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Biomedical subjects

A van Boxtel

Publications and source records attributed to A van Boxtel.

At least 19 recordsLinked to original sources
PubMed2002

Pericranial muscular, respiratory, and heart rate components of the orienting response.

We have earlier found that voluntary attention to weak auditory stimuli induces inhibition of respiration, heart rate, and electromyographic (EMG) activity of masticatory and lower facial muscles and that these responses lower the auditory threshold for low-frequency sounds. In the current study, we examined whether this inhibitory response pattern also occurs during involuntary orienting to novel, nonsignal sounds. Environmental sounds of low intensity were presented unexpectedly during the performance of a reading task. Orienting responses (ORs) were elicited as indicated by heart rate deceleration and skin conductance responses. Inhibitory respiratory and pericranial EMG responses appeared to be intrinsic components of the OR. Together with the autonomic responses, they habituated when a nonsignal auditory stimulus was repeatedly presented. Our results also suggest that eye and pinna movements occurred toward the sound source. The results of the current study are consistent with the hypothesis of Sokolov (1963) that the primary function of the OR is enhancement of sensory sensitivity.

Acoustic Stimulation↗
PubMed2001

Differences in autonomic physiological responses between good and poor inductive reasoners.

We investigated individual- and task-related differences in autonomic physiological responses induced by time limited figural and verbal inductive reasoning tasks. In a group of 52 participants, the percentage of correctly responded task items was evaluated together with nine different autonomic physiological response measures and respiration rate (RR). Weighted multidimensional scaling analyses of the physiological responses revealed three underlying dimensions, primarily characterized by RR, parasympathetic, and sympathetic activity. RR and sympathetic activity appeared to be relatively more important response dimensions for poor reasoners, whereas parasympathetic responsivity was relatively more important for good reasoners. These results suggest that poor reasoners showed higher levels of cognitive processing intensity than good reasoners. Furthermore, for the good reasoners, the dimension of sympathetic activity was relatively more important during the figural than during the verbal reasoning task, which was explained in terms of hemispheric lateralization in autonomic function.

Adult↗
PubMed2001

Optimal signal bandwidth for the recording of surface EMG activity of facial, jaw, oral, and neck muscles.

Spontaneous pericranial electromyographic (EMG) activity is generally small and is contaminated by strong low-frequency artifacts. High-pass filtering should suppress artifacts but affect EMG signal power only minimally. In 24 subjects who performed a warned simple reaction time task, the optimal high-pass cut-off frequency was examined for nine different pericranial muscles. From four experimental conditions (visual and auditory reaction signals combined with hand and foot responses), 1-min EMG recordings were selected (bandwidth: 0.4-512 Hz) and divided into 60 1-s data segments. These segments were high-pass filtered, the -3-dB cut-off frequency varying from 5 to 90 Hz, and subjected to power spectral analysis. Optimal high-pass filter frequencies were determined for the mean power spectra based on visual estimation or comparison with a theoretical spectrum of the artifact-free EMG signal. The optimal frequencies for the different muscles varied between 15 and 25 Hz and were not influenced by stimulus or response modality. For all muscles, a low-pass filter frequency between 400 and 500 Hz was appropriate.

Adult↗
PubMed2001

Inhibition of pericranial muscle activity, respiration, and heart rate enhances auditory sensitivity.

We investigated whether previously observed inhibition of pericranial electromyographic (EMG) activity, respiration, and heart rate during sensory intake processes improves auditory sensitivity. Participants had to detect weak auditory stimuli. We found that EMG activity in masticatory and lower facial muscles, respiration, and heart rate were more strongly inhibited when stimulus intensity was gradually lowered to threshold level whereas EMG of upper facial muscles progressively increased. Detection of near-threshold stimuli was inversely related to prestimulus EMG levels in masticatory and lower facial muscles. In two additional experiments, it was investigated whether steady, voluntary contractions negatively influence auditory sensitivity. As expected, contraction of zygomaticus produced an increase in auditory threshold in comparison with contraction of corrugator or first dorsal interosseus. It is concluded that attention to external stimuli is accompanied by quieting of those somatic activities that produce internal noise or are accompanied by impaired middle ear transmission of auditory stimuli.

Adolescent↗
PubMed1998

Optimal EMG signal bandwidth and interelectrode distance for the recording of acoustic, electrocutaneous, and photic blink reflexes.

