1,720,979 research outputs found
Effect of repetition rate on middle latency auditory evoked potentials in humans
No full textMiddle Latency Auditory Evoked Potentials (MLAEPs) were recorded from 15 healthy subjects in order to evaluate the influence of different repetition rates on the latency and the amplitude of their main components Na, Pa and Nb. MLAEPs were obtained from Cz-ipsilateral ear lobe by averaging responses to 2000 monaural clicks delivered to both ears, at 65 dB SL of intensity, for each of 3 different repetition rates (1.1, 4.1, 8.1 Hz). Time base was 100 ms, analogical band-pass filter 5-1000 Hz (off-line digital bandpass: 20-100 Hz). The statistical analysis (repeated measures analysis of variance), demonstrated that, the latency and the amplitude of the Nb component were slightly influenced by repetition rate while Pa and Na were not. Moreover Nb showed the greatest interindividual variability (as already pointed out by other authors too); thus, we suggest that a stimulus rate of 8.1 Hz and the analysis of Na and Pa component only, can be regarded as the best assessment for MLAEPs evaluation when they are used for clinical purposes
Edge detection and surface filling-in as shown by texture visual evoked potentials
No full textObjectives: We designed a stimulation paradigm that was designed to ascertain whether specific components of the texture visual evoked potentials were attributable to edge detection or to surface 'filling-in' processes. Methods: The stimuli were textures of parallel line elements, which were either uniform (all horizontal or vertical lines) or segregated (checkerboards in which texture line elements of neighbor checks were oriented orthogonally). A sequence of 4 stimuli, two uniform followed by two segregated stimuli, was repeated cyclically. Accordingly, segregation could appear from a uniform display; it could also be maintained, with the checkerboard illusory margin location unchanged but with alteration in the orientation of all line elements. Each stimulus was presented for 487 ms and instantly replaced by the following one. Results: Segregation-related components for segregation-appearance (Sa) and for segregation-maintenance (Sm) conditions were obtained separately by subtraction. In both conditions, a negative component was obtained with a peak latency of about 140-150 ms. However, the onset of Sa was earlier than that of Sm, whereas the respective offsets were almost identical. Conclusions: We hypothesize that the segregation component in VEPs is composed of two subcomponents: an early part, which is related to the segregation of edges, and a final part, which is related to the 'filling-in' of the homogneous texture surface within the boundary defined by these edges
Visual evoked potentials in the white New Zealand rabbit: source localization and normative aspects
No full textNormative data of visual evoked potentials were obtained from occipital screw electrodes referenced to a nasal electrode in 10 white New Zealand rabbits. Two time-bases were used (200 and 400 ms) in order to reliably identify both early components (of retinal and cortical origin), as well as late components. The putative origin of the single components was established by simultaneous recording of ERG and by stereotaxic recordings from the lateral geniculate body. Test-retest variability was measured repeating the recordings after 24 hours
Multimodal evoked potentials in diabetics
No full textIn the present study we performed brainstem auditory evoked potentials, pattern electroretinogram and visual evoked potentials for the identification of a subclinical involvement of central auditory and visual pathways in diabetes mellitus. We tested 30 patients, and a neurophysiological central nervous system involvement was demonstrated in 23.3% of them. The mean values of patients and controls were significantly different for most of the evoked potential parameters. Some of these parameters were linearly related with duration of the disease, clinical score and peripheral nerve conduction velocities
Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters
No full textTwenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences
Middle latency auditory evoked potentials improve the detection of abnormalities along auditory pathways in multiple sclerosis patients
No full textA one-week test-retest reliability study of Brainstem Auditory Evoked Potentials
No full textBrainstem Auditory Evoked Potentials (BAEPs) are increasingly used in longitudinal evaluation of brainstem function. The reliability of the neurophysiological parameters and definition of the normal test-retest variability are required for such investigations. In the present study we submitted 20 healthy volunteers (10 males and 10 females; mean age 35.1 years, range 24-49) to BAEPs in two sessions separated by seven days. The reliability of the parameters was estimated by means of intraclass correlation coefficient (R). All BAEP parameters showed excellent R values (above 0.75). In addition, the confidence interval lower limits of all R coefficients had good to excellent values. Finally we computed the upper normal limits of the test-retest variability of each parameter, with alpha = 0.01, using the within-subjects mean square. The confirmed good reliability of the analyzed parameters enables us to employ BAEPs as useful monitoring instruments in longitudinal studies
Somatosensory evoked potentials by median nerve stimulation recorded with cephalic and non-cephalic references. I). Normative study
No full textSomatosensory evoked potentials by median nerve stimulation were obtained in 50 healthy subjects (aged 15-70 years) with cephalic and non cephalic references. Most parameters were influenced by one or more independent variables (sex, age, arm lengths). The coefficients of the appropriate linear models are reported to compute correct individual normal limits
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