Macias Silvio, Bakshi Kushal, Garcia-Rosales Francisco, Hechavarria Julio C, Smotherman Michael
Department of Biology, Texas A&M University, College Station, Texas, United States of America.
Institut für Zellbiologie und Neurowissenschaft, Goethe-Universität, Frankfurt/M., Germany.
PLoS Biol. 2020 Nov 10;18(11):e3000831. doi: 10.1371/journal.pbio.3000831. eCollection 2020 Nov.
Echolocating bats rely upon spectral interference patterns in echoes to reconstruct fine details of a reflecting object's shape. However, the acoustic modulations required to do this are extremely brief, raising questions about how their auditory cortex encodes and processes such rapid and fine spectrotemporal details. Here, we tested the hypothesis that biosonar target shape representation in the primary auditory cortex (A1) is more reliably encoded by changes in spike timing (latency) than spike rates and that latency is sufficiently precise to support a synchronization-based ensemble representation of this critical auditory object feature space. To test this, we measured how the spatiotemporal activation patterns of A1 changed when naturalistic spectral notches were inserted into echo mimic stimuli. Neurons tuned to notch frequencies were predicted to exhibit longer latencies and lower mean firing rates due to lower signal amplitudes at their preferred frequencies, and both were found to occur. Comparative analyses confirmed that significantly more information was recoverable from changes in spike times relative to concurrent changes in spike rates. With this data, we reconstructed spatiotemporal activation maps of A1 and estimated the level of emerging neuronal spike synchrony between cortical neurons tuned to different frequencies. The results support existing computational models, indicating that spectral interference patterns may be efficiently encoded by a cascading tonotopic sequence of neural synchronization patterns within an ensemble of network activity that relates to the physical features of the reflecting object surface.
利用回声定位的蝙蝠依靠回声中的频谱干涉图样来重建反射物体形状的精细细节。然而，做到这一点所需的声学调制极为短暂，这就引发了关于它们的听觉皮层如何编码和处理如此快速且精细的频谱时间细节的问题。在此，我们检验了这样一个假设：初级听觉皮层（A1）中生物声纳目标形状的表征通过 spike 时间（潜伏期）的变化比 spike 率更可靠地编码，并且潜伏期足够精确，以支持基于同步的这一关键听觉对象特征空间的整体表征。为了验证这一点，我们测量了在回声模拟刺激中插入自然频谱缺口时 A1 的时空激活模式是如何变化的。由于在其偏好频率处信号幅度较低，预计调谐到缺口频率的神经元会表现出更长的潜伏期和更低的平均放电率，而这两点都被发现确实如此。比较分析证实，相对于 spike 率的同时变化，从 spike 时间的变化中可恢复的信息要多得多。利用这些数据，我们重建了 A1 的时空激活图，并估计了调谐到不同频率的皮层神经元之间出现的神经元 spike 同步水平。结果支持了现有的计算模型，表明频谱干涉图样可能通过与反射物体表面物理特征相关的网络活动整体中的级联音调序列神经同步模式被有效地编码。
