Monkey prefrontal neurons during Sternberg task performance: full contents of working memory or most recent item?
Monkey prefrontal neurons during Sternberg task performance: full contents of working memory or most recent item?
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DOI：
10.1152/jn.00541.2016
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发表时间：
2017-06-01
影响因子：
2.5
通讯作者：
Olson, C. R.
中科院分区：
文献类型：
--
作者：
Konecky, R. O.;Smith, M. A.;Olson, C. R.
为了探索多项目工作记忆的大脑机制，我们监测了猕猴执行空间和色彩版本的斯滕贝格工作记忆任务时背外侧前额叶皮层神经元的活动。每次试验都需要在工作记忆中保存三个顺序呈现的样本，以便识别与其中一个相匹配的后续探针。猴子能够回忆起所有三个样本的水平远远高于机会，表现出适度的负荷和近因效应。前额叶神经元发出信号的身份，每个样品在延迟期间立即介绍。然而，随着每个新样本的出现，先前样本的代表性变得很弱，并转变为异常代码。一个线性分类器的基础上运行的人口活动在最后的延迟期间能够执行在大约的水平上的猴子的试验需要回忆的第三个样品，但表现出下降的性能试验需要回忆的第一个或第二个样品比观察到的猴子陡峭得多。我们的结论是，前额叶皮层的延迟期活动只代表最近的项目。除了前额延迟期的放电频率外，猴子们显然还将这种经典的工作记忆任务的表现建立在某种存储机制上。可能性包括前额叶皮层以外区域的延迟期活动和前额叶皮层内的变化，而这些变化并不表现在放电率的水平上。新&值得注意的是，长期以来人们一直认为，工作记忆中的项目是由背外侧前额叶皮层的延迟期活动编码的。在这里，我们描述了与这种观点相反的证据。在猴子执行一系列多项目工作记忆任务时，背外侧前额叶神经元几乎只编码最近呈现的样本的身份。关于早期样本的信息必须在前额叶皮层之外编码，或者在前额叶皮层内以一种神秘的代码表示。
To explore the brain mechanisms underlying multi-item working memory, we monitored the activity of neurons in the dorsolateral prefrontal cortex while macaque monkeys performed spatial and chromatic versions of a Sternberg working-memory task. Each trial required holding three sequentially presented samples in working memory so as to identify a subsequent probe matching one of them. The monkeys were able to recall all three samples at levels well above chance, exhibiting modest load and recency effects. Prefrontal neurons signaled the identity of each sample during the delay period immediately following its presentation. However, as each new sample was presented, the representation of antecedent samples became weak and shifted to an anomalous code. A linear classifier operating on the basis of population activity during the final delay period was able to perform at approximately the level of the monkeys on trials requiring recall of the third sample but showed a falloff in performance on trials requiring recall of the first or second sample much steeper than observed in the monkeys. We conclude that delay-period activity in the prefrontal cortex robustly represented only the most recent item. The monkeys apparently based performance of this classic working-memory task on some storage mechanism in addition to the prefrontal delay-period firing rate. Possibilities include delay-period activity in areas outside the prefrontal cortex and changes within the prefrontal cortex not manifest at the level of the firing rate.NEW & NOTEWORTHY It has long been thought that items held in working memory are encoded by delay-period activity in the dorsolateral prefrontal cortex. Here we describe evidence contrary to that view. In monkeys performing a serial multi-item working memory task, dorsolateral prefrontal neurons encode almost exclusively the identity of the sample presented most recently. Information about earlier samples must be encoded outside the prefrontal cortex or represented within the prefrontal cortex in a cryptic code.