Severo Frederico, Valente Mafalda, Shemesh Noam
Champalimaud Research, Champalimaud Foundation, Lisbon, Portugal.
Imaging Neurosci (Camb). 2025 Sep 22;3. doi: 10.1162/IMAG.a.155. eCollection 2025.
The role of subcortical structures in binaural integration is of great interest for auditory processing. The inferior colliculus (IC) is the main auditory midbrain center where ascending and descending auditory projections converge, which was suggested to encode auditory information via a push-pull mechanism (a coordinated antagonistic neural mechanism for adaptive response control) between the two ICs. However, the origin of this push-pull mechanism in the brain and how it interacts with other upstream/downstream subcortical areas are still a matter of great debate. Here, we harness functional MRI (fMRI) in combination with IC lesions in the rat to dissect the push-pull interaction from a pathway-wide perspective. We find evidence for the push-pull mechanism in IC through opposing negative/positive fMRI signals in the ipsilateral/contralateral ICs upon monaural stimulation. By unilaterally lesioning the corresponding contralateral IC, we demonstrate the necessity of collicular integrity and intercollicular interactions for the push-pull interaction. Using binaural stimulation and IC lesions, we show that the push-pull interaction is exerted also in binaural processing. Finally, we demonstrate that, at least at the population level revealed by fMRI, the main push-pull interactions occur first at the IC level, and not earlier, and that the outcome of the push-pull "calculation" is relayed downstream to the medial geniculate body (MGB). This dissection of the push-pull interaction sheds light into subcortical auditory function.
皮层下结构在双耳整合中的作用对于听觉处理具有极大的研究价值。下丘（IC）是主要的听觉中脑中心，上行和下行听觉投射在此汇聚，有人提出它通过两个下丘之间的推挽机制（一种用于适应性反应控制的协调拮抗神经机制）对听觉信息进行编码。然而，这种推挽机制在大脑中的起源以及它如何与其他上游/下游皮层下区域相互作用，仍然是一个备受争议的问题。在此，我们利用功能磁共振成像（fMRI）结合大鼠的下丘损伤，从全通路的角度剖析推挽相互作用。我们发现，在单耳刺激时，同侧/对侧下丘中相反的负/正fMRI信号为下丘中的推挽机制提供了证据。通过单侧损伤相应的对侧下丘，我们证明了下丘完整性和下丘间相互作用对于推挽相互作用的必要性。利用双耳刺激和下丘损伤，我们表明推挽相互作用也在双耳处理中发挥作用。最后，我们证明，至少在fMRI揭示的群体水平上，主要的推挽相互作用首先发生在下丘水平，而非更早，并且推挽“计算”的结果会向下传递至内侧膝状体（MGB）。对推挽相互作用的这一剖析为皮层下听觉功能提供了新的见解。
