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Biomedical subjects

J L Taylor

Publications and source records attributed to J L Taylor.

At least 19 recordsLinked to original sources
PubMed2007

Muscle fatigue changes cutaneous suppression of propriospinal drive to human upper limb muscles.

Some voluntary drive reaches human upper limb muscles via cervical propriospinal premotoneurones. Stimulation of the superficial radial nerve can inhibit these premotoneurones selectively and the resultant suppression of voluntary drive to motoneurones changes on-going electromyographic (EMG) activity. We investigated whether muscle fatigue changes this cutaneous-induced suppression of propriospinal drive to motoneurones of upper limb muscles. EMG was recorded from the extensors and flexors of the wrist and elbow. In the first study (n = 10 subjects), single stimuli (2 x perception threshold; 2PT) to the superficial radial nerve were delivered during contraction of the wrist extensors, before and after sustained fatiguing contractions of wrist extensors. In the second study (n = 10), similar stimuli were applied during elbow extension, before and during fatigue of elbow extensors. In the final study (n = 10), trains of three stimuli (2PT) were delivered during contractions of wrist extensors, before and while they were fatigued. With fatigue of either the wrist or elbow extensors, EMG suppression to single cutaneous stimuli increased significantly (by approximately 75%) for the fatigued muscle (P < 0.05). Conversely, in the other muscles, which were coactivated but not principally involved in the task, inhibition decreased or facilitation increased. Trains of stimuli produced greater suppression of on-going wrist extensor EMG than single stimuli and this difference persisted with fatigue. A control study of the H reflex in extensor carpi radialis showed that the mechanism responsible for the altered EMG suppression in fatigue was not at a motoneurone level. The findings suggest that the proportion of descending drive mediated via the disynaptic propriospinal pathway or the excitability of inhibitory interneurones projecting to propriospinal neurones increases substantially to fatigued muscles, but decreases to other active muscles. This pattern of changes may maintain coordination during multimuscle movements when one group of muscles is fatigued.

Adult↗
PubMed2006

Theta burst stimulation does not reliably depress all regions of the human motor cortex.

OBJECTIVE: The excitability of the human motor cortex projecting to hand muscles can be reduced by theta burst transcranial magnetic repetitive stimulation (TBS). This study compared the magnitude and variability of changes evoked by TBS for a distal and proximal arm muscle. METHODS: Eight subjects participated in three studies. In each study, electromyographic responses (MEPs) to single-pulse transcranial magnetic stimulation assessed cortical excitability before and after 40s of TBS. In the first two studies, TBS (intensity, 80% active motor threshold) was delivered to the optimal locations for biceps or first dorsal interosseous (FDI). In the final study, weaker intensity TBS was delivered over the biceps representation. RESULTS: TBS targeting biceps produced highly variable results among subjects. For the group, MEPs were not significantly depressed. Repeat studies in individual subjects highlighted the variability of responses. For FDI, MEPs were significantly depressed 5min after TBS and remained depressed for >30min (p<0.05). No significant changes in biceps MEPs occurred with weaker TBS. CONCLUSIONS: The magnitude and reliability of TBS depends on the region of the cortex targeted. SIGNIFICANCE: Results obtained for the hand should not be considered indicative of changes that will occur in other regions of the motor cortex or the brain.

Adult↗
PubMed2006

Output of human motoneuron pools to corticospinal inputs during voluntary contractions.

