[The effect of age on inhibition of visual fixation of the rotatory-induced nystagmus reaction].

The interactive functions between sensory systems show changes that depend on the development of the growing body. Important conditions for the development of the visual suppression of vestibular evoked nystagmus reactions are the maturation of the visual system, the presence of a functioning vestibular system and close connections between both systems. Response to vestibular, visual and combined vestibular and visual stimulation does not only change during early childhood. We have also learnt from studies of adults of different ages that there are characteristic changes in nystagmus reactions to vestibular stimulation, in optokinetic reactions and in vestibular-spinal functions during the whole period of life. 272 randomly selected neuro-otologic routine patients aged between one year and four months and eighty-eight years and ten months were included in the study to analyse age-related changes of visual suppression during rotatory stimulation. The rotatory stimulation consisted of an sinusoidal stimulus pattern with amplitudes of +/- 180 degrees and a period duration of 20s. The vestibular stimulation was performed in total darkness and with a visual target which was attached to the chair in front of the patient's eyes. The results of this study demonstrate that the amplitudes of nystagmus reactions, evoked by sinusoidal harmonic acceleration, can be quantitatively suppressed by visual fixation. The degree of suppression depends on age. The fixation indices provide the ability to measure the degree of this suppression in percent. The trend to better fixation suppression increases up to the end of the age of forty. The ability to suppress vestibular nystagmus decreases, however, after reaching the fortieth year of life. The analysis of smooth pursuit shows after the sixtieth year of life a continuous rise in the number of saccades with increasing age. These changes are caused by aging processes in cerebral tissues which lead to functional changes e.g. in the interactive functions between sensory systems.