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Biomedical subjects

J A Stephens

Publications and source records attributed to J A Stephens.

At least 19 recordsLinked to original sources
PubMed2003

Abnormal cortex-muscle interactions in subjects with X-linked Kallmann's syndrome and mirror movements.

X-linked Kallmann's (XKS) subjects, who display mirror movements, have abnormal corticospinal tracts which innervate motoneurons of the left and right distal muscles of the upper limb. The size of the abnormal ipsilateral projection is variable. We have used coherence and cumulant analysis between EEG and first dorsal interosseous muscle (1DI) EMG to explore mechanisms underlying mirror movements in three XKS subjects. Results are compared with those of three normal subjects. We argue that significant coherence is functionally relevant when associated with a negative cumulant at an appropriate lag. Given this, normal subjects showed coherence at approximately 22 Hz between the EEG recorded over the sensori-motor cortex contralateral to the voluntarily moved hand and the 1DI EMG of this hand. No significant coherence was seen between 1DI EMG and the sensori-motor cortex ipsilateral to the muscle activity. In contrast, two of the XKS subjects (K2 and K4) had significant coherence at 22 Hz, together with a negative cumulant at an appropriate lag, between the ipsilateral cortical EEG and the 1DI EMG of the voluntarily activated hand. This implies that activity in the abnormal ipsilateral corticospinal projection can contribute to the voluntary drive. For these two subjects, the ipsilateral corticospinal projection was greater than the contralateral projection, as revealed using magnetic brain stimulation. In one of these subjects, K4, significant 22 Hz coherence and negative cumulant was also seen between the EMG of the voluntarily activated hand and the cortex contralateral to this hand. In the third subject, K4a, coherence and negative cumulant was detected between the EMG of the voluntary side and the cortical activity contralateral to this hand. The contralateral cortico spinal projection of this subject was greater than the ipsilateral projection. Regarding the mirroring hand of the XKS subjects, coherence (with negative cumulant at an appropriate lag) was seen in all three subjects between the EMG recorded from the mirroring hand and cortical EEG ipsilateral to this hand. This provides evidence that activity in the aberrant ipsilateral projection is involved in producing the drive that results in mirror movements. In one subject, K4, coherence and negative cumulant was also seen between the EMG of the mirroring hand and motor cortical activity contralateral to this hand. Thus, in this subject, activity in the corticospinal projection contralateral to the mirroring hand also contributed to the mirror movements. In conclusion, this study has provided further evidence that the 22 Hz coherence seen between EEG and EMG is dependent upon corticospinal activity and has furthered our understanding of mechanisms underlying mirror movements.

Adult↗
PubMed2003

Organization of the central control of muscles of facial expression in man.

Surface EMGs were recorded simultaneously from ipsilateral pairs of facial muscles while subjects made three different common facial expressions: the smile, a sad expression and an expression of horror, and three contrived facial expressions. Central peaks were found in the cross-correlograms of EMG activity recorded from the orbicularis oculi and zygomaticus major during smiling, the corrugator and depressor anguli oris during the sad look and the frontalis and mentalis during the horror look. The size of the central peak was significantly greater between the orbicularis oculi and zygomaticus major during smiling. It is concluded that co-contraction of facial muscles during some facial expressions are accompanied by the presence of common synaptic drive to the motoneurones supplying the muscles involved. Central peaks were found in the cross-correlograms of EMG activity recorded from the frontalis and depressor anguli oris during a contrived expression. However, no central peaks were found in the cross-correlograms of EMG activity recorded from the frontalis and orbicularis oculi or from the frontalis and zygomaticus major during the other two contrived expressions. It is concluded that a common synaptic drive is not present between all possible facial muscle pairs and suggests a functional role for the synergy. The origin of the common drive is discussed. It is concluded that activity in branches of common stem last-order presynaptic input fibres to motoneurones innervating the different facial muscles and presynaptic synchronization of input activity to the different motoneurone pools is involved. The former probably contributes more to the drive to the orbicularis oculi and zygomaticus major during smiling, while the latter is probably more prevalent in the corrugator and depressor anguli oris during the sad look, the frontalis and mentalis during the horror look and the frontalis and depressor anguli oris during one of the contrived expressions. The strength of common synaptic drive is inversely related to the degree of separate control that can be exhibited by the facial muscles involved.

