Université Pierre et Marie Curie (Paris6), LENA CNRS UPR640, Paris, France.
J Cogn Neurosci. 2009 Dec;21(12):2287-99. doi: 10.1162/jocn.2008.21155.
Oscillatory synchrony in the gamma band (30-120 Hz) has been involved in various cognitive functions including conscious perception and learning. Explicit memory encoding, in particular, relies on enhanced gamma oscillations. Does this finding extend to unconscious memory encoding? Can we dissociate gamma oscillations related to unconscious learning and to conscious perception? We investigate these issues in a magnetoencephalographic experiment using a modified version of the contextual cueing paradigm. In this visual search task, repeated presentation of search arrays triggers an unconscious spatial learning process that speeds reaction times but leaves conscious perception unaffected. In addition to a high-frequency perceptual gamma activity present throughout the experiment, we reveal the existence of a fronto-occipital network synchronized in the low gamma range specifically engaged in unconscious learning. This network shows up as soon as a display is searched for the second time and disappears as behavior gets affected. We suggest that oscillations in this network shape neural processing to build an efficient neural route for learned displays. Accordingly, in the last part of the experiment, evoked responses dissociate learned images at early latencies, suggesting that a sharpened representation is activated without resort on learning gamma oscillations, whereas perceptual gamma oscillations remain unaffected.
γ 频段（30-120 Hz）的振荡同步已涉及到各种认知功能，包括意识知觉和学习。特别是外显记忆编码依赖于增强的γ 振荡。这一发现是否适用于无意识的记忆编码？我们能否区分与无意识学习和意识知觉相关的γ 振荡？我们使用上下文线索范式的修改版本在脑磁图实验中研究了这些问题。在这个视觉搜索任务中，重复呈现搜索数组会引发无意识的空间学习过程，从而加快反应时间，但不会影响意识知觉。除了在整个实验中存在的高频感知γ 活动外，我们还揭示了一个特定的额枕网络的存在，该网络在低频γ 范围内同步，专门参与无意识学习。这个网络一旦第二次搜索显示就会出现，并且随着行为的变化而消失。我们认为，该网络中的振荡可以塑造神经处理过程，为学习过的显示建立有效的神经途径。因此，在实验的最后一部分，诱发反应在早期潜伏期区分了学习过的图像，这表明激活了更敏锐的表示，而无需依赖学习的γ 振荡，而感知γ 振荡则不受影响。
