Biomedical subjects

B Brouwer

Publications and source records attributed to B Brouwer.

27 records · Page 2Linked to original sources

PubMed1992

Changes in corticospinal facilitation of lower limb spinal motor neurons after spinal cord lesions.

The projections from the cortex to the motor neurons of lower limb muscles were examined in 33 normal subjects and 16 patients with incomplete spinal cord lesions. Corticospinal neurons were excited by transcranial magnetic stimulation and the effects on single spinal motor neurons determined from peristimulus time histograms (PSTHs) of single tibialis anterior (TA) and soleus (SOL) motor units. In normal subjects magnetic stimulation produced a short latency facilitation of TA motor units but had little or no effect on SOL motor units. In the patients with spinal cord lesions magnetic stimulation also produced facilitation of TA but not SOL motor units; however, the mean latency of the TA facilitation was significantly longer (by about 14 ms) in the patient group. The F wave latencies were normal in all patients tested, suggesting that central rather than peripheral conduction was slowed. The duration of the period of increased firing probability (in TA motor units) was also significantly longer in the patients with spinal cord lesions. These changes may reflect the slowing of conduction and dispersal of conduction velocities in the corticospinal pathways as a consequence of the spinal cord lesion. No significant correlations were found between the delay of the TA facilitation and the clinical deficits in this group of patients.

Adolescent↗

PubMed1991

Altered corticospinal projections to lower limb motoneurons in subjects with cerebral palsy.

The projections of cortical neurons activated by transcranial magnetic stimulation to the motoneurons of lower limb muscles were examined in 22 normal subjects and 14 subjects with cerebral palsy (CP). In normal subjects, magnetic stimulation produced strong facilitation of tibialis anterior (TA) motoneurons, but little or no facilitation of soleus (SOL) motoneurons. This differential facilitation of TA and SOL motoneurons was observed at all stimulus sites on the scalp and all stimulus intensities at which responses could be elicited. In subjects with CP, magnetic stimulation produced almost equal facilitation of TA and SOL motoneurons. This could not be explained by differences in the excitability of the respective motoneuron pools. It is postulated that the projections from the motor cortex to spinal motoneurons are altered in CP. These abnormal projections may contribute to the impairment of voluntary movements experienced by these subjects.

Action Potentials↗

PubMed1991

Activity and post-polio fatigue.

Fatigue was studied in 12 subjects with post-polio sequelae (PPS). Results of the Fatigue Severity Scale (FSS) demonstrated a mean score of 4.8 +/- 1.6 (non-disabled scores = 2.3 +/- 0.7). The Human Activity Profile (HAP) was not sensitive enough to measure fatigue. Fifty percent of subjects scored below the first percentile based on age and sex matched norms. The Activity Record (ACTRE) results revealed that subjects spent 5% of their time resting and 1% in planning or preparation activities. Fatigue peaked in the late morning or early afternoon and was relieved by rest periods. Use of energy conservation and work simplification skills along with frequent rest periods was suggested as a possible method for managing PPS fatigue.

Activities of Daily Living↗

PubMed1990

Do injuries to the developing human brain alter corticospinal projections?

Experimental lesions of the mammalian brain involving the developing corticospinal pathways may cause these pathways to become redirected. In humans, injury to the developing brain results in disorders of movement known collectively as 'cerebral palsy'. These motor disorders differ from those produced by similar lesions in adults. We present evidence that abnormal corticospinal projections exist in subjects who have had an injury to the brain in the perinatal period. These aberrant connections, which may represent misdirected corticospinal fibers, help to explain the impairment of voluntary movements experienced by these subjects.

Cerebral Palsy↗

PubMed1990

Influence of gastro-intestinal nematodes on the productivity of dairy cattle in the wet highlands of Sri Lanka.

