Facilitatory mechanisms shape selectivity for the rate and direction of FM sweeps in the inferior colliculus of the pallid bat.
Facilitatory mechanisms shape selectivity for the rate and direction of FM sweeps in the inferior colliculus of the pallid bat.
复制标题
DOI：
10.1152/jn.00598.2009
复制
发表时间：
2010-07
影响因子：
2.5
通讯作者：
A. Williams;Z. Fuzessery
中科院分区：
文献类型：
--
作者：
A. Williams;Z. Fuzessery
苍白蝙蝠的下丘（IC）有很大比例的神经元选择性地对蝙蝠回声定位脉冲的速率和方向做出反应，向下FM扫描。先前已经描述了三种基本机制。在这里，我们描述了第四种机制，促进，形状扫描速率和方向的选择性。被研究的神经元被称为FM专家，因为它们对音调没有反应。大多数是选择性的向下扫描方向，这种偏好表示，即使在窄带，1 kHz的扫描，跨越只有一小部分的兴奋性感受野。这种选择性也表现在对两个延迟的音调的反应中，称为双音易化（TTF）。方向选择神经元表现出极大的促进反应时，较高频率的音调之前，较低频率的音调，模拟条件下扫。促进的时间不对称的程度准确预测方向选择性。当两个音调之间的频谱差异增加时，最佳延迟也会增加，并且可以用来预测神经元的首选扫描速率。为了确定TTF是否单独产生速率和方向选择性，从扫描中消除了也可以形成选择性的低频和高频抑制边带。在大多数情况下，选择性仍然存在。这些结果支持的想法，光谱延迟线，产生的重叠和总和的兴奋性输入只有当一个动态的刺激在一个方向上以特定的速度穿越一个感受野。
The inferior colliculus (IC) of the pallid bat has a large percentage of neurons that respond selectively to the rate and direction of the bat's echolocation pulse, a downward FM sweep. Three underlying mechanisms have been previously described. Here we describe a fourth mechanism, facilitation, that shapes selectivity for both sweep rate and direction. The neurons studied are termed FM specialists, because they do not respond to tones. Most were selective for the downward sweep direction, and this preference was expressed even when presented with narrowband, 1 kHz sweeps that crossed only a fraction of their excitatory receptive fields. This selectivity was also expressed in response to two tones delayed in time, termed two-tone facilitation (TTF). Direction-selective neurons showed a greatly facilitated response when a higher-frequency tone preceded a lower-frequency tone, simulating conditions in a downward sweep. The degree of temporal asymmetry in facilitation accurately predicted direction selectivity. When the spectral difference between the two tones was increased, the best delay also increased and could be used to predict a neuron's preferred sweep rate. To determine whether TTF alone created rate and direction selectivity, low- and high-frequency inhibitory sidebands, which can also shape selectivity, were eliminated from sweeps. In most cases, selectivity persisted. These results support the idea of spectral delay lines that produce an overlap and summation of excitatory inputs only when a dynamic stimulus traverses a receptive field in one direction at a specific velocity.