Department of Psychiatry, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Hum Brain Mapp. 2013 Jul;34(7):1568-78. doi: 10.1002/hbm.22011. Epub 2012 Feb 17.
The reduction of neural activity in response to repeated stimuli, repetition suppression, is one of the most robust experience-related cortical dynamics known to cognitive neuroscience. Functional magnetic resonance imaging (fMRI) studies during episodic memory encoding have demonstrated repetition suppression in the hippocampus and this reduction has been linked to successful memory formation. An emerging body of functional imaging evidence suggests that the posteromedial cortex, in addition to the medial temporal lobes, may have a pivotal role in successful episodic memory. This area typically deactivates during initial memory encoding, but its functional changes in response to repetitive encoding remain poorly specified. Here, we investigate the repetition-related changes in the posteromedial cortex as well as the hippocampus while the participants underwent an fMRI experiment involving repetitive encoding of face-name pairs. During the first encoding trial of face-name pairs, significant activation in the hippocampus was observed. The second and third encoding trials demonstrated a repetition suppression effect in the hippocampus, indicated by a stepwise decrease of activation. In contrast, the posteromedial cortex demonstrated significant deactivation during the initial encoding trial of face-name pairs. The second and third encoding trials demonstrated a stepwise decrease of deactivation, repetition enhancement, with activity at or above baseline levels in the final encoding trial. These findings demonstrate that hippocampus repetition suppression as well as posteromedial repetition enhancement is related to successful encoding processes and are discussed in relation to the default mode hypothesis as well as potential implications for understanding late-life amnestic disorders.
重复刺激引起的神经活动减少，即重复抑制，是认知神经科学中已知的最稳健的与经验相关的皮质动力学之一。在情景记忆编码期间进行的功能磁共振成像（fMRI）研究表明，海马体中存在重复抑制，这种抑制与成功的记忆形成有关。越来越多的功能成像证据表明，后内侧皮层除了内侧颞叶之外，可能在成功的情景记忆中具有关键作用。该区域通常在初始记忆编码期间失活，但对重复编码的功能变化仍未得到明确说明。在这里，我们研究了参与者进行涉及面孔-名字对重复编码的 fMRI 实验时，后内侧皮层与海马体的重复相关变化。在面孔-名字对的第一次编码试验中，观察到海马体的显著激活。第二和第三次编码试验显示出海马体的重复抑制效应，表现为激活逐渐减少。相比之下，在面孔-名字对的初始编码试验中，后内侧皮层表现出显著的去激活。第二和第三次编码试验显示出去激活的逐渐减少，重复增强，在最后一次编码试验中达到或超过基线水平的活动。这些发现表明，海马体的重复抑制和后内侧的重复增强与成功的编码过程有关，并与默认模式假说以及对理解老年遗忘障碍的潜在影响进行了讨论。
