Abstract：
Auditory neural networks in the brain naturally entrain to rhythmic stimuli. Such synchronization is an accessible index of local network performance as captured by EEG. Across species, click trains delivered ∼ 40 Hz show strong entrainment with primary auditory cortex (Actx) being a principal source. Imaging studies have revealed additional cortical sources, but it is unclear if they are functionally distinct. Since auditory processing evolves hierarchically, we hypothesized that local synchrony would differ between between primary and association cortices. In female SD rats (N = 12), we recorded 40 Hz click train-elicited gamma oscillations using epidural electrodes situated at two distinct sites; one above the prefrontal cortex (PFC) and another above the Actx, after dosing with saline (1 ml/kg, sc) or the NMDA antagonist, MK801 (0.025, 0.05 or 0.1 mpk), in a blocked crossover design. Post-saline, both regions showed a strong 40 Hz auditory steady state response (ASSR). The latencies for the N1 response were ∼ 16 ms (Actx) and ∼ 34 ms (PFC). Narrow band (38-42 Hz) gamma oscillations appeared rapidly (<40 ms from stim onset at Actx but in a more delayed fashion (∼200 ms) at PFC. MK801 augmented gamma synchrony at Actx while dose-dependently disrupting at the PFC. Event-related gamma (but not beta) coherence, an index of long-distance connectivity, was disrupted by MK801. In conclusion, local network gamma synchrony in a higher order association cortex performs differently from that of the primary auditory cortex. We discuss these findings in the context of evolving sound processing across the cortical hierarchy.
摘要：
大脑中的听觉神经网络自然地夹带有节奏的刺激。这种同步是由EEG捕获的本地网络性能的可访问指标。跨物种，点击列车交付~40赫兹显示出强烈的夹带，初级听觉皮层(Actx)是主要来源。影像学研究揭示了额外的皮质来源，但目前尚不清楚它们在功能上是否不同。由于听觉处理是分层发展的，我们假设局部同步性在主皮层和关联皮层之间会有所不同。在雌性SD大鼠（N=12）中，我们使用位于两个不同部位的硬膜外电极记录了40Hz的点击训练引起的伽马振荡；一个在前额叶皮层（PFC）上方，另一个在Actx上方，用生理盐水（1毫升/千克，sc)或NMDA拮抗剂，MK801(0.025,0.05或0.1mpk),在一个封闭的交叉设计。盐水后，这两个区域都显示出强的40Hz听觉稳态反应（ASSR）。N1响应的延迟为~16ms(Actx)和~34ms(PFC)。窄带（38-42Hz）伽马振荡迅速出现（从Actx的刺激开始<40ms，但在PFC以更延迟的方式（〜200ms）出现。MK801增强了Actx上的γ同步性，同时在PFC上剂量依赖性地破坏。事件相关的伽马(而不是β)相干性，长距离连通性指数，被MK801打断了.总之,更高阶关联皮层中的本地网络伽马同步与初级听觉皮层的表现不同。我们在皮层层次结构中不断发展的声音处理的背景下讨论这些发现。