This study investigated transmission of corticospinal output through motoneurons over a wide range of voluntary contraction strengths in humans. During voluntary contraction of biceps brachii, motor evoked potentials (MEPs) to transcranial magnetic stimulation of the motor cortex grow up to about 50% maximal force and then decrease. To determine whether the decrease reflects events at a cortical or spinal level, responses to stimulation of the cortex and corticospinal tract (cervicomedullary motor evoked potentials, CMEPs) as well as maximal M-waves (M(max)) were recorded during strong contractions at 50 to 100% maximum. In biceps and brachioradialis, MEPs and CMEPs (normalized to M(max)) evoked by strong stimuli decreased during strong elbow flexions. Responses were largest during contractions at 75% maximum and both potentials decreased by about 25% M(max) during maximal efforts (P < 0.001). Reductions were smaller with weaker stimuli, but again similar for MEPs and CMEPs. Thus the reduction in MEPs during strong voluntary contractions can be accounted for by reduced responsiveness of the motoneuron pool to stimulation. During strong contractions of the first dorsal interosseous, a muscle that increases voluntary force largely by frequency modulation, MEPs declined more than in either elbow flexor muscle (35% M(max), P < 0.001). This suggests that motoneuron firing rates are important determinants of evoked output from the motoneuron pool. However, motor cortical output does not appear to be limited at high contraction strengths.

Action Potentials↗
PubMed2005

Length-dependent changes in voluntary activation, maximum voluntary torque and twitch responses after eccentric damage in humans.

To assess the contribution of central and peripheral factors to changes in maximum voluntary force and its length dependence after eccentric muscle damage, voluntary and twitch torque were measured across a wide angular range, along with voluntary activation using twitch interpolation. Isometric torque from both maximum voluntary contractions (MVCs) and paired twitches to motor nerve stimulation were measured from 60 to 150 deg elbow flexion in 10 deg increments in eight subjects. Optimal angles were determined by curve fitting. Each subject then performed eccentric contractions until voluntary torque had decreased by approximately 40%. Measurements were repeated at 2 h, 1 day and 8 days post-exercise to follow acute and longer-term changes. Before exercise, the optimal angle was in the mid-range (93+/-10 deg; mean+/-s.d.) for MVCs, and at a more extended elbow angle for the twitch (106+/-6 deg, P < 0.05). Voluntary activation was generally high (> 94%) but depended on elbow angle, with activation being approximately 4% lower at the most flexed compared to the most extended angle. Two hours after exercise, MVCs decreased 40%, while twitch torque declined 70%. All subjects showed a shift in optimal angle to longer muscle lengths for MVCs (17+/-16 deg at 2 h, 14+/-7 deg at day 1, P < 0.05). This shift contributed minimally (approximately 3%) to the reduction in torque at 90 deg, as the torque-angle relation was relatively flat around the optimum. The twitch showed a smaller shift (approximately 4 deg) to longer lengths which was not statistically significant. Voluntary activation was significantly impaired in the early stages after exercise (2 h and day 1, P < 0.05), particularly at short muscle lengths. By 8 days after exercise, the optimal angle had returned to pre-exercise values, but MVC, twitch torque and voluntary activation had not fully recovered. Eccentric exercise causes a short-term shift in the optimal angle for MVCs and produces a length-dependent impairment in voluntary activation. Therefore, it appears that both central and peripheral factors limit muscle performance following eccentric damage, with limits to voluntary drive being especially important at short lengths.

Adult↗
PubMed2005

Maximal force, voluntary activation and muscle soreness after eccentric damage to human elbow flexor muscles.

Muscle damage reduces voluntary force after eccentric exercise but impaired neural drive to the muscle may also contribute. To determine whether the delayed-onset muscle soreness, which develops approximately 1 day after exercise, reduces voluntary activation and to identify the possible site for any reduction, voluntary activation of elbow flexor muscles was examined with both motor cortex and motor nerve stimulation. We measured maximal voluntary isometric torque (MVC), twitch torque, muscle soreness and voluntary activation in eight subjects before, immediately after, 2 h after, 1, 2, 4 and 8 days after eccentric exercise. Motor nerve stimulation and motor cortex stimulation were used to derive twitch torques and measures of voluntary activation. Eccentric exercise immediately reduced the MVC by 38 +/- 3% (mean +/- s.d., n = 8). The resting twitch produced by motor nerve stimulation fell by 82 +/- 6%, and the estimated resting twitch by cortical stimulation fell by 47 +/- 15%. While voluntary torque recovered after 8 days, both measures of the resting twitch remained depressed. Muscle tenderness occurred 1-2 days after exercise, and pain during contractions on days 1-4, but changes in voluntary activation did not follow this time course. Voluntary activation assessed with nerve stimulation fell 19 +/- 6% immediately after exercise but was not different from control values after 2 days. Voluntary activation assessed by motor cortex stimulation was unchanged by eccentric exercise. During MVCs, absolute increments in torque evoked by nerve and cortical stimulation behaved differently. Those to cortical stimulation decreased whereas those to nerve stimulation tended to increase. These findings suggest that reduced voluntary activation contributes to the early force loss after eccentric exercise, but that it is not due to muscle soreness. The impairment of voluntary activation to nerve stimulation but not motor cortical stimulation suggests that the activation deficit lies in the motor cortex or at a spinal level.

