1,721,209 research outputs found
Characterizing somatosensory evoked potential sources with dipole models: advantages and limitations
No full textSeveral methods have been developed to investigate the cerebral generators of scalp somatosensory evoked potentials (SEPs), because simple visual inspection of the electroencephalographic signal does not allow for immediate identification of the active brain regions. When the neurons fired by the afferent inputs are closely grouped, as usually occurs in SEP generation, they can be represented as a dipole, that is, as a linear source with two opposite poles. Several techniques for dipolar source modeling, which use different algorithms, have been employed to build source models of early, middle-latency, and late cognitive SEPs. Modifications of SEP dipolar activities after experimental maneuvers or in pathological conditions have also been observed. Although the effectiveness of dipolar source analysis should not be overestimated due to the intrinsic limitations of the approach, dipole modeling provides a means to assess SEPs in terms of cerebral sources and voltage fields that they produce over the head
[Familial amyloid polyneuropathy. Description of 2 cases treated with dimethylsulfoxide].
No full textMultiperspective follow-up of untreated carpal tunnel syndrome: A multicenter study
No full textObjective: To assess the course of untreated carpal tunnel syndrome (CTS). Methods: The Italian CTS Study Group prospectively followed up (10 to 15 months) 196 untreated patients (274 hands) with idiopathic CTS with multiple measurements of CTS. Baseline factors were used to predict the evolution of untreated CTS in multiple regression analysis. Results: Comparison of baseline and follow-up data showed a significant spontaneous improvement of patient-oriented and neurophysiologic measurements. A significant correlation between evolution and initial severity of CTS was observed. CTS measurements improved in patients with more severe initial impairment whereas they worsened in patients with milder initial impairment. The main positive prognostic factor was short duration of symptoms. Similarly, spontaneous improvement was more frequently associated with young age. Conversely, baseline bilateral symptoms and positive Phalen predicted a poor prognosis. Conclusions: Some patients with CTS improve spontaneously without surgical treatment
Functional properties of human thymoma lymphocytes: role of subcellular factors in blastic activation.
No full text"Dropping objects": a potential index of severe carpal tunnel syndrome
No full textPatients affected by carpal tunnel syndrome (CTS) often report finding themselves "dropping objects". This symptom is perceived as a severe and frustrating problem. We investigated the occurrence of "dropping objects" in a sample of 532 patients affected by CTS, studied with a multidimensional protocol (clinical, neurophysiological, and patient-oriented). To ensure that the definition of "dropping objects" was index of abnormality, we evaluated a control group interviewing 200 subjects. In order to evaluate if "dropping objects" was an index of more severe CTS impairment, we compared the severity measures between the patients with and without this condition. Severity of CTS multidimensionally assessed was significantly greater in patients with a history of dropped objects than those without. Moreover, "dropping objects" was more frequent in females, older patients, and in those patients with more functional impairment. The occurrence of "dropping objects" in CTS patients seems to be an index of CTS severity
Parietal generators of low- and high-frequency MN (median nerve) SEPs: data from intracortical human recordings
No full textObjective: to identify low and high-frequency median nerve (MN) somatosensory evoked potential (SEP) generators by means of chronically implanted electrodes in the parietal lobe (SI and neighbouring areas) of two epileptic patients. Methods: wide-pass short-latency and long-latency SEPs to electrical MN stimulation were recorded in two epileptic patients by stereotactically chronically implanted electrodes in the parietal lobe (SI and neighbouring areas). To Study high-frequency responses (HFOs) an off-line digital filtering of depth short-latency SEPs was performed (500-800 Hz, 24 dB roll-off). Spectral analysis was performed by fast Fourier transform. Results: in both patients we recorded a N20/P30 potential followed by a biphasic N50/P70 response. A little negative response in the 100 iris latency range was the last detectable wide-pass SEP in both patients. Two HFOs components (called iP1 and iP2) were detected by mere visual analysis and spectral analysis, and were supposed to be originated within the parietal cortex. Conclusions: this was the very first Study that recorded wide bandpass and high frequency SEPs by electrodes, exploring both the lateral and the mesial part of the parietal lobe and particularly that of the post-central gyrus