The bandwidth for the recording of the orbicularis oculi blink reflex electromyogram (EMG) response is optimal when low-frequency artifacts, such as motion artifacts and cross-talk from other muscles, are maximally suppressed, whereas true EMG signal power is maximally retained. The optimal bandwidth was investigated for acoustic, electrocutaneous, and photic blink reflexes. Reflexes were recorded with varying bandwidth and interelectrode distances of 12 and 36 mm. Power spectra of the EMG signals were calculated and compared with a theoretical spectrum of the uncontaminated EMG signal. For both electrode distances, the optimal bandwidth was on the average 28-500 Hz for acoustic and electrocutaneous blink reflexes and 12-500 Hz for photic blinks. Using photic stimuli, however, a high-pass filter frequency larger than 12 Hz (probably at least 30 Hz) in combination with occlusion of the eye will be necessary to avoid influences of retinal potentials. Given the optimal bandwidth, a larger electrode spacing may be expected to moderately improve the detectability of small blinks in all stimulus conditions.

Acoustic Stimulation↗
PubMed1996

Anticipatory EMG responses of pericranial muscles in relation to heart rate during a warned simple reaction time task.

Obrist's cardiac-somatic coupling hypothesis predicts a widespread inhibition of heart rate and task-irrelevant muscle activity during expectancy situations. This hypothesis was tested by measuring heart rate and pericranial electromyographic (EMG) activity during a warned simple reaction time task with visual or auditory reaction signals and hand or foot responses. In each of three groups of 24 participants, EMG activity of three different facial, masticatory, or neck muscles was recorded. During the warning interval preceding the presentation of the reaction signal, masticatory and lower facial muscles predominantly showed a gradual inhibition in activity concomitant with heart rate deceleration. In contrast, two upper facial muscles showed increasing activity. Pericranial EMG responses were little affected by reaction signal modality and were independent of responding limb. Greater heart rate deceleration was associated with greater inhibition and weaker facilitation of EMG responses. The results suggest a functional role of inhibitory EMG responses in increasing the perceptual sensitivity to expected signals.

Adult↗
PubMed1995

Motor function in a patient with bilateral lesions of the globus pallidus.

This study describes the long-term deficits of a patient who, after a toxic encephalopathy, sustained extensive bilateral damage to both segments of the globus pallidus (GP) and the right substantia nigra (SN). There were no signs of lesions of the pyramidal tracts or of other motor structures. The most obvious deficits were an abnormal gait with an exaggerated knee extension and a tendency to fall slowly, especially when pushed backward. In contrast, Romberg's test on an unstable platform was normal, as were long-latency leg reflexes induced by perturbations. Inadequate anticipatory and compensatory postural responses, in particular across the hip and knee joints, and slow movements seemed responsible for the falls. Muscle tone was normal but reflex studies showed signs of abnormal facilitation and inhibition at various levels of the neuraxis. We conclude that the GP and SN lesions caused defective input to premotor cortical and brain stem target zones. Dysfunctioning of these zones leads to improper control of the descending ventromedial motor system responsible for locomotion, postural control, and reflex status. The deficits in upper extremity motor performance included delayed and slow movements, inaccurate amplitudes of ballistic responses, a lack of predictive control, and deficits in bimanual coordination. Sensory feedback, proprioceptive more than visual, played a powerful compensating role in rapid aiming movements. Regional blood flow (studied using 15(O)2) was reduced in multiple frontal cortical regions, among which are the hand areas of the supplementary and premotor cortex. We hypothesize that this reflected impaired functioning of these areas, caused by defective bilateral output from GP and SN, and resulting in the motor deficits of the arm and hand.

Adult↗
PubMed1994

Facial and jaw-elevator EMG activity in relation to changes in performance level during a sustained information processing task.