Adult↗
PubMed2005

The reliability and validity of general psychotic rating scales with people with mild and moderate intellectual disabilities: an empirical investigation.

BACKGROUND: Whilst assessment tools have been developed to diagnose schizophrenia in people with mild intellectual disabilities (IDs), little attention has been paid to developing reliable and valid dimensional measures of psychotic experiences with this population. This study investigates the reliability and validity of two such measures developed for the general adult psychiatric population, the Positive and Negative Syndrome Scale (PANSS) and the Psychotic Symptom Rating Scales (PSYRATS), with a population of adults with mild IDs. METHOD: Sixty-two adults with mild IDs were interviewed using the PANSS and PSYRATS, and independently interviewed using the Psychiatric Assessment Schedule--Adults with Developmental Disability (PAS-ADD) to obtain psychiatric diagnoses to the criteria of the International Classification of Diseases--Tenth Revision (ICD-10). On the basis of ICD-10 diagnosis, participants were divided into three groups: psychosis (n=11); other mental health problem (n=14); no mental health problem (n=37). PANSS and PSYRATS subscale scores were compared across these three groups and were correlated with PAS-ADD symptom scores across a number of PAS-ADD symptom domains. RESULTS: All PANSS and PSYRATS subscales showed adequate internal reliability, largely good test-retest reliability, and logical inter-correlations between subscales. The PANSS positive symptoms and the PSYRATS auditory hallucinations subscales differentiated between the psychosis group and the other groups; the PANSS general symptoms subscale differentiated between the psychosis and no mental health problem groups; and the PANSS negative symptoms and the PSYRATS delusions subscales did not differentiate between the three groups. CONCLUSIONS: The PANSS and PSYRATS are promising measures for use with people with mild IDs and psychotic experiences, although further investigation of items relating to negative symptoms and delusions is warranted.

Adolescent↗
PubMed2004

Life events and psychiatric symptoms in adults with intellectual disabilities.

BACKGROUND: Previous research has indicated that children and adults with intellectual disabilities (ID) may respond to traumatic and other life events in a similar way to the general population. However, few studies have charted the extent of exposure to recent life events in samples of adults with ID and the association of such exposure with general psychiatric problems. METHODS: Adults with ID (n = 1155) in community and residential services in a county district in North-east England were assessed using the Psychiatric Assessment for Adults with Developmental Disabilities Checklist (PAS-ADD Checklist), which includes a checklist of recent life events. Data were provided by informants who knew the index client well. RESULTS: Within the 12 months before data collection, the five most frequently experienced life events were: moving residence (15.5% of sample), serious illness of close relative or friend (9.0%), serious problem with close friend, neighbour or relative (8.8%), serious illness or injury to self (8.5%), and death of close family friend or other relative (8.3%). Overall, 46.3% had experienced one or more significant life events in the previous 12 months and 17.4% had experienced two or more. Logistic regression analysis revealed that the presence of one or more life events in the previous 12 months added significantly to the classification of psychiatric caseness predicted by demographic variables (age, sex, residence in community or hospital) on the PAS-ADD Affective Disorder scale. Overall, the odds ratio for affective disorder given exposure to one or more life events was 2.23 [95% confidence interval (CI) = 1.56, 3.18]. CONCLUSIONS: Small, but potentially significant relationships were found between life events exposure and psychiatric problems in adults with ID. Further research is needed to explore the causal direction of this relationship and also to develop more sensitive measures of life events relevant to the situation of adults in residential and community service environments.