Selective abnormality of the N13 spinal SEP to dermatomal stimulation in patients with cervical monoradiculopathy
No full textScalp somatosensory evoked potentials (SEP) to dermatomal stimulation have so far proved to be only partially useful in the diagnosis of monoradiculopathy, mostly in cases without motor impairment. The aim of our study was to test the sensitivity of the spinal N13 potential in uncovering lesions of single cervical roots. We studied five patients suffering from cervical monoradiculopathy, using a recording technique allowing specific recording of the genuine N13 potential which is probably generated by dorsal horn cells. No patient showed signs of muscle impairment and needle EMG was always normal. In four patients, the N13 SEP was, absent following stimulation of the dermatome corresponding to the damaged root, while both the lemniscal P14 and the cortical N20 components were normal. SEP recorded after stimulation of upper limb troncular nerves showed no abnormality in all patients. Our findings suggest that the N13 potential, the loss of which after dermatomal stimulation could be due to deafferentation of dorsal horn neurones, is particularly sensitive to initial root compression. Therefore, our montage allowing analysis of the genuine N13 SEP can improve the sensitivity of dermatomal SEP recording in patients with cervical monoradiculopathies
Central scalp projection of the N30 SEP source activity after median nerve stimulation
Full text linkConflicting results have been reported about abnormalities of the N30 somatosensory evoked potential (SEP) in movement disorders. In these studies, the N30 amplitude was measured in the frontal scalp region. Our aim was to identify the scalp electrodes recording the genuine activity of the N30 generator. In 18 subjects, we recorded the scalp SEPs from 19 electrodes and found a negative potential around 30 ms reaching its maximal amplitude in the frontal region. However, neither simple visual inspection of the frontal traces nor topographic analysis could distinguish the N24 from the N30 component of the frontal negativity. Brain electrical source analysis of SEPs showed that a four dipolar source model could well explain the scalp SEP distribution. We calculated the scalp field distributions of the source activities as modeled from the scalp recordings and observed that the maximal field distribution reflecting the activity of the N30 source was in the central region, whereas that reflecting the N24 source activity was frontal. We conclude that the negative response recorded around 30 ms in the central traces represents "genuine" N30 source activity, whereas the frontal negativity, which is higher in amplitude, is a mixture of the activities of both the N30 and N24 sources. (C) 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 353-360, 2000
Distinct fronto-central N60 and supra-sylvian N70 middle-latency components of the median nerve SEPs as assessed by scalp topographic analysis, dipolar source modelling and depth recordings
No full textobjectives: to investigate the possible contribution of the second somatosensory (SII) area in the generation of the N60 somatosensory evoked potential (SEP).Methods: In 7 epileptic patients and in 6 healthy subjects scalp SEPs were recorded by 19 electrodes placed according to the 10-20 system. all epileptic patients but one were also investigated using depth electrodes chronically implanted in the parieto-rolandic opercular cortex. Scalp SEPs underwent brain electrical source analysis. results: In both epileptic patients and healthy subjects, scalp recordings showed two middle-latency components clearly distinguishable on the basis of latency and scalp distribution: a fronto-central N60 potential contralateral to stimulation and a later bilateral temporal N70 response. SEP dipolar source modelling showed that a contralateral perisylvian dipole was activated in the scalp N70 latency range whereas separate perirolandic and frontal sources were activated at the scalp N60 latency. depth electrodes recorded a biphasic N60/P90 response in the parieto-rolandic opercular regions contra- and ipsilateral to stimulation. conclusions: two different middle-latency SEP components N60 and N70 can be distinguished by topographic analysis and source modelling of scalp recordings, the sources of which are located in the fronto-central cortex contralateral to stimulation and in the supra-sylvian cortex on both sides, respectively. the source location of the scalp N70 in the SII area is strongly supported by its spatio-temporal similarities with SEPs directly recorded in the supra-sylvian opercular cortex
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