To study the response and economics of nematode control in cattle, trials with anthelmintics were carried out in the wet season at New Zealand farm in the highlands of Sri Lanka. Three age groups were used: stall fed yearlings, grazing heifers and lactating cows. Groups were treated with ivermectin or febantel and monitored along with control groups for faecal egg counts, growth and milk production. Treatment reduced the trichostrongylid faecal egg counts in yearlings, heifers and cows for six to 10 weeks, for more than 10 weeks and for 140 days respectively. The growth rate of treated yearlings did not increase significantly while treated heifers did grow significantly faster. Treated cows produced an average of 115 kg more milk over 133 days (P less than 0.05). The economic gains in reducing the age at first service and in terms of milk yield far outweighed the cost of anthelmintics used.

Animals↗

PubMed1990

Corticospinal projections to upper and lower limb spinal motoneurons in man.

The pattern of muscle activation produced by magnetic stimulation over the human motor cortex has been examined in normal subjects. Magnetic stimulation elicited short latency compound muscle action potentials (CMAPs) from upper limb muscles contralateral to the stimulus and from lower limb muscles bilaterally. In the upper limb, the hand and forearm muscles had the lowest thresholds for activation and the largest CMAPs. There was little or no activation of the more proximal muscles, biceps and tricepts. In the lower limb the extensor digitorum brevis and tibialis anterior had low thresholds and large CMAPs. There was little or no short latency activation of soleus. This pattern of muscle activation remained the same even when the stimulating coil was moved to various locations within a radius of 3 cm from the vertex. Recordings from individual tibialis anterior and soleus motor units indicated that the differential activation of these muscles reflected the relative amplitudes of the short latency postsynaptic potentials produced by magnetic stimulation in their motoneurons. The 'jitter' in the activation of single muscle fibers by magnetic stimulation suggests that these projections are monosynaptic. It is argued that the pattern of muscle activation reflects the projections from the cortex to motoneurons rather than the projections of afferents onto cortical neurons. We conclude that magnetic stimulation can be used to identify the projections of the corticospinal pathways in man.

Action Potentials↗

PubMed1989

Excitability of corticospinal neurons during tonic muscle contractions in man.

A magnetic stimulus applied to the human scalp over the motor cortex causes a short latency contraction of contralateral limb muscles. This is presumed to result from the indirect excitation of corticospinal neurons with monosynaptic connections to motoneurons. The excitability of these cortical neurons can be estimated from the magnitude of the postsynaptic potentials produced in spinal motoneurons by a given magnetic stimulus. In man the characteristics of these postsynaptic potentials can be derived from changes in the firing probability of single motor units. When a subject increases the level of a sustained voluntary contraction the excitability of the corticospinal neurons estimated in this way becomes less. We conclude that the additional synaptic input to motoneurons required to maintain a stronger muscle contraction comes from fiber systems other than the population of fast corticospinal neurons activated by magnetic stimulation.

Action Potentials↗

PubMed1979

Experiences of patients who undergo laryngectomy.

Fifty patients undergoing laryngectomy are described. The sociological and psychological consequences of the operation for the patient and his relatives are described, and the factors which govern the development of oesophageal speech.

Aged↗

PubMedDate not supplied

Serial casting in idiopathic toe-walkers and children with spastic cerebral palsy.

Serial casting to stretch the plantar-flexors has been advocated for idiopathic toe-walkers (ITW) and children with spastic cerebral palsy (CP), although outcomes have not been well studied. Neuromuscular function and gait were examined in eight children with CP (mean age, 7.1 years) and eight ITW (mean age, 7.5 years) casted for 3 to 6 weeks. Baseline comparisons indicated that children with CP produced lower isometric plantar-flexor torques (p<0.02) concomitant with marked co-contraction (p<0.001). greater ankle mobility (p<0.02), and higher reflex excitability (p<0.001) than ITW. After casting, both groups increased dorsiflexion range (p<0.001), decreased resistance to passive stretch (p<0.005), and produced maximal plantar-flexor torques in dorsiflexed positions (p<0.001). Reflex excitability was reduced in CP (p<0.05). Immediately postcasting, no children toe-walked, but two with CP resumed a digitigrade pattern 6 weeks later. Gait velocity and stride length did not change (p>0.05). Serial casting yielded positive outcomes that may be longer lasting in ITW.

Analysis of Variance↗