Uhlig Christian Harm, Dykstra Andrew R, Gutschalk Alexander
Department of Neurology, University of Heidelberg, INF 400, 69120 Heidelberg, Germany.
Department of Neurology, University of Heidelberg, INF 400, 69120 Heidelberg, Germany.
Hear Res. 2016 May;335:25-32. doi: 10.1016/j.heares.2016.02.010. Epub 2016 Feb 17.
Forward suppression at the level of the auditory cortex has been suggested to subserve auditory stream segregation. Recent results in non-streaming stimulation contexts have indicated that forward suppression can also be observed in the inferior colliculus; whether this holds for streaming-related contexts remains unclear. Here, we used cardiac-gated fMRI to examine forward suppression in the inferior colliculus (and the rest of the human auditory pathway) in response to canonical streaming stimuli (rapid tone sequences comprised of either one repetitive tone or two alternating tones). The first stimulus is typically perceived as a single stream, the second as two interleaved streams. In different experiments using either pure tones differing in frequency or bandpass-filtered noise differing in inter-aural time differences, we observed stronger auditory cortex activation in response to alternating vs. repetitive stimulation, consistent with the presence of forward suppression. In contrast, activity in the inferior colliculus and other subcortical nuclei did not significantly differ between alternating and monotonic stimuli. This finding could be explained by active amplification of forward suppression in auditory cortex, by a low rate (or absence) of cells showing forward suppression in inferior colliculus, or both.
听觉皮层水平的前向抑制被认为有助于听觉流分离。最近在非流刺激背景下的研究结果表明，在下丘也能观察到前向抑制；在与流相关的背景下是否也是如此仍不清楚。在这里，我们使用心脏门控功能磁共振成像来检查下丘（以及人类听觉通路的其他部分）对典型流刺激（由一个重复音调或两个交替音调组成的快速音调序列）的前向抑制。第一种刺激通常被感知为单个流，第二种刺激被感知为两个交错的流。在不同的实验中，使用频率不同的纯音或耳间时间差不同的带通滤波噪声，我们观察到与重复刺激相比，交替刺激引起更强的听觉皮层激活，这与前向抑制的存在一致。相比之下，下丘和其他皮层下核在交替刺激和单调刺激之间的活动没有显著差异。这一发现可以通过听觉皮层中前向抑制的主动放大、下丘中显示前向抑制的细胞比例较低（或不存在），或两者来解释。