Electrodes↗
PubMed2002

Finger movement is associated with attenuated cutaneous reflexes recorded from human first dorsal interosseous muscle.

Cutaneomuscular reflexes (CMR) have been recorded from the first dorsal interosseous muscle (1DI) of the preferred hand, somatosensory evoked potentials (SEP) were recorded from the contralateral sensory cortex and the sensory nerve action potential (SNAP) was recorded from the median nerve of 15 adult subjects whilst electrically stimulating the digital nerves of the index finger. Subjects performed the following tasks (a) a sustained abduction of the index finger against resistance at 10-20 % maximum voluntary contraction (MVC), and (b) abduction of the index finger as in (a) whilst performing self paced low amplitude tapping of the (i) index finger, (ii) thumb, (iii) middle finger, (iv) little finger and (v) ipsilateral foot. The E2 component of the CMR and the N20/P25 components of the SEP were significantly reduced during finger tapping (P < 0.05). This reduction was independent of which finger was tapping (P > 0.05). There was a significant (qualitative) relationship between the decrease in the size of the E2 component of the CMR and the N20/P25 components of the SEP ((2) test; P < 0.05). There were no significant changes in E1 and I1 (P > 0.05). The size of the SNAP was independent of task (P > 0.05). The size of the E1, I1, E2 components of the CMR, and the N20/P25 components of the SEP were unaltered during foot tapping (P > 0.05, n = 4). We conclude that the decrease in size of the E2 component associated with finger tapping results from gating of the digital nerve input.

Adolescent↗
PubMed2001

Physiological tremor in human subjects with X-linked Kallmann's syndrome and mirror movements.

Human physiological tremor consists of mechanical-reflex and neurogenic components. The origin of the neurogenic component, classically detected in the frequency range 7-12 Hz, has been much debated. We have studied six subjects with X-linked Kallmann's syndrome (XKS) and mirror movements. In these subjects unilateral magnetic brain stimulation results in abnormal bilateral EMG responses. Furthermore, abnormal sharing of central nervous inputs between the left and right motoneurone pools results in both abnormal motor unit synchronisation between left and right EMGs and abnormal sharing of long but not short-latency cutaneomuscular reflexes. XKS subjects with mirror movements thus provide a model for studying the central origin of physiological tremor. During sustained co-extension of the left and right index fingers, simultaneous finger tremor and extensor indicis (EI) EMGs were recorded and cross-correlated. The tremor and EMG signals were also subjected to time and frequency domain analysis.Results of frequency domain analysis between ipsilateral finger tremor and EI EMG were similar for both control and XKS subjects. However, in contrast to the controls, short-term synchronisation of left and right EI motor unit activity and significant coherence between left and right EMG, left and right tremor, left EMG and right tremor and right EMG and left tremor were found in XKS subjects. The frequency range (6-40 Hz) and coherence values between left and right were similar to ipsilateral coherence values of rectified EMG and tremor. These data provide strong evidence to support the hypothesis that the neurogenic component of physiological tremor is supraspinal in origin and ranges from 6 to 40 Hz.

Adult↗
PubMed2001

Microsurgery in private practice: is it feasible economically?

Microsurgical free tissue transfer and replantations have long been the bailiwick of academic training centers and tertiary referral centers. However, the authors' experience with more than 350 consecutive free tissue transfers during a span of 15 years in a purely private setting illustrates the changing economics of the medical environment in that time frame. These data provide insight into the feasibility and practicality of maintaining a microsurgical practice outside an academic medical center.

