Response of mammalian gravity receptors to sustained tilt.

I T HAS BEEN demonstrated that subjective responses to prolonged angular accelerations may diminish in amplitude, even though the stimulus persists and the output of the sense organ theoretically increases in magnitude, a These observations indicate that vestibular responses are made primarily to transient accelerations and that considerable adaptation occurs if the stimuli are extended o~er time. Some of this decay can be attributed to changes in the sensory side of the stimulusresponse system. It is known that the projections of the horizontal ampulla in the medial vestibular nucleus do not maintain their responses to extended angular accelerations and that the decay of response is at least partially attributable to central neural activity3 Lowenstein and Roberts 4 have reported some decay in the response of isolated elasmobranch gravity receptors. Adrian 1 found some decline of the response to prolonged tilt, presumably in the medial vestibular nucleus in cat. In these cases, however, this decline was mentioned only incidentally. This study was selected as a starting point for studies of vestibular adaptation for two reasons: (1) technical simplicity in operative procedures and in the maintenance of a vestibular stimulus, and (2) a desire to determine if nuclear vestibular responses unadulterated by cutaneous and proprioceptive and ocher infringements are subject to modification over time r provided the stimulus is held constant. In this study, the stimulus was prolonged tilt at a constant angle. In a practical situation, the stimulus could be steady-state weightlessness.