Transcranial magnetic-evoked potentials under total intravenous anaesthesia and nitrous oxide.
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Magnetic stimulation of the cortex and recording of the motor-evoked potentials (MEPs) by electromyography (EMG) is a well proven method to assess the descending pathways of the spinal cord and detect neurological impairment. We have assessed, in 33 adult patients undergoing spinal surgery, the influence of four total i.v. anaesthesia regimens (TIVA) on this recording technique. In 20 patients, the effect of 50% nitrous oxide was also studied. MEP amplitudes, latencies and success rates of stimulation were obtained in the steady-state after induction of anaesthesia. Combinations of midazolam and ketamine, and alfentanil and etomidate had the least effect on MEPs. Propofol (in combination with alfentanil or ketamine) showed marked depression of the MEP amplitude and the lowest success rates of stimulation. The latencies did not change at all. The addition of nitrous oxide significantly depressed the registered MEPs and lowered the success rates. (+info)
Interactions between two different inhibitory systems in the human motor cortex.
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Intracortical inhibition in the human motor cortex has been previously demonstrated using paired-pulse transcranial magnetic stimulation (TMS) protocols at short intervals (1-6 ms; short interval intracortical inhibition, SICI) with a subthreshold conditioning pulse preceding a suprathreshold test pulse, and at long intervals (50-200 ms; long interval intracortical inhibition, LICI) with suprathreshold conditioning and test pulses. We investigated whether different circuits mediate these inhibitory phenomena and how they interact. In nine healthy volunteers, we applied TMS to the motor cortex and recorded motor evoked potentials from the first dorsal interosseous muscle. With increasing test pulse strength, LICI decreases but SICI tends to increase. There was no correlation between the degree of SICI and LICI. We tested the interactions between SICI and LICI. SICI was reduced or eliminated in the presence of LICI. Loss of SICI was seen even with a conditioning stimulus too weak to induce significant LICI. Our findings demonstrate that different cell populations mediate SICI and LICI. The results are consistent with the hypothesis that LICI inhibits SICI through presynaptic GABAB receptors. Testing of SICI in the presence of LICI may be a non-invasive way of evaluating inhibitory interactions in the human motor cortex. (+info)
Abnormalities of sensorimotor integration in focal dystonia: a transcranial magnetic stimulation study.
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It has been postulated that sensorimotor integration is abnormal in dystonia. We investigated changes in motor cortical excitability induced by peripheral stimulation in patients with focal hand dystonia (12 patients with hand cramps) and with cervical dystonia (nine with spasmodic torticollis) compared with 16 age-matched normal controls. Motor evoked potentials (MEP) to focal (figure-of-eight coil) transcranial magnetic stimulation of the hand area were recorded from the right abductor pollicis brevis (APB), first dorsal interosseus (FDI), flexor carpi radialis and extensor carpi radialis muscles. Changes of test MEP size following conditioning stimulation of the right median nerve (or of the index finger) at conditioning-test (C-T) intervals of 50, 200, 600 and 1000 ms were analysed. Peripheral stimulation significantly reduced test MEP size in the APB and FDI muscles of normal control and spasmodic torticollis patients. The inhibitory effect was larger upon median nerve stimulation and reached a maximum at the C-T interval of 200 ms. On the contrary, hand cramp patients showed a significant facilitation of test MEP size. This study suggests that MEP suppression following peripheral stimulation is defective in patients with focal hand dystonia. Central processing of sensory input is abnormal in dystonia and may contribute to increased motor cortical excitability. (+info)
Transcranial magnetic stimulation and stretch reflexes in the tibialis anterior muscle during human walking.
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Stretch of the ankle dorsiflexors was applied at different times of the walking cycle in 17 human subjects. When the stretch was applied in the swing phase, only small and variable reflex responses were observed in the active tibialis anterior (TA) muscle. Two of the reflex responses that could be distinguished had latencies which were comparable with the early (M1) and late (M3)components of the three reflex responses (M1, M2 and M3) observed during tonic dorsiflexion in sitting subjects. In the stance phase a single very large response was consistently observed in the inactive TA muscle. The peak of this response had the same latency as the peak of M3, but in the majority of subjects the onset latency was shorter than that of M3. The TA reflex response in the stance phase was abolished by ischaemia of the lower leg at the same time as the soleus H-reflex, suggesting that large muscle afferents were involved in the generation of the response. Motor-evoked potentials (MEPs) elicited in the TA by transcranial magnetic stimulation (TMS) were strongly facilitated corresponding to the peak of the stretch response in the stance phase and the late reflex response in the swing phase. A similar facilitation was not observed corresponding to the earlier responses in the swing phase and the initial part of the response in stance. Prior stretch did not facilitate MEPs evoked by transcranial electrical stimulation in the swing phase of walking. However, in the stance phase MEPs elicited by strong electrical stimulation were facilitated by prior stretch to the same extent as the MEPs evoked by TMS. The large responses to stretch seen in the stance phase are consistent with the idea that stretch reflexes are mainly involved in securing the stability of the supporting leg during walking. It is suggested that a transcortical reflex pathway may be partly involved in the generation of the TA stretch responses during walking. (+info)
Phrenic nerve conduction and diaphragmatic motor evoked potentials: evaluation of respiratory dysfunction.