Adolescent↗
PubMed2001

Effects of a nutritional supplement on periodontal status.

Among the recommendations for the maintenance of gingival and periodontal health, few have focused on the value of nutritional supplements. The purpose of this study was to compare the effect of certain nutritional and plant-derived nutraceuticals and a placebo tablet in the reduction of gingivitis, bleeding, probing depths, and attachment levels in a 60-day two-cell, randomized, parallel clinical trial for patients with Type II periodontal disease. The vitamin therapy was introduced as an adjunct to patient homecare to determine if there was a quantifiable improvement to soft-tissue health and periodontal damage. Sixty-three patients were randomly divided into two groups of 32 and 31 subjects and given either a vitamin tablet containing seven active ingredients (experimental treatment) or a placebo tablet. The clinical parameters assessed were the gingival index (GI), bleeding index (BI), periodontal pocket depth (PD), and attachment levels (AL), and were recorded at baseline and 60 days. Patients took the assigned tablet at breakfast and at dinner after brushing their teeth twice daily. After 60 days, the data showed a clinical reduction in the GI, BI, and PD for the experimental group (P < .0001). There were no significant changes for AL with either the experimental or the placebo group. When the data were further analyzed for pocket depths of > or = 4 mm in patients receiving the experimental treatment, there were clinically significant improvements in the GI and PD from baseline to 60 days (P < .0001), but no significant differences in the BI and AL. There were no statistical differences in any of the indices when the data were compared between men and women. The results of the present study suggest that a multi-vitamin nutritional supplement might be a beneficial adjunct to the required established periodontal treatment.

Adult↗
PubMed2000

Habituation of cutaneomuscular reflexes recorded from the first dorsal interosseous and triceps muscle in man.

Cutaneomuscular reflexes have been recorded from the first dorsal interosseous muscle during a sustained abduction of the index finger of 20 subjects (25 recordings) following stimulation of the digital nerves at the following frequencies: 2 Hz, 3 Hz, 5 Hz, 7 Hz and 9 Hz, presented in random order. Five hundred stimuli were given at each frequency. EMG was rectified and consecutive batches of 100 sweeps of each set of 500 responses were averaged time locked to the stimulus. All reflex components, E1, I1 and E2, exhibit habituation with the E1 component habituating the most and the I1 component the least. There was considerable variation in the rate of habituation between subjects. The rate of habituation was independent of the frequency of stimulation. Reflex responses were recorded from the triceps brachii muscle in eight subjects; this reflex response habituated at a faster rate than the E2 component recorded from the first dorsal interosseous muscle. These results are discussed in relation to the choice of stimulus parameters for the clinical testing of cutaneous reflexes. We conclude that it is important to consistently average the same number of responses.

Adolescent↗
PubMed2000

Acquisition of a new motor skill is accompanied by changes incutaneomuscular reflex responses recorded from finger muscles in man.

Cutaneomuscular reflex (CMR) responses and motor unit synchronisation have been recorded to investigate possible reorganisation of central nervous pathways in six healthy adults learning a novel skill with the non-dominant hand. Multi-unit surface EMG signals were recorded from first dorsal interosseous (1DI) and abductor digiti minimi (ADM) muscles during sustained flexion of the index finger and abduction of the little finger (flex/ab) and during bilateral controlled finger abduction (ab/ab). CMR responses were elicited by concomitant stimulation of the digital nerves of the index finger at 2.5 times threshold for perception. For training purposes the subject practised the novel flex/ab task phasically at a rate of 1 Hz for 10 min daily for 12 days. Cortically mediated components of the CMR responses recorded from 1DI and ADM were significantly larger in both muscles during training. Taking the data for all subjects together, when subjects performed sustained flex/ab (novel task), the size of the I1 and E2 components were increased by 25 and 55% in IDI and 192 and 167% in ADM (Mann-Whitney U-test, P<0.05). Corresponding values for sustained ab/ab were more modest: 31 and 16% in 1DI and 88 and 54% in ADM. Changes in the size of the spinal E1 component were not the same in each muscle: values for sustained flex/ab and ab/ab were 33 and 31% smaller in 1DI and 89 and 59% larger in ADM. No significant changes were found in the amount of synchrony of motor unit firing between 1DI and ADM when subjects performed either task during training. These results suggest that learning a new motor skill produces changes which take place predominantly in the cortical pathways of the CMR and these may be due to changed connectivity within motor and/or sensory cortex which has previously been shown in the monkey.

