Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society
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Eloquent cortex is generally identified using a variety of techniques including direct electrical stimulation to identify motor-sensory, language, and memory cortex and somatosensory evoked potentials to identify motor-sensory cortex. It is important that these areas of cortex be identified so as to prevent damage during the course of neurosurgical procedures. Seventy epilepsy patients undergoing evaluation for epilepsy surgery with chronically implanted subdural grids were retrospectively studied using both somatosensory evoked potentials and direct electrical stimulation. ⋯ A great deal of individual variation was identified using both techniques. The results presented here support previous conclusions that the concept of homunculus somatotopy (point to point representation) of the motor-sensory cortex be abandoned and that of functional mosaicism of the motor-sensory cortex replace the earlier model. The individual variation found in the human motor-sensory cortex will require a continuation of "brain mapping" to identify eloquent cortex so that these vital areas will be spared during neocortical neurosurgical procedures.
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Fasciculation potentials (FPs) are observed in healthy individuals, but also in patients with neurogenic disorders. The exact site of origin and the clinical relevance in distinguishing, for example, amyotrophic lateral sclerosis (ALS) from other neurogenic diseases based on specific characteristics of the FPs is still a matter of debate and needs further exploration. This report describes the use of high-density surface EMG (HD-sEMG), with multiple electrodes in a compact grid to noninvasively record FPs. ⋯ It is concluded that HD-sEMG, both because of its noninvasive character and the unique spatiotemporal information, is very suitable to examine fasciculations. It allows long stable recording times and provides quantitative information. This electrophysiologic tool is expected to expand the existing knowledge of FP properties.
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J Clin Neurophysiol · Jun 2007
Success rate of motor evoked potentials for intraoperative neurophysiologic monitoring: effects of age, lesion location, and preoperative neurologic deficits.
Transcranial electrical stimulation with myogenic motor evoked potential (MEP) recording was used for intraoperative neurophysiologic monitoring in 341 consecutive "high-risk" neurosurgical or orthopedic procedures. Overall, the success rate for establishing reliable MEP response was 94.8% for upper extremities and 66.6% for lower extremities. The rate was only 39.1% for lower extremities in patients with preoperative motor deficit and up to 81% in neurologically intact adults. Further analysis demonstrated that extremes of age or the presence of a lesion in the spinal cord and motor deficit contributed to failure in obtaining reliable MEPs.