Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin.
Department of Neuroscience, Brown University, Providence, Rhode Island.
J Neurophysiol. 2021 Oct 1;126(4):1314-1325. doi: 10.1152/jn.00013.2021. Epub 2021 Sep 8.
Echolocating big brown bats () perceive their surroundings by broadcasting frequency-modulated (FM) ultrasonic pulses and processing returning echoes. Bats echolocate in acoustically cluttered environments containing multiple objects, where each broadcast is followed by multiple echoes at varying time delays. The bat must decipher this complex echo cascade to form a coherent picture of the entire acoustic scene. Neurons in the bat's inferior colliculus (IC) are selective for specific acoustic features of echoes and time delays between broadcasts and echoes. Because of this selectivity, different subpopulations of neurons are activated as the bat flies through its environment, while the physical scene itself remains unchanging. We asked how a neural representation based on variable single-neuron responses could underlie a cohesive perceptual representation of a complex scene. We recorded local field potentials from the IC of big brown bats to examine population coding of echo cascades similar to what the bat might encounter when flying alongside vegetation. We found that the temporal patterning of a simulated broadcast followed by an echo cascade is faithfully reproduced in the population response at multiple stimulus amplitudes and echo delays. Local field potentials to broadcasts and echo cascades undergo amplitude-latency trading consistent with single-neuron data but rarely show paradoxical latency shifts. Population responses to the entire echo cascade move as a unit coherently in time as broadcast-echo cascade delay changes, suggesting that these responses serve as an index for the formation of a cohesive perceptual representation of an acoustic scene. Echolocating bats navigate through cluttered environments that return cascades of echoes in response to the bat's broadcasts. We show that local field potentials from the big brown bat's auditory midbrain have consistent responses to a simulated echo cascade varying across echo delays and stimulus amplitudes, despite different underlying individual neuronal selectivities. These results suggest that population activity in the midbrain can build a cohesive percept of an auditory scene by aggregating activity over neuronal subpopulations.
回声定位的大棕蝠 () 通过广播调频 (FM) 超声波脉冲并处理返回的回声来感知周围环境。蝙蝠在充满多个物体的嘈杂环境中进行回声定位，每个广播后都会有多个回声以不同的时间延迟返回。蝙蝠必须解析这个复杂的回声级联，以形成整个声场景的连贯图像。蝙蝠下丘脑中的神经元对回声和广播与回声之间的时间延迟的特定声学特征具有选择性。由于这种选择性，当蝙蝠在其环境中飞行时，不同的神经元亚群被激活，而物理场景本身保持不变。我们想知道基于可变的单个神经元响应的神经表示如何为复杂场景的凝聚力感知表示提供基础。我们记录了大棕蝠下丘脑中的局部场电位，以检查类似于蝙蝠在植被旁飞行时可能遇到的回声级联的群体编码。我们发现，模拟广播后面跟着回声级联的时间模式在多个刺激幅度和回声延迟下的群体反应中得到忠实再现。广播和回声级联的局部场电位随着与单个神经元数据一致的幅度潜伏期交换，但很少出现反常的潜伏期移位。整个回声级联的群体反应随着广播-回声级联延迟的变化而作为一个整体在时间上协调移动，这表明这些反应是形成声场景凝聚力感知表示的指标。回声定位蝙蝠在杂乱的环境中导航，这些环境会对蝙蝠的广播做出回声级联的反应。我们表明，大棕蝠听觉中脑的局部场电位对模拟回声级联的反应在回声延迟和刺激幅度上都具有一致性，尽管潜在的单个神经元选择性不同。这些结果表明，中脑的群体活动可以通过聚合神经元亚群的活动来构建听觉场景的凝聚力感知。
