONCLUSIONS: These results indicate differential control of MP output (e.g. PI vs. volitional volleys) in young and elderly subjects.

Adult↗
PubMed2005

Canadian Association of Neuroscience Review: Respiratory control and behavior in humans: lessons from imaging and experiments of nature.

The purpose of this review is to demonstrate that respiration is a complex behavior comprising both brainstem autonomic control and supramedullary influences, including volition. Whereas some fundamental mechanisms had to be established using animal models, this review focuses on clinical cases and physiological studies in humans to illustrate normal and abnormal respiratory behavior. To summarize, central respiratory drive is generated in the rostroventrolateral medulla, and transmitted to both the upper airway and to the main and accessory respiratory muscles. Afferent feedback is provided from lung and muscle mechnoreceptors, peripheral carotid and aortic chemoreceptors, and multiple central chemoreceptors. Supramedullary regions, including cortex and subcortex, modulate or initiate breathing with volition, emotion and at the onset of exercise. Autonomic breathing control can be perturbed by brainstem pathology including space occupying lesions, compression, congenital central hypoventilation syndrome and sudden infant death syndrome. Sleep-wake states are important in regulating breathing. Thus, respiratory control abnormalities are most often evident during sleep, or during transition from sleep to wakefulness. Previously undiagnosed structural brainstem pathology may be revealed by abnormal breathing during sleep. Ondine's curse and 'the locked-in syndrome' serve to distinguish brainstem from supramedullary regulatory mechanisms in humans: The former comprises loss of autonomic respiratory control and requires volitional breathing for survival, and the latter entails loss of corticospinal or corticobulbar tracts required for volitional breathing, but preserves autonomic respiratory control.

Behavior↗
PubMed1991

Activity of wrist muscles elicited during imposed or voluntary movements about the elbow joint.

To examine the coordination of muscles during multijoint movement, we compared the response of wrist muscles to perturbations about the elbow joint with their activation during a volitional elbow movement. The purpose was to test the following two predictions: (a) Responses can occur in muscles not stretched by the perturbation, as has been reported for other multijoint systems; and (b) the motor pattern in response to a perturbation mimics an opposing volitional motor pattern across the two joints. We recorded the electromyographic (EMG) activity of elbow and wrist muscles as well as the flexion/extension motions at the elbow and wrist joints during individual trials that either involved a response to a torque perturbation that extended the elbow or required volitional elbow flexion. The results of this study confirmed that responses were elicited in the nonstretched wrist muscles when the elbow joint was perturbed. The same motor sequence of elbow and wrist flexors was present for both the volitional and perturbation task (with the forearm supinated), regardless of whether the wrist joint was immobilized or freely moving. The findings suggest that the nervous system relies on the purposeful coupling of elbow and wrist flexors to counter the inertial effects during the unrestricted voluntary movement, even though the coupling does not appear to be purposeful during the perturbation or with the wrist immobilized. The coupling of elbow and wrist flexors, however, was not rigidly fixed, as evidenced by muscle onsets that adapted over repeated perturbation trials and a reversal of the wrist muscle activated (wrist extensor) when the forearm was pronated. Hence, the coupling of muscle activities can be modified quantitatively when not beneficial and can be altered qualitatively with different initial configurations of the arm.

Journal Article↗
PubMed2000

Vestibulopathy and the age effects on protective stepping during unperturbed standing.