Adolescent↗
PubMed2004

Screening for psychiatric symptoms: PAS-ADD Checklist norms for adults with intellectual disabilities.

BACKGROUND: The Psychiatric Assessment Schedule for Adults with Developmental Disabilities Checklist (PAS-ADD Checklist) is a screening instrument designed to help carers recognize likely mental health problems in people with intellectual disabilities (ID). To date there are no published PAS-ADD Checklist data on a large nonpsychiatric population of adults with ID, an important step towards developing norms for comparative purposes. METHODS: Informants who had known participants for a median 24 months completed the PAS-ADD Checklist on 1155 adults with ID living in community, residential care and hospital settings in a county district in the North-east of England. RESULTS: Normative data were obtained for the PAS-ADD Checklist for the study population with reference to gender, age, and type of residence. The overall prevalence of mental health problems was 20.1%, and the rates for affective/neurotic, organic and psychotic disorders were 14%, 3.9%, and 10.2%, respectively. Significant differences in the rates for particular disorders were found across gender, age and, residence type. CONCLUSIONS: The rates of mental disorders found in the study population were consistent with previous studies of general populations of people with ID using over-inclusive screening instruments. The PAS-ADD Checklist appears to be an easy-to-use and sensitive tool for identifying mental health cases in ID populations, but further investigation is required concerning the specificity of the instrument.

Adolescent↗
PubMed2004

Noninvasive stimulation of the human corticospinal tract.

Spinal tracts can be stimulated noninvasively in human subjects by passing a high-voltage stimulus between the mastoids or by magnetic stimulation over the back of the head. The stimulus probably activates the corticospinal tract at the cervicomedullary junction (pyramidal decussation) and evokes large, short-latency motor responses in the arm muscles. These responses have a large monosynaptic component. Responses in leg muscles can be elicited by cervicomedullary junction stimulation or by stimulation over the cervical or thoracic spine. Because nerve roots are more easily activated than spinal tracts, stimulus spread to motor axons can occur. Facilitation of responses by voluntary activity confirms that the responses are evoked synaptically. Stimulation of the corticospinal tract is useful in studies of central conduction and studies of the behavior of motoneurons during different tasks. It also provides an important comparison to allow interpretation of changes in responses to stimulation of the motor cortex. The major drawback to the use of electrical stimulation of the corticospinal tract is that each stimulus is transiently painful.

Electric Stimulation↗
PubMed2003

Working with sex offenders with intellectual disability: evaluation of an introductory workshop for direct care staff.

BACKGROUND: Sexual aggression by men with intellectual disability (ID) is a serious problem requiring attention from the relevant agencies. Training for staff working with this problem is often not given sufficient attention and is rarely evaluated. In the present study, an introductory workshop for direct care staff that aimed to increase knowledge and improve attitudes towards work with this client group was evaluated. METHOD: Sixty-six staff working in inpatient and community settings completed a 2.5-day workshop. Before training began, the participants completed a survey questionnaire concerning their experiences of work with this client group. An assessment of their knowledge and attitudes was carried out prior to and at the end of training in order to evaluate any changes. The participants also rated the effectiveness of the workshop and their level of satisfaction with the training at the end of the workshop. RESULTS: The participants' knowledge and attitudes improved significantly following the workshop. Staff with greater experience over time and those who had worked with fewer sex offender clients responded to different aspects of the training. The participants' ratings indicated that they were highly satisfied with the training and found it to be effective. CONCLUSIONS: Brief workshop training is acceptable to and can be effective in improving the knowledge, attitudes and confidence of direct care staff working with sex offenders with ID. However, because the results are based on participant self-report, caution should be exercised concerning their external validity.