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OBJECTIVE: To investigate preliminarily the value of phrenic nerve conduction (PNC) and diaphragmatic motor evoked potentials (MEPs) in the evaluation of various respiratory dysfunction (RDF). METHODS: Thirty-four patients with various RDF, (19 patients with neurogenical diseases and 15 patients with respiratory disorders) were investigated. Fifty healthy volunteers served as controls. The phrenic nerve was cutaneously stimulated by electrical pulse current at the midpoint of the posterior border of the sternomastoid muscle, and the diaphragmatic muscle compound action potentials (DCAP) were recorded between the 7th and 8th intercostal space and xiphoid process. When the magnetic transcranial stimulation (MTS) of the cortex was given, the recordings were made under the condition of maximal deep inspiration. RESULTS: All patients with myopathies had normal PNC. The patients with Guillain Barre syndrome (GBS), hereditary motor and sensory neuropathy (HMSN) and myasthenic crisis had abnormal PNC. The findings in PNC studies remarkably correlated with RDF, while serial examinations were performed in the patients with GBS and myasthenia gravis (MG). In 7 patients with sleep apnea syndrome (SAS), 4 had abnormal PNC, and 2 of 3 patients with chronic obstructive pulmonary diseases (COPD), and 1 of 5 patients with chest tightness or breathlessness on the supine position showed decreased amplitude. When MEPs were recorded, 3 of 5 patients showed abnormal SAS (1 had no response, 2 lower amplitude). Three patients with COPD had normal MEP. CONCLUSIONS: PNC studies could not only evaluate neuromuscular RDF and predict the outcome of diseases, but also supply additional information about diaphragmatic dysfunction for the RDF caused by respiratory disorders. The results of PNC and diaphragmatic MEP may differentiate the types of SAS. (+info)
Application of pudendal evoked potentials in diagnosis of erectile dysfunction.
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AIM: Extensive neurophysiological investigations were carried out in 100 healthy subjects and 84 patients with penile erectile dysfunction. METHODS: Following examinations were performed, spinal and scalp somatosensory evoked potentials (SEPs) to stimulation of the dorsal nerve of penis, motor evoked potentials (MEPs) from bulbocavernosus (BC) in response to scalp and spinal root stimulation, and measurement of sacral reflex latency (SRL) from anal sphincter (AS). RESULTS: In the healthy subjects, the mean sensory total conduction time (sensory TCT), as measured at the peak of the scalp P1 (P40) wave was 39.73 ms. The mean sensory central conduction time (sensory CCT = spinal-to-scalp conduction time) was 28.98 ms. The mean peripheral conduction time (PCP) was 9.40 ms. Transcranial brain stimulation was performed by using a magnetic stimulator during voluntary contraction of the examined muscle. Spinal root stimulation was performed at rest. Motor total conduction time (motor TCT) to BC muscles was 20.48 ms. Motor central conduction time (motor CCT) to sacral cord segments controlling BC muscles was 14.42 ms at rest. The mean SRL was 35.13 ms. CONCLUSION: Combined or isolated abnormalities of SEPs, MEPs, and SRL were found in patients with erectile dysfunction. (+info)
Excitatory and inhibitory corticospinal responses to transcranial magnetic stimulation in patients with minor to moderate head injury.
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OBJECTIVES: The changes in excitatory and inhibitory responses to transcranial magnetic stimulation (TMS), as attested by motor evoked potential (MEP) and silent period (SP) parameters, were compared in patients who sustained minor to moderate head injury. METHODS: A total of 38 patients with brain concussion, and diffuse, focal, and combined brain injury and 20 healthy volunteers were examined. The MEPs and SPs were recorded from the abductor pollicis brevis muscle after single pulse TMS 2 weeks after head trauma. The parameters assessed were the MEP resting threshold, the MEP/M wave amplitude ratio, the central motor conduction time (CMCT), the SP threshold, the interthreshold difference (ITD), and the SP duration (SPD). RESULTS: The main finding was an increase in the ITD in patients with mild and moderate head injury due to the relatively greater augmentation of the MEP threshold. This was associated with a reduction of the MEP/M wave amplitude ratio. The degree of MEP and SP changes depended on severity of head injury and was not related to the type of brain lesions. The SPD did not differ significantly in brain concussion, or diffuse, focal and combined brain injury groups compared with the control group. The CMCT was prolonged in patients with diffuse and combined brain lesions. Among subjective complaints only fatigue was significantly related to ITD, MEP, and SP threshold abnormalities. CONCLUSIONS: The results suggest that mechanisms involved in MEP and SP generation are differently affected in head injury, the first being impaired more severely. The increase of the ITD accompanied by reduction of the MEP/M wave amplitude ratio may reflect a dissociated impairment of inhibitory and excitatory components of central motor control in head trauma. (+info)
Functional brain imaging based on ERD/ERS.
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Sensory, cognitive and motor processing can result in changes of the ongoing EEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). Both phenomena are time-locked but not phase-locked to the event and they are highly frequency-band specific. The ERD is interpreted as a correlate of an activated cortical area with increased excitability and the ERS in the alpha and lower beta bands can be interpreted, at least under certain circumstances, as a correlate of a deactivated cortical area. Spatial mapping of ERD/ERS can be used to study the dynamics of cortical activation patterns. Examples from a movement task are reported. (+info)