Adult↗
PubMed2000

Risk factors associated with anabolic-androgenic steroid use among adolescents.

To identify risk factors associated with anabolic-androgenic steroid (AAS) use among adolescents, computerised and manual literature searches were performed and the resultant local, state, national and international reports of illicit AAS use by adolescents that referenced risk factors were reviewed. Results indicate that adolescent AAS users are significantly more likely to be males and to use other illicit drugs, alcohol and tobacco. Student athletes are also more likely than non-athletes to use AAS, and football players, wrestlers, weightlifters and bodybuilders have significantly higher prevalence rates than students not engaged in these activities. Currently, only a partial profile can be created to characterise the adolescent AAS user. Further research will be needed before associations can be made with a reasonable degree of confidence regarding risk factors such as athletic participation, ethnicity, socioeconomic status and educational level. More importantly, to improve prevention and intervention strategies, a better understanding of the process involved in initiating AAS use is needed, including vulnerability factors, age of initiation and the use of other illicit drugs.

Adolescent↗
PubMed1999

A neurophysiological study of mirror movements in adults and children.

The mechanism underlying mirrored activity/movements in normal individuals is unknown. To investigate this, we studied 11 adults and 39 children who performed sequential finger-thumb opposition or repetitive index finger abduction. Surface electromyographic (EMG) activity recorded from the left and right first dorsal interosseous muscles (1DI) during unilateral sequential finger-thumb opposition (voluntarily activated muscle, 1DIvol) showed mirrored EMG activity (homologous muscle of the opposite hand, 1DImm) that decreased with increasing age. The time of onset of involuntary compared with voluntary EMG activity was variable but could start at the same time. A significant increase in E2 (transcortical component) size of the cutaneomuscular reflex recorded from the 1DImm indicated increased excitability of the motor cortex ipsilateral to the 1DIvol during active index finger abduction compared with the 1DIvol relaxed. Transcranial magnetic stimulation, using the Bistim technique, indicated that the transcallosal inhibitory pathway in children may not operate in the same way as in the adult. Cross-correlation analysis did not detect shared synaptic input to motoneuron pools innervating homologous left and right hand muscles. We conclude that the mirrored movements/activity observed in healthy adults and children are produced by simultaneous activation of crossed corticospinal pathways originating from both left and right motor cortices.

Adolescent↗
PubMed1999

Cutaneomuscular reflex responses recorded from the lower limb in children and adolescents with cerebral palsy.

Cutaneomuscular reflex (CMR) responses were recorded from lower-limb and trunk muscles in 27 subjects with cerebral palsy (CP) (spastic, 21; athetoid, six) and in neurologically healthy (control) subjects, aged 3 to 15 years, while standing. In the 21 subjects with spastic CP, but not in the six subjects with athetoid CP, CMR responses were more widely distributed between ipsilateral lower-limb and trunk muscles compared with age-matched control children. CMR responses in older subjects with CP were similar to younger control subjects, lacking supraspinally mediated, long-latency components. Short-latency, spinally-mediated, excitatory CMR components were seen simultaneously in pairs of distal, antagonistic lower-limb muscles in half of the subjects with spastic CP, but in none of the control children. In subjects with spastic-type CP, the abnormal reflex responses indicate disordered spinal and supraspinal inputs to motor neurones, although there was no convincing correlation between these responses and the severity of spasticity.

