Development of the dynamic characteristics of the horizontal vestibulo-ocular reflex in infancy.

The horizontal vestibulo-ocular reflex (VOR) has been recorded electrooculographically in normal infants aged from one to four weeks and in older subjects submitted to sinusoidal oscillations (+/- 15 degrees, 0.05-0.5 Hz) in the dark. The analysis of the dynamic characteristics of the reflex indicates that, at least in the low frequency range, the VOR has not yet attained a truly compensatory role in the first month of life. In two of the subjects the VOR has been followed throughout the second month of life. At this age the phase of the reflex has already developed the characteristics of the comparison-group at all the frequencies of stimulation, while the trend of the amplitude modulation has not yet changed from the newborn stage. By the 6th month of life the VOR characteristics are comparable with those present in the comparison-group. It appears therefore that the horizontal VOR undergoes a process of maturation during the early period of life, which affects in different times both phase and amplitude values. The possible role exerted by different neural structures on this maturation process is discussed.