Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98115, USA.
J Neurosci. 2013 Apr 10;33(15):6310-20. doi: 10.1523/JNEUROSCI.4964-12.2013.
Signals throughout the nervous system diverge into parallel excitatory and inhibitory pathways that later converge on downstream neurons to control their spike output. Converging excitatory and inhibitory synaptic inputs can exhibit a variety of temporal relationships. A common motif is feedforward inhibition, in which an increase (decrease) in excitatory input precedes a corresponding increase (decrease) in inhibitory input. The delay of inhibitory input relative to excitatory input originates from an extra synapse in the circuit shaping inhibitory input. Another common motif is push-pull or "crossover" inhibition, in which increases (decreases) in excitatory input occur together with decreases (increases) in inhibitory input. Primate On midget ganglion cells receive primarily feedforward inhibition and On parasol cells receive primarily crossover inhibition; this difference provides an opportunity to study how each motif shapes the light responses of cell types that play a key role in visual perception. For full-field stimuli, feedforward inhibition abbreviated and attenuated responses of On midget cells, while crossover inhibition, though plentiful, had surprisingly little impact on the responses of On parasol cells. Spatially structured stimuli, however, could cause excitatory and inhibitory inputs to On parasol cells to increase together, adopting a temporal relation very much like that for feedforward inhibition. In this case, inhibitory inputs substantially abbreviated a cell's spike output. Thus inhibitory input shapes the temporal stimulus selectivity of both midget and parasol ganglion cells, but its impact on responses of parasol cells depends strongly on the spatial structure of the light inputs.
神经系统中的信号会发散为平行的兴奋和抑制通路，然后在下游神经元上汇聚，以控制它们的脉冲输出。汇聚的兴奋和抑制性突触输入可以表现出多种时间关系。一个常见的模式是前馈抑制，其中兴奋输入的增加（减少）先于相应的抑制输入的增加（减少）。抑制性输入相对于兴奋输入的延迟源于电路中形成抑制性输入的额外突触。另一个常见的模式是推挽或“交叉”抑制，其中兴奋输入的增加（减少）与抑制输入的减少（增加）同时发生。灵长类动物的小神经节细胞主要接收前馈抑制，而伞形神经节细胞主要接收交叉抑制；这种差异为研究每种模式如何塑造在视觉感知中发挥关键作用的细胞类型的光反应提供了机会。对于全场刺激，前馈抑制缩短并减弱了 On 小细胞的反应，而尽管交叉抑制丰富，但对 On 伞形细胞的反应几乎没有影响。然而，空间结构的刺激可以使 On 伞形细胞的兴奋和抑制输入同时增加，采用与前馈抑制非常相似的时间关系。在这种情况下，抑制性输入大大缩短了细胞的脉冲输出。因此，抑制性输入塑造了小神经节和伞形神经节细胞的时间刺激选择性，但它对伞形细胞反应的影响强烈依赖于光输入的空间结构。
