Department of Psychology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
J Neurosci. 2012 Sep 19;32(38):12990-8. doi: 10.1523/JNEUROSCI.1892-12.2012.
Does the sustained, elevated neural activity observed during working memory tasks reflect the short-term retention of information? Functional magnetic resonance imaging (fMRI) data of delayed recognition of visual motion in human participants were analyzed with two methods: a general linear model (GLM) and multivoxel pattern analysis. Although the GLM identified sustained, elevated delay-period activity in superior and lateral frontal cortex and in intraparietal sulcus, pattern classifiers were unable to recover trial-specific stimulus information from these delay-active regions. The converse-no sustained, elevated delay-period activity but successful classification of trial-specific stimulus information-was true of posterior visual regions, including area MT+ (which contains both middle temporal area and medial superior temporal area) and calcarine and pericalcarine cortex. In contrast to stimulus information, pattern classifiers were able to extract trial-specific task instruction-related information from frontal and parietal areas showing elevated delay-period activity. Thus, the elevated delay-period activity that is measured with fMRI may reflect processes other than the storage, per se, of trial-specific stimulus information. It may be that the short-term storage of stimulus information is represented in patterns of (statistically) "subthreshold" activity distributed across regions of low-level sensory cortex that univariate methods cannot detect.
在工作记忆任务中观察到的持续升高的神经活动是否反映了信息的短期保留？使用两种方法分析了人类参与者视觉运动延迟识别的功能磁共振成像 (fMRI) 数据：一般线性模型 (GLM) 和多体素模式分析。虽然 GLM 确定了额侧和外侧额叶皮层以及顶内沟中的持续升高的延迟期活动，但模式分类器无法从这些延迟活动区域中恢复特定于试验的刺激信息。相反，后部视觉区域（包括包含中颞区和内侧上颞区的 MT+区以及距状回和旁距状回皮层）没有持续升高的延迟期活动，但可以成功分类特定于试验的刺激信息。与刺激信息不同，模式分类器能够从前额和顶叶区域提取与升高的延迟期活动相关的特定于试验的任务指令信息。因此，fMRI 测量的升高的延迟期活动可能反映了除特定于试验的刺激信息存储本身之外的过程。可能是刺激信息的短期存储是以分布在低水平感觉皮层区域中的（统计上）“亚阈值”活动模式表示的，而单变量方法无法检测到这些模式。