Adolescent↗
PubMed1999

Does abnormal branching of inputs to motor neurones explain abnormal muscle cocontraction in cerebral palsy?

The common synaptic drive shared between two groups of motor neurones synchronizes the timing of discharges between the motor-neurone groups. Recordings were made of motor-unit discharges during cocontraction of ipsilateral pairs of thumb muscles in eight subjects with cerebral palsy (CP) aged 4 to 13 years and eight neurologically healthy subjects aged 4 to 12 years, and in pairs of lower-limb muscles in 21 subjects with CP and 21 control subjects, both aged 3 to 15 years. Common synaptic drive, likely to be derived at least partly from activity in branched corticospinal-tract neurones, produced motor-unit synchronization between pairs of thumb muscles in control subjects but was absent in all subjects with CP. Motor unit synchronization was not found between lower-limb antagonist muscles that cocontract abnormally in CP, nor was synchronization present in more widely separated muscle pairs. Therefore, abnormal patterns of muscle activation and more widespread muscle reflex responses do not result from an abnormal distribution of common synaptic drive in CP.

Adolescent↗
PubMed1998

Efficacy of an alcohol-free chlorhexidine mouthrinse as an antimicrobial agent.

STATEMENT OF PROBLEM: Antimicrobial mouthrinses have become an important part of comprehensive dental care. However, mouthrinses that contain alcohol have been shown to be detrimental to patients undergoing radiation therapy for head and neck cancer, to some immunocompromised patients, to families with small children, and to persons sensitive to alcohol. PURPOSE: This study evaluated the effectiveness of alcohol-free, 0.12% chlorhexidine mouthrinse in reducing microbial levels when compared with commercially available 0.12% chlorhexidine (CHX) and essential oils mouthrinses. MATERIAL AND METHODS: This study consisted of both in vitro and in vivo investigations. The double-blind study included 32 subjects randomly assigned to 3 groups, equalized according to the indices tested. One group (n = 11) received essential oils rinse; the second group (n = 11) received CHX; and the last group (n = 10) received the alcohol-free CHX. Subjects were asked not to use any mechanical means of oral hygiene for 21 days. The in vitro part of the study consisted of Streptococcus mutans strip tests. RESULTS: Mean plaque scores for both CHX products decreased after 21 days, whereas the mean for the essential oils increased. Bleeding and gingival index scores for all 3 groups increased, which may be due to the initially healthy tissues of the participants. Relative microbial growth for S mutans for both the CHX products decreased to 0 after 21 days, whereas the counts for the essential oils group remained varied.

Adult↗
PubMed1998

Abnormal motor unit synchronization of antagonist muscles underlies pathological co-contraction in upper limb dystonia.

The aim of this study was to examine the pathophysiological mechanisms underlying co-contraction in patients with dystonia (n = 6) and writer's cramp (n = 5). Multi-unit needle and surface EMGs were recorded from extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles during motor tasks that elicited dystonia or writer's cramp. The EMGs from ECR and FCR were recorded simultaneously and analysed using cross-correlation analysis. Similar recordings were obtained from healthy age- and sex-matched control subjects (n = 8). Despite co-contraction of the muscles, cross-correlograms from the healthy subjects did not reveal evidence of motor unit synchronization. Cross-correlograms from the dystonic subjects revealed a central peak with a median duration of 37 ms, indicating broad-peak motor unit synchronization. Cross-correlograms from patients with writer's cramp were either flat or modulated by a 11-12-Hz tremor. Frequency-domain analysis of ECR and FCR EMGs demonstrated significant coherence in the patients with dystonia and writer's cramp. These results indicate that co-contraction in dystonia is neurophysiologically distinct from voluntary co-contraction and is produced by abnormal synchronization of presynaptic inputs to antagonist motor neuron pools. ECR and FCR co-contraction in writer's cramp may be a compensatory process under voluntary control.

