Neurons in the temporal lobe cortex exhibit reduced responses when a stimulus or a stimulus feature is repeated. This phenomenon, termed “repetition suppression”, is the basis for many functional imaging studies that have used Blood Oxygenation Level Dependent (BOLD) activity differences between novel and repeated items as an index of neural selectivity in hippocampal subfields. However, it is not clear how hippocampal neural activity changes across repeated exposure to a stimulus. Here, we used direct intracranial electroencephalography (iEEG) recordings of hippocampal activity to examine whether neural activity in the human hippocampus is modulated across successive repetitions of an item. Time-frequency analyses revealed that high-frequency activity, which is thought to include gamma oscillations and possible correlates of multi-unit activity, declined monotonically across successive presentations of an item. In contrast, low-frequency oscillations in the alpha and beta bands monotonically increased across successive presentations of an object. These results provide support for the assumption that, at least under some circumstances, repetition suppression (as measured by declines in high-frequency activity) can be observed in the hippocampus, and these effects are accompanied by increases in low-frequency oscillations as well.

当重复刺激或刺激特征时，颞叶皮层中的神经元表现出降低的反应。这种现象被称为“重复抑制”，是许多功能成像研究的基础，该研究已使用新项目和重复项目之间的血氧依赖水平（BOLD）活性差异作为海马亚区神经选择性的指标。然而，尚不清楚在反复暴露于刺激下海马神经活动如何变化。在这里，我们使用海马活动的直接颅内脑电图（iEEG）记录来检查人类海马中的神经活动是否在项目的连续重复之间被调节。时频分析显示，高频活动被认为包括伽玛振荡和多单元活动的可能关联，在项目的连续展示中单调下降。相反，在对象的连续显示中，α和β波段的低频振荡单调增加。这些结果支持这样的假设：至少在某些情况下，在海马中可以观察到重复抑制（通过高频活动的下降来衡量），并且这些影响还伴随着低频振荡的增加。