Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
J Exp Biol. 2013 Jul 1;216(Pt 13):2393-402. doi: 10.1242/jeb.082321.
Natural sensory stimuli have a rich spatiotemporal structure and can often be characterized as a high frequency signal that is independently modulated at lower frequencies. This lower frequency modulation is known as the envelope. Envelopes are commonly found in a variety of sensory signals, such as contrast modulations of visual stimuli and amplitude modulations of auditory stimuli. While psychophysical studies have shown that envelopes can carry information that is essential for perception, how envelope information is processed in the brain is poorly understood. Here we review the behavioral salience and neural mechanisms for the processing of envelopes in the electrosensory system of wave-type gymnotiform weakly electric fishes. These fish can generate envelope signals through movement, interactions of their electric fields in social groups or communication signals. The envelopes that result from the first two behavioral contexts differ in their frequency content, with movement envelopes typically being of lower frequency. Recent behavioral evidence has shown that weakly electric fish respond in robust and stereotypical ways to social envelopes to increase the envelope frequency. Finally, neurophysiological results show how envelopes are processed by peripheral and central electrosensory neurons. Peripheral electrosensory neurons respond to both stimulus and envelope signals. Neurons in the primary hindbrain recipient of these afferents, the electrosensory lateral line lobe (ELL), exhibit heterogeneities in their responses to stimulus and envelope signals. Complete segregation of stimulus and envelope information is achieved in neurons in the target of ELL efferents, the midbrain torus semicircularis (Ts).
自然感觉刺激具有丰富的时空结构，通常可以被描述为一种高频信号，该信号可以在较低频率下独立调制。这种低频调制称为包络。包络常见于各种感觉信号中，例如视觉刺激的对比度调制和听觉刺激的幅度调制。虽然心理物理学研究表明，包络可以携带对感知至关重要的信息，但大脑如何处理包络信息还知之甚少。在这里，我们回顾了电感受系统中包络处理的行为显著性和神经机制，电感受系统存在于波型电鳗型弱电鱼中。这些鱼可以通过运动、它们在社会群体中的电场相互作用或通信信号产生包络信号。前两种行为背景产生的包络在频率内容上有所不同，运动包络通常频率较低。最近的行为证据表明，弱电鱼会以稳健和刻板的方式对社会包络做出反应，以增加包络频率。最后，神经生理学结果显示了包络是如何被外周和中枢电感受神经元处理的。外周电感受神经元对刺激和包络信号都有反应。这些传入神经的初级后脑接收者，即电感受侧线叶（ELL）中的神经元，对刺激和包络信号的反应存在异质性。在 ELL 传出神经的靶标，中脑半规管（Ts）中的神经元中，实现了刺激和包络信息的完全分离。
