Tan A Y Y, Atencio C A, Polley D B, Merzenich M M, Schreiner C E
Coleman Memorial Laboratory and W.M. Keck Foundation Center for Integrative Neuroscience, University of California, San Francisco, 513 Parnassus Avenue, HSE-844, San Francisco, CA 94143-0444, USA.
Neuroscience. 2007 Apr 25;146(1):449-62. doi: 10.1016/j.neuroscience.2007.01.019. Epub 2007 Feb 22.
Intensity-tuned auditory cortex neurons have spike rates that are nonmonotonic functions of sound intensity: their spike rate initially increases and peaks as sound intensity is increased, then decreases as sound intensity is further increased. They are either "unbalanced," receiving disproportionally large synaptic inhibition at high sound intensities; or "balanced," receiving intensity-tuned synaptic excitation and identically tuned synaptic inhibition which neither creates enhances nor creates intensity-tuning. It has remained unknown if the synaptic inhibition received by unbalanced neurons enhances intensity-tuning already present in the synaptic excitation, or if it creates intensity-tuning that is not present in the synaptic excitation. Here we show, using in vivo whole cell recordings in pentobarbital-anesthetized rats, that in some unbalanced intensity-tuned auditory cortex neurons synaptic inhibition enhances the intensity-tuning; while in others it actually creates the intensity-tuning. The lack of balance between synaptic excitation and inhibition was not always apparent in their peak amplitudes, but could sometimes be revealed only by considering their relative timing. Since synaptic inhibition is essentially cortical in origin, the unbalanced neurons in which inhibition creates intensity-tuning provide examples of auditory feature-selectivity arising de novo at the auditory cortex.
随着声音强度增加，它们的放电率最初升高并达到峰值，然后随着声音强度进一步增加而降低。它们要么是“不平衡的”，即在高声强时接受不成比例的大突触抑制；要么是“平衡的”，接受强度调谐的突触兴奋和相同调谐的突触抑制，这既不会增强也不会产生强度调谐。尚不清楚不平衡神经元接受的突触抑制是增强了突触兴奋中已存在的强度调谐，还是产生了突触兴奋中不存在的强度调谐。在这里，我们使用戊巴比妥麻醉大鼠的体内全细胞记录表明，在一些不平衡的强度调谐听觉皮层神经元中，突触抑制增强了强度调谐；而在另一些神经元中，它实际上产生了强度调谐。突触兴奋和抑制之间缺乏平衡在它们的峰值幅度中并不总是明显的，但有时只有通过考虑它们的相对时间才能揭示出来。由于突触抑制本质上起源于皮层，抑制产生强度调谐的不平衡神经元提供了听觉皮层从头产生听觉特征选择性的例子。
