The startle reflex, which interferes with on-going cognitive/behavioral activities, is of important protective function for humans and animals. Prepulse inhibition (PPI), as an operational measure of sensorimotor gating, is the suppression of the startle reflex in response to an intense startling stimulus (pulse) when this startling stimulus is shortly preceded by a weaker non-startling stimulus (prepulse). In both humans and laboratory animals, PPI can be enhanced by facilitating selective attention to the prepulse, suggesting that higher-order cognitive/perceptual processes modulate PPI. It has been well known that both the cholinergic system located in the basal forebrain and the deep layers of the superior colliculus in the PPI-mediating circuit are top-down modulated by the medial agranular cortex (AGm), which is a subdivision of the medial prefrontal cortex (PFC) and has wide axonal connections with both cortical regions (including the posterior parietal cortex) and subcortical structures critical for attention/orientation processes. This study investigated whether the AGm is involved in attentional modulation of PPI. The results showed that PPI was enhanced by fear conditioning of the prepulse, and then further enhanced by perceived spatial separation between the conditioned prepulse and a back-ground masking noise based on the auditory precedence effect. Bilateral injection of 2-mM kynurenic acid, a broad spectrum antagonist of glutamate receptors, into the AGm, but not the primary somatosensory cortex, eliminated these two types of attentional enhancement of PPI. Thus, the AGm plays a role in facilitating attention to the prepulse and is involved in the top-down modulation of PPI.

中文翻译：

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内侧颗粒状皮质介导注意力增强惊吓反射的前脉冲抑制。

惊吓反射会干扰正在进行的认知/行为活动，对人类和动物具有重要的保护作用。前脉冲抑制（PPI）作为感觉运动门控的一种操作措施，是在强烈的惊吓刺激（脉冲）后不久，较弱的非惊吓刺激（预脉冲）后，对惊吓反射的抑制。在人类和实验动物中，可以通过促进对前搏的选择性注意来增强PPI，这表明较高阶的认知/感知过程可调节PPI。众所周知，位于基底前脑的胆碱能系统和PPI介导回路中上丘的深层均由内侧颗粒状皮质（AGm）自上而下调节，它是内侧前额叶皮层（PFC）的一个子部分，并且与皮质区域（包括后顶叶皮质）和对注意力/定向过程至关重要的皮质下结构都有广泛的轴突连接。这项研究调查了AGm是否参与PPI的注意力调节。结果表明，通过对预脉冲的恐惧调节增强了PPI，然后根据听觉优先效应，通过调节的预脉冲与背景掩蔽噪声之间的空间分隔进一步提高了PPI。向AGm中双向注射2-mM尿酸（一种广谱的谷氨酸受体拮抗剂），而不是向最初的体感皮层注射，消除了这两种类型的PPI注意力增强。从而，