Response characteristics of frog's lagena afferents to natural stimulation

Abstract

1. The activity of first-order lagena neurons has been recorded in the frog (Rana temporaries). In one set of experiments recordings were obtained directly from the lagena nerve (labyrinthic capsule opened) and in a second set they were obtained from the posterior branch of the VIIIth nerve (labyrinthic capsule closed). 2. Lagena neuron responses to changes in vertical head position (roll, pitch) weretonic (23.5%),phasic-tonic (20.6%) andphasic (41.2%). The magnitude of tonic responses depended on the magnitude of the gravitational vector. Phasic responses were proportional to the velocity of change in head position when the preparation was tilted either in pitch or roll planes. The peak-firing of most of the units was phase-leading head displacement (40.4°±15.1° at 0.20 Hz±10°) when the animal was rotated sinusoidally in vertical planes. The phase angle with respect to head displacement decreased when the frequency of the sinusoidal stimulus increased. The velocity gain (1.42±0.63 spikes×s−1/deg×s−1) decreased both with the frequency and the amplitude of the sinusoid. 3. Two types of functionally polarized hair cells have been found in the lagena. 4. Afferent lagena neurons did not respond to sinusoidal rotation in the horizontal plane but a few neurons responded to vibrations. 5. Opening of the labyrinth affected the response characteristics of some units while others were not affected. The main difference concerned the dynamic properties of lagena neurons: many were phase-lagging head displacement and, especially for phasic units, the time course of the discharge showed a very long decay.