This study examined the prevalence of protective stepping and accompanying preparatory postural responses associated with lateral weight transfer (WT) while subjects attempted to sustain stationary standing. The subjects were 92 healthy young and older adults and persons with vestibular hypofunction. Force platform and whole-body-motion recordings were used to evaluate the prevalence of stepping and WT responses during stationary standing (eyes open or closed) using a semi-tandem foot position. WT components were also evaluated for volitionally requested step initiation, and as a function of support base configuration and direction of stepping among younger subjects. Only 10% of trials by subjects with bilateral vestibular hypofunction (BVH) during semi-tandem standing with eyes closed were completed without a step, while 31% of subjects with UVH, 69% of healthy elders, and all young healthy subjects were able to stand for the entire 7-sec trials. WT responses always preceded volitional steps from a standard feet-parallel orientation but occurred in only 13% of the spontaneous steps. The prevalence of WT was influenced by the direction of volitional stepping from semi-tandem standing, but not by the initial standing width. Spontaneous stepping to maintain standing balance is a naturally occurring and prevalent behavior among older adults and persons with vestibular hypofunction during tests of quasi-static standing. Differences between volitional and spontaneous step initiation involving the prevalence of preparatory lateral WT are a complex function of motor planning, mechanical constraints, and functional context.

Adult↗
PubMed1997

Musical hallucinations and musical imagery: prevalence and phenomenology in schizophrenic inpatients.

The discussion of auditory hallucinations in schizophrenia has traditionally focused on verbal auditory hallucinations, or 'voices'. Little attention, on the other hand, has been given to the phenomenon of musical hallucinations. In an effort to characterize the prevalence and phenomenology of musical hallucinations, 100 consecutive schizophrenic inpatients were examined for the presence of musical hallucinations and musical imagery. Sixteen patients responded positively, and were engaged in a more thorough interview. They were then divided into two groups: those with musical hallucinations, and those experiencing musical imagery. This determination was made based on the absence or presence, respectively, of volitional control, hypothesizing that lack of volitional control implies a true hallucinatory experience. When lack of volitional control was compared to the various other aspects of the experience, an association with religious content was demonstrated. Religious musical hallucinations also tended to be experienced as distressing, further supporting the hypothesis that the experience was hallucinatory rather than a product of volitional imagery. A selection of sample case vignettes is presented as well.

Adult↗
PubMed2005

Cognitive processes in saccade generation.

The analysis of saccades offers an opportunity to study a number of different cognitive processes, such as visuospatial attention, working memory, and volitional conflict. A study of saccades in patients with visuospatial hemineglect, who performed a visual search task, showed repeated fixations on targets previously discovered, yet they often failed to retain the information that a particular target had previously been discovered. High-resolution structural brain scanning showed that this abnormality was due either to a lesion in the right intraparietal sulcus or the right inferior frontal lobe. Detailed analysis of the scanpaths suggested that the former location was associated with an accumulating impairment in remapping target locations across saccades or impaired memory of previously inspected target locations, whereas the latter location was more consistent with a failure to inhibit responses to rightward locations. When combined with a spatial bias to the right, such deficits might explain why many neglect patients often reexamine rightward targets, at the expense of items to their left. The functions of the supplementary eye field (SEF), in the medial frontal lobe, in relation to saccade generation are controversial. A series of studies in a patient with a focal lesion of the right SEF has indicated an important role for the SEF in the rapid self-control of saccadic eye movements and in set-switching (i.e., implementing control in situations of response conflict when ongoing saccadic plans have to be changed rapidly), rather than monitoring errors. In a recent fMRI study of normal subjects, it was shown that the SEF is involved in implementing the resolution of any volitional conflict, whereas other presupplementary motor areas are involved in the generation of volitional plans and processing volitional conflict.

Brain Mapping↗
PubMed1995

Contribution of the respiratory muscles to the lactic acidosis of heavy exercise in COPD.