Attitude of Health Personnel↗
PubMed2002

Donepezil and flight simulator performance: effects on retention of complex skills.

We report a randomized, double-blind, parallel group, placebo-controlled study to test the effects of the acetylcholinesterase inhibitor, donepezil (5 mg/d for 30 days), on aircraft pilot performance in 18 licensed pilots with mean age of 52 years. After 30 days of treatment, the donepezil group showed greater ability to retain the capacity to perform a set of complex simulator tasks than the placebo group, p < 0.05. Donepezil appears to have beneficial effects on retention of training on complex aviation tasks in nondemented older adults.

Adult↗
PubMed2002

Cortically evoked neural volleys to the human hand are increased during ischaemic block of the forearm.

Reorganisation of the motor cortex may occur after limb amputation or spinal cord injury. In humans, transcranial magnetic stimulation (TMS) shows expansion of motor cortical representations of muscles proximal to the injury. Similarly, ischaemic block of the hand can increase acutely the representation of the biceps muscle, measured by increased biceps motor potentials evoked by TMS. It is thought that this increase occurs at the expense of the cortical representation of the paralysed and deafferented hand muscles but this has never been investigated. To study what changes occur in the cortical representation of the hand muscles during ischaemic block, a tungsten microelectrode was inserted into the ulnar or median nerve above the elbow and the size of the neural potential elicited by TMS in fascicles supplying the hand was measured in seven subjects. Prior to ischaemia, TMS evoked EMG responses in the intrinsic hand muscles. In the nerve, a brief motor potential preceded the response in the muscle and was followed by a contraction-induced sensory potential. During 40 min of ischaemia produced by a blood pressure cuff inflated around the forearm to 210 mmHg, the EMG response to TMS and the sensory potential from the hand were progressively blocked. However, the motor neural evoked potential showed a significant increase in amplitude during the ischaemic period (30.5 %, P = 0.005). The increase in the neural potential suggests that output to the hand evoked from the cortex by TMS was not decreased by ischaemic block. Thus, we conclude that the increased response of biceps to TMS during distal ischaemia is not accompanied by a corresponding decrease in the motor cortical representation of the hand.

Adult↗
PubMed2002

A review of the assessment and treatment of anger and aggression in offenders with intellectual disability.

Rates of aggression amongst people with intellectual disability (ID) have been found to be high in studies conducted on several continents across a number of service settings. Aggression is the primary reason for people with ID to be admitted or re-admitted to institutional settings, and it is also the main reason for individuals in this client group to be prescribed behaviour-control drugs. Anger is a significant activator of aggression, but little is known about the emotional aspects of the lives of people with ID. There are many reasons for this, but a lack of reliable and validated assessment measures is chief among them. The present review found that very little work has been conducted to date concerning the development of robust tools for assessing anger and aggression in this population. A narrative review of interventions for reducing aggression and anger in people with ID showed that there is virtually no evidence to support the use of psychotropic medications. Research has shown that behavioural interventions can be effective; however, they are intrusive and have not been tested in naturalistic settings with higher-functioning clients and low-frequency aggression. More recently, cognitive-behavioural interventions have shown promise, but the mechanisms for effective change have yet to be delineated. Priority research questions relating to assessment, treatment and therapeutic skills in working with anger and aggression problems are offered by the present review.

Aggression↗
PubMed2001

Mechanisms of motor-evoked potential facilitation following prolonged dual peripheral and central stimulation in humans.

