Mease Rebecca A, Sumser Anton, Sakmann Bert, Groh Alexander
Institute for Neuroscience of the Technische Universität München, 80802 Munich, Germany Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, 81675 Munich, Germany.
Institute for Neuroscience of the Technische Universität München, 80802 Munich, Germany.
Cereb Cortex. 2016 Aug;26(8):3461-75. doi: 10.1093/cercor/bhw123. Epub 2016 May 12.
The cortex connects to the thalamus via extensive corticothalamic (CT) pathways, but their function in vivo is not well understood. We investigated "top-down" signaling from cortex to thalamus via the cortical layer 5B (L5B) to posterior medial nucleus (POm) pathway in the whisker system of the anesthetized mouse. While L5B CT inputs to POm are extremely strong in vitro, ongoing activity of L5 neurons in vivo might tonically depress these inputs and thereby block CT spike transfer. We find robust transfer of spikes from the cortex to the thalamus, mediated by few L5B-POm synapses. However, the gain of this pathway is not constant but instead is controlled by global cortical Up and Down states. We characterized in vivo CT spike transfer by analyzing unitary PSPs and found that a minority of PSPs drove POm spikes when CT gain peaked at the beginning of Up states. CT gain declined sharply during Up states due to frequency-dependent adaptation, resulting in periodic high gain-low gain oscillations. We estimate that POm neurons receive few (2-3) active L5B inputs. Thus, the L5B-POm pathway strongly amplifies the output of a few L5B neurons and locks thalamic POm sub-and suprathreshold activity to cortical L5B spiking.
皮层通过广泛的皮质丘脑（CT）通路与丘脑相连，但其在体内的功能尚未得到充分了解。我们在麻醉小鼠的触须系统中，研究了从皮层经第5B层（L5B）到后内侧核（POm）通路的“自上而下”信号传递。虽然在体外，L5B向POm的CT输入非常强，但L5神经元在体内的持续活动可能会持续抑制这些输入，从而阻断CT峰电位传递。我们发现，少数L5B-POm突触介导了从皮层到丘脑的峰电位的稳健传递。然而，该通路的增益并非恒定不变，而是受全局皮层上行和下行状态的控制。我们通过分析单突触后电位（PSP）来表征体内CT峰电位传递，发现当CT增益在上升状态开始时达到峰值时，少数PSP驱动了POm峰电位。由于频率依赖性适应，CT增益在上升状态期间急剧下降，导致周期性的高增益-低增益振荡。我们估计POm神经元仅接收少量（2-3个）活跃的L5B输入。因此，L5B-POm通路强烈放大了少数L5B神经元的输出，并将丘脑POm的阈下和阈上活动锁定为与皮层L5B的峰电位同步。
