Visual pathways involvement in clinically isolated syndrome in children

AIM: To investigate extent and nature of visual pathways involvement in children with clinically isolated syndrome(CIS).METHODS: Forty-seven patients(age 11-17y) with CIS, which later proved to be multiple sclerosis(MS)onset, and 30 controls underwent visual evoked potentials(VEP) investigation within 12 d from the appearance of the first signs of disease. Latency and amplitude of P100 peak were compared with normative data and between groups.RESULTS: In 58% patients, including those without signs of retrobulbar neuritis, significant slowing of conduction along the central visual pathways(P100latency lengthening) is seen. P100 amplitudes drop(signs of axonal damage) are registered less frequently(29% cases).CONCLUSION: The results indicate that visual pathways are often affected in the MS onset; mostly demyelination signs are seen. Despite MRI significance for MS diagnostic, VEPs proved to be still effective in early diagnosis of MS in children.

Deficits in Magnocellular Pathway in Developmental Dyslexia: A Functional Magnetic Resonance Imaging-Electroencephalography Study

Background: Magnocellular deficit theory is among the different hypotheses that have been proposed to explain the pathophysiology of developmental dyslexia (DD). Dysfunction of the magnocellular system in DD has been investigated using mainly visual evoked potentials (VEPs), particularly transient VEPs, although recently abnormal steady-state VEPs have also been reported. The brain regions responsible for the abnormal VEPs in DD have yet to be elucidated, however. In this study, we performed functional magnetic resonance imaging and electroencephalography (fMRI-EEG) simultaneously to elucidate the brain areas that were found in a previous study to be activated through stimulation of the magnocellular system, and then investigated the mechanism involved in the dysfunction seen in DD.Methods: Subjects were 20 healthy individuals (TYP group;13 men, 7 women;mean ± standard deviation age, 26.3 ± 5.53 years) and 2 men with DD (aged 42 and 30 years). Images of brain activity were acquired with 3-Tesla MRI while the viewing the reversal of low-spatial frequency and low-contrast black-and-white sinusoidal gratings. EEG was recorded concurrently to obtain steady-state VEPs.Results: Stimulus frequency-dependent VEPs were observed in the posterior region of the brain in the TYP group;however, VEP amplitudes in both DD patients were clearly smaller than those in TYP. fMRI images revealed that both the primary and secondary visual cortices were activated by black-and- white sinusoidal gratings in the TYP group, whereas activity in the visual cortex overall was reduced in both DD patients.Conclusions: Present low spatial and high reversal frequency visual stimuli activated the primary visual cortex presumably through predominant activation of the magnocellular pathway. This finding indicates that some cases of adult patients of DD involve impairment of the visual magnocellular system.

Electrophysiological Evidence against the Magnocellular Deficit Theory in Developmental Dyslexia

Over the last two decades, the hypothesis of a magnocellular deficit in dyslexia has raised considerable interest and controversy. Using an electrophysiological procedure (visual evoked potentials, VEP), we compared magnocellular and parvocellular contrast and spatial frequency-response functions between phonological dyslexics (n = 16) and a typical reading group (n = 12) matched for age and socioeconomic background. No significant differences were found between the two groups in the amplitude of the VEP components associated with either magnocellular or parvocellular responses. However, topographic analyses revealed a group difference in the distribution of amplitude in the right frontal and left temporal regions, which appeared to be underactivated in dyslexics. These results suggest a deficit in the higher-level cortical regions involved in phonological and/or linguistic processing, and calls into question the notion of a magnocellular involvement in dyslexia.

重症肌无力患者图形翻转视觉诱发电位的研究

目的；了解重症肌无力（ＭＧ）是否存在视觉传导通路的损害。方法：对２８例ＭＧ患者和３０名年龄与之匹配的正常人进行图形翻转视觉诱发电位（ＰＲＶＥＰ）的检测．结果：ＭＧ组５５只眼检查有３２只眼存在视觉传导功能异常。ＭＧ组Ｐ１００波潜伏期（ＰＬ）和波幅（ＡｍＰ）较正常对照组显著延长或降低。ＭＧ Ｐ１００波ＰＬ和 Ａｍｐ的改变与病情的轻重密切相关．而与年龄和性别无关。１０例复查结果表明，吡啶斯的明＋地塞米松或强的松治疗能明显改善ＰＲＶＥＰ。结论：ＭＧ可出现视觉传导通路的损害，可通过 ＰＲＶＥＰ早期发现之，并且 ＰＲＶＥＰ有可能成为 ＭＧ疗效监测的一种手段。