Patients with COPD usually are limited in their exercise tolerance by a limited ventilatory capacity. Lactic acidosis induced by exercise increases the stress on the ventilatory system due to CO2 generated by bicarbonate buffering and hydrogen ion stimulation. Patients with COPD are often observed to increase blood lactate levels at low levels of exercise. We wished to determine whether patients with COPD who experience lactic acidosis do so because of respiratory muscle production of lactate. Eight patients with moderate to severe COPD (FEV1 = 43.5 +/- 11.6% predicted) and 5 healthy subjects performed 10 min of moderate constant work rate exercise either breathing spontaneously or volitionally increasing their ventilation for 5 min to approximate the peak minute ventilation seen during incremental exercise. During volitional increased ventilation, 3% CO2 was added to the inspirate to prevent alkalosis and hypocapnia. In neither the healthy subjects nor the COPD group was the end-exercise lactate level significantly higher during volitional ventilation increase than during spontaneous ventilation. Further, in the COPD patients, the blood lactate levels during volitional ventilation increase were much lower than during maximal exercise (averaging 2.4 vs 5.3 mmol/L) despite similar ventilation levels (averaging 50 and 53 L/min). We conclude that it is unlikely that the respiratory muscles have an important influence on the blood lactate level elevation seen during maximal exercise in COPD patients.

Acidosis, Lactic↗
PubMed1988

The origin of the initial abrupt increase in ventilation at the onset of muscular exercise (phase 1) in man.

Ventilation and cardiac output in response to four different exercises, namely, volitional pedalling using a bicycle ergometer with a very mild (7 Watt) load, passive pedalling, electrically-induced isometric twitches of one leg, and voluntary twitches simulating the previous electrical twitches, were measured simultaneously during the transient phase from rest. Cardiac output was determined by automated impedance cardiography. A sudden increase in ventilation was observed immediately after the onset of the volitional and passive pedalling whereas cardiac output increased only gradually. Only a slight difference was observed between the cardio-ventilatory responses to volitional and passive exercises. Neither ventilation nor cardiac output changed significantly in response to volitional and electrical twitches of one leg. Conclusions were then drawn that the cardio-dynamic process could be ruled out as the origin of the initial ventilatory response, and instead, other neurogenic mechanisms mediated either centrally or peripherally, should be considered.

Adult↗
PubMed2001

VO2 slow component correlates with vastus lateralis de-oxygenation and blood lactate accumulation during running.

BACKGROUND: In the present study, vastus lateralis de-oxygenation was monitored contemporarily with VO2 changes along a severe constant intensity running exercise, after the 3rd min up to volitional exhaustion. Blood lactate accumulation was also measured before, during and after running. METHODS: Eleven male amateur soccer players volunteered for the study. Subjects mean age, height, and body weight were 22.9+/-2 yrs, 177.5+/-6.2 cm, 71.7+/-4 kg, respectively. Measurements were carried out during running on a treadmill. Ventilatory and gas exchange parameters were measured at the mouth on a breath-by-breath basis. For blood lactate concentration accumulation measurement, capillary blood samples were taken from the fingertip. The oxygenation of the vastus lateralis muscle were measured by a continuous wave NIRS portable instrument. By means of two pretests the onset of [La]b accumulation and its associated velocity (vOBLA), and the peak of oxygen uptake and its associated velocity (vVO2,peak) were assessed. The test consisted of running on the treadmill up to volitional exhaustion at a constant velocity corresponding to vOBLA plus 50% of the difference between vVO2,peak and vOBLA (v50%Delta). RESULTS: The principal finding of this study was that vastus lateralis de-oxygenation changes measured during running correlate with a) oxygen uptake changes between the 3rd min of exercise and the time corresponding to the subject's volitional exhaustion; b) blood lactate concentration increments measured at the 3rd and the 6th min of exercise and at the time corresponding to the subject's volitional exhaustion. CONCLUSIONS: In conclusion, the results of the present study support our hypothesis that the vastus lateralis de-oxygenation contributes consistently to the VO2 slow component development in running.

Adult↗
PubMed1965

ABDOMINAL ELECTROMYOGRAPHY DURING MICTURITION.

