Effect of acceleration on cerebellar potentials in birds and its relation to sense of direction.

Abstract

Rotatory and postrotatory cerebellar responses of homing and domestic pigeons and of migratory and sedentary doves have been studied by means of a centrifuge, the speed and plane of rotation of which could be changed at will. No appreciable differences have been found in the rotatory cerebellar responses in all the animals tested. Spindle-like postrotatory discharges, however, are a peculiar response of nearly all the homing pigeons and all the migratory doves tested; only 6–8% of the domestic pigeons and no sedentary doves showed similar afterdischarges. Of the hybrids, nearly half had the same postrotatory electrical activity in the cerebellum. The threshold value of centripetal acceleration to produce postrotatory discharges in homing and migratory birds has been found to be 0.004–0.005 g. Postrotatory responses show temporal summation; repetitive stimuli give more numerous and more ample afterdischarges. Nystagmus or, in general, contraction of the neck muscles, does not influence directly the cerebellar afterdischarges. The latter are present in curarized animals, which show no nystagmus and, in domestic pigeons, nystagmus is not accompanied by cerebellar afterdischarges. When coincident in time, however, nystagmus and cerebellar afterdischarges show at times a tendency to synchronization, through physiological factors, which are discussed. The threshold for afterdischarges has been found to be 1000 times higher than changes in possible geodetic forces involved in orientation. This seems to rule out the Ising hypothesis that geodetic forces may be responsible for direction in migration that, notwithstanding the existence of kinesthetic centers of higher sensitivity, is postulated in migratory animals.