The auditory brainstem response (ABR) to stimulus onset has been extensively used to investigate dolphin hearing. The mechanisms underlying this onset response have been thoroughly studied in mammals. In contrast, the ABR evoked by sound offset has received relatively little attention. To build upon previous observations of the dolphin offset ABR, a series of experiments was conducted to (1) determine the cochlear places responsible for response generation and (2) examine differences in response morphologies when using toneburst versus noiseburst stimuli. Measurements were conducted with seven bottlenose dolphins (Tursiops truncatus) using tonebursts and spectrally “pink” broadband noisebursts, with highpass noise used to limit the cochlear regions involved in response generation. Results for normal-hearing and hearing-impaired dolphins suggest that the offset ABR contains contributions from at least two distinct responses. One type of response (across place) might arise from the activation of neural units that are shifted basally relative to stimulus frequency and shares commonalities with the onset ABR. A second type of response (within place) appears to represent a “true” offset response from afferent centers further up the ascending auditory pathway from the auditory nerve, and likely results from synchronous activity beginning at or above the cochlear nucleus.

中文翻译：

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宽吻海豚（Tursiops truncatus）的偏移听觉脑干反应：多个潜在过程的证据

对刺激开始的听觉脑干反应 (ABR) 已被广泛用于研究海豚的听力。已经在哺乳动物中彻底研究了这种起始反应的潜在机制。相比之下，由声音偏移引起的 ABR 受到的关注相对较少。为了建立在先前对海豚偏移 ABR 的观察的基础上，进行了一系列实验，以 (1) 确定负责响应生成的耳蜗位置和 (2) 检查使用音爆与噪声爆裂刺激时响应形态的差异。测量是用七只宽吻海豚（Tursiops truncatus) 使用音调突发和频谱“粉红色”宽带噪声突发，使用高通噪声来限制参与响应生成的耳蜗区域。听力正常和听力受损的海豚的结果表明偏移 ABR 包含来自至少两种不同反应的贡献。一种类型的反应（跨位置）可能源于神经单元的激活，这些神经单元相对于刺激频率发生了根本性的变化，并且与 ABR 的发作具有共性。第二种类型的反应（就地）似乎代表了来自传入中枢的“真实”偏移反应，从听觉神经沿上行听觉通路进一步向上，并且可能是由在耳蜗核处或上方开始的同步活动引起的。