1. EMG responses evoked in hand muscles by transcranial stimulation over the motor cortex were conditioned by a single motor threshold electrical stimulus to the median nerve at the wrist in a total of ten healthy subjects and in five patients who had electrodes implanted chronically into the cervical epidural space. 2. The median nerve stimulus suppressed responses evoked by transcranial magnetic stimulation (TMS) in relaxed or active muscle. The minimum interval between the stimuli at which this occurred was 19 ms. A similar effect was seen if electrical stimulation was applied to the digital nerves of the first two fingers. 3. Median or digital nerve stimulation could suppress the responses evoked in active muscle by transcranial electrical stimulation over the motor cortex, but the effect was much less than with magnetic stimulation. 4. During contraction without TMS, both types of conditioning stimuli evoked a cutaneomuscular reflex that began with a short period of inhibition. This started about 5 ms after the inhibition of responses evoked by TMS. 5. Recordings in the patients showed that median nerve stimulation reduced the size and number of descending corticospinal volleys evoked by magnetic stimulation. 6. We conclude that mixed or cutaneous input from the hand can suppress the excitability of the motor cortex at short latency. This suppression may contribute to the initial inhibition of the cutaneomuscular reflex. Reduced spinal excitability in this period could account for the mild inhibition of responses to electrical brain stimulation.

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The aim of the experiments was to investigate the effects of speech on the excitability of corticospinal pathways to human hand muscles. Single transcranial magnetic stimuli were given randomly over the hand area of either the left or right motor cortex of 10 right-handed and 3 left-handed normal volunteers. Electromyographic responses were recorded in the relaxed first dorsal interosseous muscle while the subjects (a) read aloud a piece of text, (b) read silently, (c) spoke spontaneously, or (d) made sounds without speaking. The only consistent effect across subjects occurred during task a, which significantly increased the size of responses evoked in the dominant hand of all subjects, but had either no effect (8 subjects) or a smaller effect in the nondominant hand. Tasks b and d had no reliable effect, whereas task c tended to increase response size in both hands. Control measurements suggest that the effects in task a were caused by changes in cortical rather than spinal excitability. This is the first demonstration of lateralized speech effects on the excitability of cortical arm areas. The results provide a useful adjunct to other tests of cerebral dominance, using only single- rather than repetitive-pulse cortical stimulation.

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Seven patients with cerebrotendinous xanthomatosis (CTX) were studied by electrophysiological techniques. The percentages of abnormalities detected in nerve conduction studies and electroencephalograms were 28-6% (two patients) and 100%, respectively. Patients and methodsElectrophysiological studies were performed in seven patients (six men and one woman) whose ages ranged from 35 to 50 (mean 40 3 years). The diagnosis of CTX was established from clinical manifestations and biochemical abnormalities. The subjects in cases 3 and 4 were siblings; the others were sporadic cases. The clinical features of and laboratory findings in patients will be described in detail in a separate report."' We also examined two heterozygote subjects (the mothers of the patients in cases 3 and 4 and in case 5), who showed no clinical manifestations. Serum cholesterol and cholestanol concentrations were determined by high performance liquid chromatography,'2 and the ratio of cholestanol to cholesterol concentration (%) was calculated. The ratio was raised in patients with CTX (1-93 (0-78)) compared with normal controls (0 15 (0-06)) and two carriers (0 13 and 0 15).Motor nerve conduction velocities (MCVs) were measured in the median, posterior tibial, and common peroneal nerves. Sensory nerve conduction velocities (SCVs) were measured in the median, sural, and superficial peroneal nerves.We investigated the short latency somatosensory evoked potentials (SSEPs).