Schmitz B, White T D, Narins P M
Department of Biology, University of California, Los Angeles 90024.
J Comp Physiol A. 1992 Jun;170(5):589-604. doi: 10.1007/BF00199335.
A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens. Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6). In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.
采用第八神经背侧入路和自由场刺激来研究声音方向和强度对豹蛙（Rana pipiens pipiens）听神经纤维锁相的影响。分析了75个听觉神经元的调谐曲线（图2）。两栖类乳头神经元而非基底乳头神经元在特征频率（CF）下对短音爆表现出显著的锁相，锁相程度（矢量强度）随神经元的CF降低（图3、4和10E）。矢量强度随声压级增加，在阈值以上约20 dB时达到饱和，而最佳放电相位仅受到轻微影响（图5和6）。相比之下，声音方向对矢量强度影响很小（图7、8、9A和10A及C），但对最佳放电相位有强烈影响（图7、8、9B和C、10B和D）：相对于前方声音呈现，同侧有相位滞后，后方和对侧呈现时有相位超前。两耳之间的相位差呈现正弦或心形/卵形方向特性；在前外侧声音呈现时差异最大（图11）。锁相的方向性随神经元的CF降低（图10F），且随声压级变化很小（图12）。因此，两栖类乳头神经元的锁相可能为声音定位提供与强度无关的信息。
