Xiong Colin, Liu Xiuping, Kong Lingzhi, Yan Jun
Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
PLoS One. 2020 Jul 29;15(7):e0236760. doi: 10.1371/journal.pone.0236760. eCollection 2020.
The neural mechanisms underlying forward suppression in the auditory cortex remain a puzzle. Little attention is paid to thalamic contribution despite the important fact that the thalamus gates upstreaming information to the auditory cortex. This study compared the time courses of forward suppression in the auditory thalamus, thalamocortical inputs and cortex using the two-tone stimulus paradigm. The preceding and succeeding tones were 20-ms long. Their frequency and amplitude were set at the characteristic frequency and 20 dB above the minimum threshold of given neurons, respectively. In the ventral division of the medial geniculate body of the thalamus, we found that the duration of complete forward suppression was about 75 ms and the duration of partial suppression was from 75 ms to about 300 ms after the onset of the preceding tone. We also found that during the partial suppression period, the responses to the succeeding tone were further suppressed in the primary auditory cortex. The forward suppression of thalamocortical field excitatory postsynaptic potentials was between those of thalamic and cortical neurons but much closer to that of thalamic ones. Our results indicate that early suppression in the cortex could result from complete suppression in the thalamus whereas later suppression may involve thalamocortical and intracortical circuitry. This suggests that the complete suppression that occurs in the thalamus provides the cortex with a "silence" window that could potentially benefit cortical processing and/or perception of the information carried by the preceding sound.
听觉皮层中前向抑制的神经机制仍是一个谜。尽管丘脑将上游信息传递至听觉皮层这一重要事实，但丘脑的作用却很少受到关注。本研究使用双音刺激范式比较了听觉丘脑、丘脑皮质输入和皮层中前向抑制的时间进程。前导音和后续音时长均为20毫秒。它们的频率和幅度分别设置为特征频率以及比给定神经元的最小阈值高20分贝。在丘脑内侧膝状体的腹侧部分，我们发现完全前向抑制的持续时间约为75毫秒，部分抑制的持续时间在前导音开始后为75毫秒至约300毫秒。我们还发现，在部分抑制期间，初级听觉皮层中对后续音的反应会进一步受到抑制。丘脑皮质场兴奋性突触后电位的前向抑制介于丘脑神经元和皮层神经元之间，但更接近丘脑神经元。我们的结果表明，皮层中的早期抑制可能源于丘脑中的完全抑制，而后期抑制可能涉及丘脑皮质和皮质内环路。这表明丘脑中发生的完全抑制为皮层提供了一个“沉默”窗口，这可能有利于皮层对前导声音携带的信息进行处理和/或感知。
