The superior olivary complex and audition: A comparative study

Abstract

The sizes of the three major nuclei of the mammalian superior olivary complex were examined in a number of different species and variations in size were related to the relative prominence of haring and vision in each species. Size was measured by counting neurons in the several nuclei and by measuring the diameter of the eyes.The lateral superior olive was large inMicrochiroptera(3850–4340 cells), guinea pig (3780), cat (3360) and chinchilla (3220); of intermediate size in macaque (1830), rat (1430) and squirrel monkey (1300); and small in gerbil (1220), mouse (1190), hedgehog (1090), squirrel (1000) and hamster (980). These data suggest that this nucleus is necessary for complex auditory discriminations (echolocation inMicrochiroptera, for example) and that its size is not primarily determined by the taxonomic order of the animal.The medial nucleus of the trapezoid body was large in cat (5910), guinea pig (5840), hedgehog (4620) and chinchilla (4590); of intermediate size in rat (3870),Microchiroptera(3700) and macaque (3120); and small in squirrel monkey (2600), squirrel (2700), gerbil (2680), mouse (2270), and hamster (2130). The size of the nucleus was not related to sensory development or the size of the other olivary nuclei.The size of the medial superior olive was found to be highly correlated with the size of the VIth nucleus and eye diameter.