Original articleStepwise decrease in VEP latencies and the process of myelination in the human visual pathway
Introduction
Myelination is a most fascinating developmental process in the developing brain. One type of glial cell, the oligodendrocyte, is mainly responsible for this process. Oligodendrocytes produce two unique hydrophobic proteins, myelin basic protein (MBP) and proteolipid protein. They wrap axons tightly with these special proteins and lipids. From post-mortem anatomical studies using an immunostaining method for MBP 1, 2and from electron microscopy studies [3], direct information about myelination in the developing human brain has been obtained. Recently, magnetic resonance imaging (MRI) has been introduced in preterm infants 4, 5, 6as well as in term neonates 7, 8to assess the progress in myelination in vivo. MRI detects the accumulation of the substances which are necessary for the components of the myelin sheath, and it also detects a decrease of water content 4, 5, 8. There is a time lag between the initiation of myelination and its detectability using T1-weighted images [9].
For the functional assessment of myelination electroneurophysiological techniques seem most suitable. Longitudinal studies of brainstem auditory evoked potentials and somatosensory evoked potentials in preterm infants have been reported. These studies demonstrated a continuous shortening of the peak latencies with maturation 10, 11, 12. Visual information travels a long distance within the central nervous system. This fact may enable us to obtain indirect but functional evidence of the progress in myelination by the study of the changes in the VEP peak latencies.
Using the N1 peak denominations that we proposed recently [13], we observed a specific timing in the rapid decreases of the latencies. These findings may correlate with the progress of myelination in the visual pathway.
Section snippets
Methods
Twenty-two healthy preterm infants of appropriate birth weights for gestational age (GA), who were born at the GAs of 30 weeks 0 day to 31 weeks 0 day, were included in this prospective study. The mean birth weight was 1400±201 g and mean GA was 30.5±0.4 weeks. The GA was assessed by menstrual dates, ultrasound evaluation and postnatal clinical assessment, and doubtful cases were excluded. Infants with neurological problems or anomalies, perinatal infectious diseases and other severe systemic
Results
Since 21 infants out of the 22 had both some `stable weeks' and one or more `acceleration week(s)', the N1a latency decreased not linearly but in a stepwise pattern. Two illustrative examples are presented in Fig. 1Fig. 2. Only one infant (case no. 17) failed to show any `acceleration weeks' but she had 3 consecutive weeks between 33 and 36 weeks PMA in which the latency decreased at 4 ms per week. No infant presented with increases in the latency of 6 ms per week or more.
There were total 48
Discussion
In a previous study from our department [13], it was demonstrated that VEP can reliably be recorded and analyzed in the preterm period. In that study a stepwise decrease in the N1a latencies was observed (Fig. 1, Fig. 2). We speculate that the progressive rapid decreases in the latency may reflect phases with synchronized increases in the myelination of the visual pathway. The timing of the progress in the myelination in different parts of the pathway may thus be detected in vivo using a
Acknowledgements
The authors wish to express profound gratitude to Professor Hugo Devlieger and the neonatal nursing staff. This study is part of the Developmental Neurology Research Project, KU Leuven, Belgium. At present this research project is mainly supported by a grant from the Medical Research Council, Belgium (FGWO) and by a grant of `Kind en Gezin' (Flemish Child Health Organization), Belgium.
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2010, Clinical NeurophysiologyCitation Excerpt :However, to our knowledge, the maturational changes of these components in children aged 6–17 years old have not been well investigated with MEG. Since visual evoked responses correlate to myelination and synaptic transmission (Scherg and Picton, 1991; Tsuneishi and Casaer, 1997), it is more than likely that VEFs change with age. However, due to the development of the brain, the size of the child’s head varies with age.
- 1
S. Tsuneishi is a clinical research fellow supported by a scholarship from an exchange program between the Flemish community of Belgium and Japan, and by the University of Leuven. Present address: Department of Pediatrics, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650, Japan. Fax: +81 78 3716239.