This study was undertaken as a further evaluation of spontaneous facial EMG activity as an index of mental effort. We investigated whether concordant alterations in task performance level and EMG amplitude existed during a sustained information processing task. The EMG of six different facial and jaw-elevator muscles was recorded in 21 subjects performing a 20 min externally paced visual two-choice serial reaction task and in 24 other subjects performing a self-paced version of this task. In both conditions, a post-hoc division was made between subjects with stable task performance parameters and subjects with a decline in performance throughout the task period. In all subject groups, there was a gradual increase in EMG activity of frontalis, corrugator, and orbicularis oris inferior muscles following task onset. As in earlier studies, this increase was interpreted as a sign of growing compensatory mental effort. In the subject groups with declining performance, however, the initial EMG increase passed into a decreasing trend towards the end of the task period whereas in the groups with stable performance, EMG increased uninterruptedly. These results were interpreted as further support for the hypothesis that EMG activity in particular facial muscles is related to the mobilization of aspecific energetic resources.

Adult↗
PubMed1984

Influence of motor unit firing statistics on the median frequency of the EMG power spectrum.

Changes in the EMG power spectrum during static fatiguing contractions are often attributed to changes in muscle fibre action potential conduction velocity. Mathematical models of the EMG power spectrum, which have been empirically confirmed, predict that under certain conditions a distinct maximum occurs in the low-frequency part of the spectrum, indicating the dominant firing rate of the motor units. The present study investigated the influence of this firing rate peak on the spectral changes during a static fatiguing contraction at 50% of maximum EMG amplitude in the frontalis and corrugator supercilii muscles. An exponential decrease of the median frequency (MF) of the EMG power spectrum was observed when the firing rate peak was absent. When the firing rate peak was present, an exaggerated decrease of MF in the beginning of the contraction was found, which was associated with an increase in firing rate peak magnitude. In later stages of the contraction, a partial recovery of MF occurred, concomitant with a decrease in firing rate peak magnitude. The influence of the firing rate peak on MF was also investigated during nonfatiguing contractions of the frontalis muscle at 20, 40, 60, and 80% of maximum EMG amplitude. A curvilinear relationship between MF and contraction strength was found, whether firing rate peaks were present or absent. The presence of firing rate peaks, however, was associated with a decrease in MF which was inversely related to contraction strength, due to the inverse relationship between firing rate peak magnitude and contraction strength.

Adolescent↗
PubMed1983

Changes in electromyogram power spectra of facial and jaw-elevator muscles during fatigue.

Endurance and changes in electromyogram (EMG) power spectra were investigated during a fatiguing static contraction at 50% of the maximum EMG amplitude in two jaw-elevator muscles (masseter and temporalis) and five facial muscles (frontalis, corrugator supercilii, zygomaticus major, orbicularis oris, and buccinator). Relatively high endurance was found in orbicularis oris, frontalis, and corrugator supercilii muscles; intermediate endurance was found in zygomaticus major, buccinator, and temporalis muscles; and low endurance was found in the masseter muscle. The last muscle showed a relatively fast linear decrease of the median frequency of the power spectrum. The other muscles showed a much slower, exponential decrease. The median frequency appeared to reflect reliably the changes in the shape of the power spectra during fatigue. Large differences between the shape of power spectra of different muscles in the unfatigued state were found. These, however, were unrelated to endurance and degree of spectral shift during fatigue.

Adolescent↗
PubMed1979

Monosynaptic spinal reflexes elicited at various phases of the EEG alpha cycle.

Relationships between the phase of EEG alpha waves and motor activities have been reported in the literature. In this study such a relation was investigated for electrically or mechanically evoked monosynaptic reflexes in the soleus muscle of normal humans. EEG alpha activity, derived from electrodes widespread over the ipsilateral and contralateral hemispheres, was tested but no relationships between alpha phase and reflex amplitudes were found.

Alpha Rhythm↗
PubMed1978

MSH/ACTH4-10 and task-induced increase in tendon reflexes and heart rate.

Earlier studies revealed that during a binary choice reaction task an increase of tendon reflex amplitudes and heart rate can be found, together with a suppression of heart rate variability. The results were interpreted as a task-induced increase in generalized arousal. In this study two experiments, consisting of a rest period and a binary choice reaction task, were done. In Experiment 1, twenty subjects, in a cross-over design, received 15 mg MSH/ACTH4-10 or a placebo. Only reflexes were recorded. In experiment 2, three groups of 9 subjects received either 30 or 15 mg MSH/ACTH4-10 or a placebo. Reflexes, heart rate and heart rate variability were recorded. Rest-task differences of reflexes and heart rate were enhanced by the drug. We hypothesized that MSH/ACTH4-10 intensified the arousal effect of the task.

Adolescent↗