Wallace H Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia.
Joint PhD Program in Biomedical Engineering, Georgia Institute of Technology-Emory University-Peking University, Atlanta, Georgia.
J Neurophysiol. 2021 May 1;125(5):1833-1850. doi: 10.1152/jn.00261.2020. Epub 2021 Mar 24.
Sensory signals from the outside world are transduced at the periphery, passing through thalamus before reaching cortex, ultimately giving rise to the sensory representations that enable us to perceive the world. The thalamocortical circuit is particularly sensitive to the temporal precision of thalamic spiking due to highly convergent synaptic connectivity. Thalamic neurons can exhibit burst and tonic modes of firing that strongly influence timing within the thalamus. The impact of these changes in thalamic state on sensory encoding in the cortex, however, remains unclear. Here, we investigated the role of thalamic state on timing in the thalamocortical circuit of the vibrissa pathway in the anesthetized rat. We optogenetically hyperpolarized thalamus while recording single unit activity in both thalamus and cortex. Tonic spike-triggered analysis revealed temporally precise thalamic spiking that was locked to weak white-noise sensory stimuli, whereas thalamic burst spiking was associated with a loss in stimulus-locked temporal precision. These thalamic state-dependent changes propagated to cortex such that the cortical timing precision was diminished during the hyperpolarized (burst biased) thalamic state. Although still sensory driven, the cortical neurons became significantly less precisely locked to the weak white-noise stimulus. The results here suggests a state-dependent differential regulation of spike timing precision in the thalamus that could gate what signals are ultimately propagated to cortex. The majority of sensory signals are transmitted through the thalamus. There is growing evidence of complex thalamic gating through coordinated firing modes that have a strong impact on cortical sensory representations. Optogenetic hyperpolarization of thalamus pushed it into burst firing that disrupted precise time-locked sensory signaling, with a direct impact on the downstream cortical encoding, setting the stage for a timing-based thalamic gate of sensory signaling.
来自外界的感觉信号在外周被转换，通过丘脑到达皮层，最终产生使我们能够感知世界的感觉表象。丘脑-皮层回路对丘脑发放的时间精度特别敏感，因为其具有高度会聚的突触连接。丘脑神经元可以表现出爆发和持续放电模式，强烈影响丘脑内的时间。然而，这些丘脑状态变化对皮层感觉编码的影响尚不清楚。在这里，我们研究了在麻醉大鼠触须通路的丘脑-皮层回路中，丘脑状态对时间的作用。我们通过光遗传学使丘脑超极化，同时记录丘脑和皮层的单个神经元活动。持续发放的尖峰触发分析显示，时间精度很高的丘脑发放与弱白噪声感觉刺激锁定，而丘脑爆发发放与锁定时间精度的丧失相关。这些丘脑状态依赖性变化传播到皮层，使得在超极化（爆发偏向）丘脑状态下，皮层时间精度降低。尽管仍然是感觉驱动的，但皮层神经元对弱白噪声刺激的锁定精度显著降低。结果表明，在丘脑内存在状态依赖性的尖峰时间精度调节差异，这可能是对最终传播到皮层的信号进行门控的原因。大多数感觉信号通过丘脑传输。越来越多的证据表明，通过协调的发放模式进行复杂的丘脑门控，对皮层感觉表示有强烈影响。光遗传学使丘脑超极化，使其进入爆发发放模式，破坏了精确的时间锁定感觉信号，对下游皮层编码有直接影响，为基于时间的感觉信号丘脑门控奠定了基础。