Electromyographic tracings during micturition were obtained from the abdominal muscles of volunteer men by means of silver cup electrodes. Electromyographic tracings of cough, strain and volitional and sphincter contraction were made before and after voiding on desire and on volition. While the EMG activity of cough and strain remain unchanged, that of volitional and sphincter contraction underwent various changes following both types of voiding. Before or at the onset of micturition on desire the EMG remained unchanged in ten of 14 subjects, but with cessation of micturition it remained unchanged in only seven subjects while it increased in the remaining seven. Before or at the onset of micturition on volition the EMG remained unchanged in seven of nine subjects, and with cessation of micturition it remained unchanged in eight of the nine subjects. Interruption of micturition increased the EMG activity of six among seven subjects, but resumption of micturition did not alter the EMG in five of the seven subjects. Great variations existed in regard to urinary volume and flow rate. It is proposed that there is an association of movements between the abdominal and pelvic floor muscles and that these movements are more conspicuous with cessation and interruption than with onset of physiological micturition.

Abdomen↗
PubMed2006

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise.

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac-]B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207+/-8 W, mean +/- SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20-28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3+/-2.4 and 168.3+/-7.0 l min(-1) (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9+/-6.8 l min(-1)), 3.46+/-0.20 and 3.83 +/- 0.20 l min(-1) (P<0.01), and 158.5+/-2.7 and 166.8+/-2.7 beats min(-1) (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac-]B increased from 3.7+/-0.2 to 4.7+/-0.3 mmol l(-1) (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac-]B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac-]B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.

Adult↗
PubMedDate not supplied

An EMG study of functional cortico-motoneuronal connections in humans.

We set out to decompose the EMG signal into its constituent motor unit action potential components to track motor unit firing rates with a high degree of accuracy and extract their average firing rate. We were able to show that this average firing rate tracks the subject's force trajectory from beginning to end. We propose that this average firing rate is a volitional control signal pointing to the existence of a 'volitional unit'. This volitional unit has to do with the projection of a group of functionally related cortico-motoneurons on a group of spinal motoneurons in the motoneuronal pool of a muscle. Our study of motor unit firing patterns during their steady state showed that spinal motoneurons respond to a descending central input in a Gaussian manner. We have further shown that the central drive itself, as represented by the average firing rate of the active motor units, also displays a Gaussian firing behavior. We have also described the existence of a 'translation factor', highly correlated to the motor unit size, which is unique to each spinal motoneuron and determines the motoneuronal response, and its resulting firing rate, to the descending inputs. As for force generation, we have shown that expressing the twitch force of a motor unit in a dynamic fashion using the 'electrotwitch' concept of firing rate x macro area, approximates motor unit force output better and accounts for firing rate related force changes more effectively than force estimates based on the mechanical twitch.

Adult↗
PubMed2002

Orienting attention in aging and Parkinson's disease: distinguishing modes of control.

Past research on attentional orienting and Parkinson's disease (PD) has been compromised because the experimental paradigms tended to confound different forms of orienting. We sought to overcome this by examining the attentional orienting of three distinct groups (PD-patients, age-matched controls, and young controls) on five different tasks, four of which isolated pure forms of orienting. On two covert orienting tasks PD patients oriented volitional (Experiment 1) and reflexive (Experiment 2) covert attention in a healthy and normal manner for their age. On two overt orienting tasks, PD patients were found to execute volitional eye movements that were prone to undershoot their target goal (Experiment 3), and reflexive eye movements that were unusually fast (Experiment 4). When required to perform an antisaccade task (Experiment 5), which combines reflexive and volitional modes of overt orienting, PD patients performed normally. This indicates that using a task which combines different modes of orienting creates a situation that is more than the sum of its parts. Together our study supports the thesis that it is crucial to isolate and investigate different modes of attentional control.

Aged↗
PubMed2003

Why are antisaccades slower than prosaccades? A novel finding using a new paradigm.