1. Repetitive electrical peripheral nerve or muscle stimulation can induce a lasting increase in the excitability of the corticomotor projection. By pairing peripheral stimulation with transcranial magnetic brain stimulation it is possible to shorten the duration of stimulation needed to induce this effect. This ability to induce excitability changes in the motor cortex may be of significance for the rehabilitation of brain-injured patients. The mechanisms responsible for the increases in excitability have not been investigated thoroughly. 2. Using two paired transcranial magnetic stimuli protocols we investigated the excitability of intracortical inhibitory and excitatory systems before and following a period of repetitive dual muscle and brain stimulation. The dual stimulation consisted of motor point stimulation of first dorsal interosseous (FDI; 10 Hz trains of 1 ms square waves for 500 ms) delivered at one train every 10 s, paired with single transcranial magnetic stimulation given 25 ms after the onset of the train. 3. Following 30 min of dual stimulation, motor-evoked potentials (MEPs) were significantly increased in amplitude. During this period of MEP facilitation there was no significant difference in the level of intracortical inhibition. There was, however, a significant increase in the intracortical facilitation demonstrated with paired magnetic stimuli. The increase in facilitation was seen only at short interstimulus intervals (0.8-2.0 ms). These intervals comprised a peak in the time course of facilitation, which is thought to reflect I wave interaction within the motor cortex. 4. The relevance of this finding to the MEP facilitation seen following dual peripheral and central stimulation is discussed.

Adult↗
PubMed2001

Unexpected reflex response to transmastoid stimulation in human subjects during near-maximal effort.

1. In human subjects, a high-voltage electrical pulse between electrodes fixed over the mastoid processes activates descending tract axons at the level of the cervico-medullary junction to produce motor responses (cevicomedullary evoked responses; CMEPs) in the biceps brachii and brachioradialis muscles. 2. During isometric maximal voluntary contractions (MVCs) of the elbow flexors, CMEPs in the biceps brachii and brachioradialis muscles are sometimes followed by a second compound muscle action potential. This response can be observed in single trials (amplitude of up to 60 % of the maximal M wave) and follows the CMEP by about 16 ms in both muscles. The response only occurs during very strong voluntary contractions. 3. The second response following transmastoid stimulation appears with stimulation intensities that are at the threshold for evoking a CMEP in the contracting muscles. The response grows with increasing stimulus intensity, but then decreases in amplitude and finally disappears at high stimulation intensities. 4. A single stimulus to the brachial plexus during MVCs can also elicit a second response (following the M wave) in the biceps brachii and brachioradialis muscles. The latency of this response is 3-4 ms longer than that of the second response observed following transmastoid stimulation. This difference in latency is consistent with a reflex response to stimulation of large-diameter afferents. 5. The amplitude of the second response to transmastoid stimulation can be reduced by appropriately timed subthreshold transcranial magnetic stimuli. This result is consistent with intracortical inhibition of the response. 6. We suggest that transmastoid stimulation can elicit a large transcortical reflex response in the biceps brachii and brachioradialis muscles. The response travels via the motor cortex but is only apparent during near-maximal voluntary efforts.

Action Potentials↗
PubMed2001

Changes in respiratory sensations induced by lobeline after human bilateral lung transplantation.

1. The sensations evoked by the injection of lobeline into the right antecubital vein were studied in 8 subjects after bilateral lung transplantation and 10 control subjects. In control subjects, two distinct sensations were experienced. There was an early noxious sensation (onset approximately 10 s) followed by a late sensation of breathlessness (onset approximately 26 s) associated with involuntary hyperventilation. The early sensation was accompanied by respiratory and cardiovascular changes. 2. In contrast to control subjects, the early respiratory events and the noxious sensations evoked by injections of lobeline (18-60 microg kg(-1)) did not occur in subjects with recent bilateral lung transplantation. This suggests that the early respiratory sensations are mediated by the discharge of receptors in the lungs. 3. The late hyperventilation and the accompanying sensation of breathlessness occurred in both transplant and control subjects and are therefore likely to be mediated by receptors elsewhere in the body, presumably systemic arterial chemoreceptors stimulated by lobeline. 4. In control subjects, but not transplant subjects, there was a consistent decrease in mean arterial pressure associated with the lobeline injection. This suggests that pulmonary afferents mediate the hypotension. 5. For transplant subjects studied more than a year after transplantation, there was some evidence that the noxious respiratory sensations evoked by lobeline had returned. This suggests that some functional reinnervation of pulmonary afferents may occur.

Adult↗