Dynamic analysis of the righting reflex in toads; recovery after hemilabyrinthectomy

Static and dynamic measurements of the righting reflex were performed in intact toads (Bufo arenarum platensis) and at different stages of recovery from hemilabyrinthectomy. Reflex activity was evaluated by the toad's capacity to maintain a horizontal head position while rolled sideways. Static data were obtained from frontal photographs. In dynamic experiments platform position (stimulus) was measured through a potentiometer, while a linear accelerometer glued to the cranium was used to record head tilts. The dynamic study included a linear systems analysis using sinusoids of 0.5-3 Hz with rolls of up to 30° to each side. Hemilabyrinthectomy produced a head tilt towards the lesioned side, and gain decay and phase lag increase in the dynamic response. All postural defects recovered progressively within 30-60 days as already described in other species. Nevertheless, the tonic head deviation produced by dynamic stimuli of frequencies above 1 Hz did not recover. This remnant defect has not been observed in previous studies in which only static observations were performed. The involvement of a frequency-dependent rectifying mechanism in postural compensation is discussed.