Center for Neuroscience and Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, California 95618, USA.
J Neurosci. 2012 Jul 4;32(27):9323-34. doi: 10.1523/JNEUROSCI.5832-11.2012.
The effect of attention on single neuron responses in the auditory system is unresolved. We found that when monkeys discriminated temporally amplitude modulated (AM) from unmodulated sounds, primary auditory cortical (A1) neurons better discriminated those sounds than when the monkeys were not discriminating them. This was observed for both average firing rate and vector strength (VS), a measure of how well neurons temporally follow the stimulus' temporal modulation. When data were separated by nonsynchronized and synchronized responses, the firing rate of nonsynchronized responses best distinguished AM- noise from unmodulated noise, followed by VS for synchronized responses, with firing rate for synchronized neurons providing the poorest AM discrimination. Firing rate-based AM discrimination for synchronized neurons, however, improved most with task engagement, showing that the least sensitive code in the passive condition improves the most with task engagement. Rate coding improved due to larger increases in absolute firing rate at higher modulation depths than for lower depths and unmodulated sounds. Relative to spontaneous activity (which increased with engagement), the response to unmodulated sounds decreased substantially. The temporal coding improvement--responses more precisely temporally following a stimulus when animals were required to attend to it--expands the framework of possible mechanisms of attention to include increasing temporal precision of stimulus following. These findings provide a crucial step to understanding the coding of temporal modulation and support a model in which rate and temporal coding work in parallel, permitting a multiplexed code for temporal modulation, and for a complementary representation of rate and temporal coding.
听觉系统中单神经元对注意力的反应的影响尚未解决。我们发现，当猴子区分具有时间幅度调制（AM）的声音与未调制的声音时，初级听觉皮层（A1）神经元比不进行区分时更好地区分这些声音。这一点在平均发放率和向量强度（VS）上都得到了观察，后者是衡量神经元对刺激的时间调制跟随程度的指标。当数据根据非同步和同步响应进行分离时，非同步响应的发放率最好地区分 AM-噪声与未调制噪声，其次是同步响应的 VS，而同步神经元的发放率提供的 AM 区分最差。然而，同步神经元的基于发放率的 AM 区分随着任务参与度的提高而得到最大改善，表明在被动条件下最不敏感的代码随着任务参与度的提高而得到最大改善。由于在更高调制深度下绝对发放率的增加比在较低深度和未调制声音下更大，因此基于速率的 AM 区分得到了改善。与自发活动（随参与度增加而增加）相比，对未调制声音的反应大大减少。随着动物需要注意到它，时间编码的改善——对刺激的响应在时间上更加精确——扩展了注意力可能机制的框架，包括增加对刺激的时间精度跟随。这些发现为理解时间调制的编码提供了重要的一步，并支持一种模型，即速率和时间编码并行工作，允许对时间调制进行复用编码，并对速率和时间编码进行互补表示。