Eye movements away from a new object (antisaccades) are slower than towards it (prosaccades). This finding is assumed to reflect the fact that prosaccades to new objects are made reflexively, and that for antisaccades, reflexive eye movements have to be inhibited and antisaccades are generated volitionally. Experiment 1 investigated the relative contribution of saccade inhibition by comparing the latency difference between pro- and antisaccades obtained in the traditional blocked paradigm and in a new paradigm in which oculomotor inhibition across pro- and antisaccades was matched. When inhibition was placed on the oculomotor system, the latency difference between pro- and antisaccades was significantly reduced. Experiment 2 examined the contribution of volitional saccade programming and execution by requiring both pro- and antisaccades to be programmed volitionally. This manipulation did not decrease further the difference between pro- and antisaccades. It is thus concluded that oculomotor inhibition is the main factor leading to long antisaccade latency. The remaining difference is attributed to the reallocation of covert attention from the target location towards the opposite antisaccade location.

Adult↗
PubMed1999

Impairment of willed actions and use of advance information for movement preparation in schizophrenia.

OBJECTIVES: To assess willed actions in patients with schizophrenia using reaction time (RT) tasks that differ in the degree to which they involve volitionally controlled versus stimulus driven responses. METHODS: Ten patients diagnosed with schizophrenia and 13 normal controls of comparable age were tested. Subjects performed a visual simple RT (SRT), an uncued four choice reaction time (CRT), and a fully cued four choice RT task. A stimulus 1(S1)-stimulus 2(S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 (no warning signal or precue) 200, 800, 1600, or 3200 ms. RESULTS: The patients with schizophrenia had significantly slower RTs and movement times than normal subjects across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, fully cued CRTs were significantly faster than the uncued CRTs. However, the S1-S2 interval had a differential effect on CRTs in the two groups. For the normal subjects fully cued CRTs and SRTs were equivalent when S1-S2 intervals were 800 ms or longer. A similar pattern of effects was not seen in the patients with schizophrenia, for whom the fully cued CRT were unexpectedly equivalent to SRT for the 200 ms interval and expectedly for the 1600 ms S1-S2 interval, but not the 3200 or 800 ms intervals. CONCLUSIONS: Patients with schizophrenia were able to use advance information inherent in SRT or provided by the precue in fully cued CRT to speed up RT relative to uncued CRT. However, in the latter task, in which the volitional demands of preprogramming are higher since a different response has to be prepared on each trial, patients showed some unusual and inconsistent interval effects suggesting instability of attentional set. It is possible that future studies using RT tasks with higher volitional demands in patients with predominance of negative signs may disclose greater deficits in willed action in schizophrenia.

Adult↗
PubMed1977

[Insufficient excitation for speech in focal lesions of non-specific brain structures].

On the basis of a study of 150 patients with focal lesions of the mesencephalo-diencephalic brain areas the authors discuss speech disorders, appearing due to disturbances in the functions of the activating nonspecific systems. They indicate that these speech disorders are conditioned by an insufficiency of speech volition. However, in communicative important situations for the patient they can be overcome. In development of mesencephalodiencephalic pathology the syndrome of insufficient speech volition may be transmitted into a clinical picture of akinetic mutism. The problem of differentiation of insufficiency speech volition is being discussed in relation to lesions on different levels of the activizing nonspecific system and the accompanying drop of speech activity of the motor-aphatic and disarthric disorders.

Adult↗
PubMed1983

The anterior cingulate cortex and the phonatory control in monkey and man.

Electrical stimulation of the anterior cingulate cortex yields vocalization in the monkey. The elicited vocalizations seem to represent primary stimulus responses. Monkeys are not able to perform a vocal conditioning task after ablation of the anterior cingulate cortex. However, they can carry out a lever-pressing conditioning task following destruction of this area. It is hypothesized that the anterior cingulate cortex exerts the volitional control of species-specific vocalizations in monkey. The non-verbal emotional vocal utterances are considered to be the human homologue of monkey's vocalizations. Therefore, bilateral lesion of the anterior cingulate cortex in man should hamper the volitional control of emotional vocal utterances in man as it does in monkeys. One personal observation is reported where after a bilateral infarction of the anterior cingulate cortex the patient's voice showed a permanent lack of emotional expression. The anterior cingulate cortex seems to play the decisive role in the volitional verbalization of emotions.

Animals↗