Abstract
It is known that neonatal development of vision is based on neuronal activity in the visual cortex, and influenced by closing the eyelids during a certain period in neonatal cats. It is obvious that development of vision depends not only on the visual cortex but also upon the perception process of vision. When the visual evoked potentials (VEP) are used to indicate the visual sensation, the primary and secondary evoked potentials are those of the visual cortex and the whole cortex, respectively. In the present experiments, neonatal development of visual sensation was examined by recording both primary and secondary evoked potentials. VEP were recorded through cranial surface plate bipolar electrodes between Pz and Inion, corresponding to regions of the ten-twenty Recording Methods for electroencephalogram. A flash of light was applied through a hole in the top of the box. Unanesthized and unrestricted animals were put into the box. The secondary VEP was identified from the primary VEP with a latency of about 100 msec. It is well known that primary and secondary VEPs reach the visual cortex via a specific projection system and of the whole cortex via a non-specific projection system, respectively. Since it was reported that development of visual cortex neuronal activity was profoundly influenced by eyelid closure during the critical period, a few days in the begining of the fourth week after birth, three kinds of the eyelids closure were performed in the present experiments. Eyelids were closed 1) at 2 weeks after birth for 2 weeks, 2) at 4 weeks after birth for 3 or 7 weeks, and 3) at 2 weeks after birth for 4 weeks. Primary VEP appeared 2.5 weeks after birth, developed gradually, reached the maximum 5 weeks after birth and then remained stable. The secondary VEP was unstable, depending on the state of the animal, during the 12 weeks of the experimental period. Development of the primary VEP was transiently depressed, but it was evoked during eyelid closure and gradually developed to the control level after the eyelids were opened. On the other hand, the secondary VEP was not induced during eyelid closure. In eyelid closures 1) and 2), the reappearing of the secondary VEP after the eyelids were opened was very slow, but it recovered to control level 50-120 days later. In eyelid closure 3) the secondary VEP never recovered after the eyelids were opened. It was concluded that secondary VEP was strongly influenced and did not recover after eyelids closure at 2 weeks after birth for 4 weeks. It was estimated that the perception process was more influenced by eyelid closure than the visual cortex process.
