Qian Longlong, Jia Chongchong, Wang Jiangtao, Shi Li, Wang Zhizhong, Wang Songwei
Zhengzhou University, Zhengzhou, China.
Henan Provincial Key Laboratory of Brain Science and Brain-Computer Interface, Zhengzhou University, Zhengzhou, China.
Sci Rep. 2025 May 25;15(1):18260. doi: 10.1038/s41598-025-02255-w.
The nucleus isthmi pars magnocellularis (Imc) serves as a critical node in the avian midbrain network for encoding stimulus salience and selection. While reciprocal inhibitory projections among Imc neurons (inhibitory loop) are known to govern stimulus selection, existing studies have predominantly focused on stimulus selection under stimuli of constant relative intensity. However, animals typically encounter complex and changeable visual scenes. Thus, how Imc neurons represent stimulus selection under varying relative stimulus intensities remains unclear. Here, we examined the dynamics of stimulus selection by in vivo recording of Imc neurons' responses to spatiotemporally successive visual stimuli divided into two segments: the previous stimulus and the post stimulus. Our data demonstrate that Imc neurons can encode sensory memory of the previous stimulus, which modulates competition and salience representation in the post stimulus. This history-dependent modulation is also manifested in persistent neural activity after stimulus cessation. We identified, through neural tracing, focal inactivation, and computational modeling experiments, projections from the nucleus isthmi pars parvocellularis (Ipc) to "shepherd's crook" (Shc) neurons, which could be either direct or indirect. These projections enhance Imc neurons' responses and persistent neural activity after stimulus cessation. This connectivity supports a Shc-Ipc-Shc excitatory loop in the midbrain network. The coexistence of excitatory and inhibitory loops provides a neural substrate for continuous attractor network models, a proposed framework for neural information representation. This study also offers a potential explanation for how animals maintain short-term attention to targets in complex and changeable environments.
峡核大细胞部（Imc）是鸟类中脑网络中用于编码刺激显著性和选择的关键节点。虽然已知Imc神经元之间的相互抑制性投射（抑制性回路）控制刺激选择，但现有研究主要集中在恒定相对强度刺激下的刺激选择。然而，动物通常会遇到复杂多变的视觉场景。因此，Imc神经元在不同相对刺激强度下如何表征刺激选择仍不清楚。在这里，我们通过体内记录Imc神经元对时空连续视觉刺激（分为两个部分：前一个刺激和后一个刺激）的反应，研究了刺激选择的动态过程。我们的数据表明，Imc神经元可以编码前一个刺激的感觉记忆，这会调节后一个刺激中的竞争和显著性表征。这种依赖历史的调节也体现在刺激停止后的持续神经活动中。我们通过神经追踪、局灶性失活和计算建模实验，确定了从峡核小细胞部（Ipc）到“牧羊钩”（Shc）神经元的投射，这些投射可以是直接的，也可以是间接的。这些投射增强了Imc神经元的反应以及刺激停止后的持续神经活动。这种连接性支持了中脑网络中的Shc-Ipc-Shc兴奋性回路。兴奋性和抑制性回路的共存为连续吸引子网络模型（一种提出的神经信息表征框架）提供了神经基础。这项研究还为动物如何在复杂多变的环境中维持对目标的短期注意力提供了一个潜在的解释。
