Central motor reorganization was studied in 33 subjects with hemiplegic cerebral palsy. Corticospinal projections were investigated using focal magnetic stimulation of the motor cortex. Reflex pathways were examined with digital nerve stimulation. Cross-correlation analysis of multi-unit EMG was used to detect activity in branched common stem last order presynaptic inputs to motor neuron pools. The neurophysiological findings were related to the clinical outcome. In 21 of the subjects studied (64%), there was evidence for reorganization of central motor pathways. The clinical and neurophysiological findings revealed two different forms of reorganization. In both forms focal magnetic stimulation demonstrated novel ipsilateral motor pathways from the undamaged motor cortex to the hemiplegic hand. Ipsilateral projections were not demonstrated from the damaged motor cortex. Eleven subjects had intense mirror movements. In these subjects cross-correlation analysis and reflex testing suggested that corticospinal axons had branched abnormally and projected bilaterally to homologous motor neuron pools on both sides of the spinal cord. The remaining 10 subjects did not have intense mirror movements and in these subjects there was no evidence for last order branching of corticospinal axons. It was found that good function of the hemiplegic hand was associated with the presence of EMG responses in that hand following magnetic stimulation of the contralateral motor cortex. When EMG responses were absent, hand function was poor unless the subject had intense mirror movements.

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. Ann Neurol 1999;45:583–594

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.

Aim: To assess the value of postmortem bacteriology in necropsy practice, with specific emphasis on bacterial invasion of blood and cerebrospinal fluid (CSF). Methods: A review of published articles on postmortem bacteriology. Studies were selected to cover the full range of necropsy practice including adults, the perinatal period, and infancy. The review covers over 5000 necropsies, mainly in adults, but including 1108 perinatal cases and 468 cases of sudden unexpected death in infancy. Data are available on 4992 blood cultures, 1168 specimens of CSF, and 743 cultures of spleen. Results: Studies in which careful precautions have been taken to reduce contamination show that approximately two thirds of blood cultures are negative, two in nine yield a single isolate, and one in nine have a mixed growth. The postmortem interval has only a small effect on the isolation rate. A pure growth of a known pathogen has a more than 50% likelihood of being found in association with genuine infection in adults and in the perinatal period. Conclusions:The main postmortem artefact is contamination, but this can be considerably reduced by careful technique. Agonal spread is less common than is often assumed. Postmortem translocation is not a problem if the body is appropriately stored. A pure growth of a pathogen in blood or CSF should be regarded as a possible contributing factor to death at all ages.

In adults, motoneurone pools of synergistic muscles that act around a common joint share a common presynaptic drive. Common drive can be revealed by both time domain and frequency domain analysis of EMG signals. Analysis in the frequency domain reveals significant coherence in the range 1-45 Hz, with maximal coherence in low (1-12 Hz) and high (16-32 Hz) ranges. The high-frequency range depends on cortical drive to motoneurones and is coherent with cortical oscillations at approximately 20 Hz frequencies. It is of interest to know whether oscillatory drive to human motoneurone pools changes with development. In the present study we examined age-related changes in coherence between rectified surface EMG signals recorded from the short and long thumb abductor muscles during steady isometric contraction obtained while subjects abducted the thumb against a manipulandum. We analysed EMG data from 36 subjects aged between 4 and 14 years, and 11 adult subjects aged between 22 and 59 years. Using the techniques of pooled coherence analysis and the chi(2) difference of coherence test we demonstrate that between the ages of 7 and 9 years, and 12 and 14 years, there are marked increases in the prevalence and magnitude of coherence at frequencies between 11 and 45 Hz. The data from subjects aged 12-14 years were similar to those obtained from adult controls. The most significant differences between younger children and the older age groups were detected at frequencies close to 20 Hz. We believe that these are the first reported results demonstrating significant late maturational changes in the approximately 20 Hz common oscillatory drive to human motoneurone pools.