Adolescent↗
PubMed1997

A review of recent applications of cross-correlation methodologies to human motor unit recording.

This article reviews some recent applications of time and frequency domain cross-correlation techniques to human motor unit recording. These techniques may be used to examine the pre-synaptic mechanisms involved in control of motoneuron activity during on-going motor tasks in man without the need for imposed and artificial perturbations of the system. In this review we examine, through several examples, areas in which insights have been gained into the basic neurophysiological processes that bring about motoneuron firing in man and illustrate how these processes are affected by central nervous system pathology. We will demonstrate that synchronization and coherence may be revealed between human motor unit discharges and give examples that support the hypothesis that these phenomena are generated by activity in a focused common corticospinal input to spinal motoneurons. Disruption of central motor pathways due to diseases of the nervous system leads to pathophysiological alterations in the activity of these pre-synaptic motoneuron inputs that can be revealed by cross-correlation analysis of motor unit discharges. The significance of these studies and outstanding questions in this field are discussed.

Electromyography↗
PubMed1997

Cross-correlation analysis of motor unit activity recorded from two separate thumb muscles during development in man.

1. Multi-unit surface EMG signals were recorded from the short and long thumb abductor muscles of seventy-five children aged from 4 to 15 years and from nine adults during simultaneous abduction and extension of the left and right thumb. Ability to perform independent finger movements was investigated by timing a series of sequential finger-to-thumb oppositions. 2. Cross-correlograms were constructed from the discharges of motor units recorded from the long and short abductor muscles acting on the same thumb. In the majority of subjects, short duration central peaks were present indicating the presence of a common drive to the motoneurone pools innervating these two muscles. Except for those subjects aged 4 and 5 years, the size of these central correlogram peaks did not differ significantly between the dominant and non-dominant hands. 3. The prevalence of central cross-correlogram peaks in different subjects increased from the age of 4 years to 15 years. The size of the central cross-correlogram peak increased with age up to 10 years but did not alter significantly after this age. The duration of the central peak steadily decreased over the age range of 4 to 15 years. 4. Multilinear regression analysis of data recorded from children revealed that there was a positive, but weak, correlation between the size of the cross-correlogram peak and the rate of performance of sequential finger movements after having controlled for age.

Adult↗
PubMed1997

Mirror movements in X-linked Kallmann's syndrome. I. A neurophysiological study.

Possible mechanisms underlying the pathological mirror movements that are seen in the majority of patients with X-linked Kallmann's syndrome have been investigated using neurophysiological techniques. An EMG was recorded from the first dorsal interosseous muscle (1DI) during voluntary self-paced abduction of one indexed finger; EMG activity could also be recorded simultaneously from the contralateral 1DI. There was no significant difference between the time of onset of the bursts of voluntary and involuntary mirroring EMG. Focal magnetic stimulation of the hand area of the motor cortex revealed the presence of fast conducting bilateral corticospinal projections from each motor cortex in all subjects. However, both inter- and intra-subject differences exist when considering the ratio of ipsilaterally to contralaterally projecting axons. Cross-correlation analysis of multi-unit EMGs recorded during simultaneous voluntary sustained activation of homologous left and right pairs of distal upper limb muscles was performed. A short duration central peak was seen in the cross-correlograms indicating the presence of a common drive to left and right homologous motor neuron pools. This common drive may result from the synchronous activation of intermingled ipsilaterally and contralaterally projecting corticospinal neurons in the motor cortex. Cutaneomuscular reflexes were recorded from the 1DI following stimulation of the digital nerves of the index finger. Typically each reflex comprises spinal and longer latency trans-cortical components. In these subjects, the long latency components of the reflex response could, in addition, be recorded from the 1DI of the non-stimulated side. We conclude that these subject have a novel ipsilateral at least in part, for the pathological mirroring.

Adolescent↗