Eldreth Dana A, Patterson Michael D, Porcelli Anthony J, Biswal Bharat B, Rebbechi Donovan, Rypma Bart
Department of Psychology, Rutgers University, Smith Hall, 101 Warren Street, Newark, NJ 07102, USA.
Brain Res. 2006 Dec 6;1123(1):145-56. doi: 10.1016/j.brainres.2006.07.129. Epub 2006 Oct 30.
The prefrontal cortex (PFC) is known to subserve working memory (WM) processes. Brain imaging studies of WM using delayed response tasks (DRTs) have shown memory-load-dependent activation increases in dorsal prefrontal cortex (PFC) regions. These activation increases are believed to reflect manipulation of to-be-remembered information in the service of memory-consolidation. This speculation has been based on observations of similar activation increases in tasks that overtly require manipulation by instructing participants to reorder to-be-remembered list items. In this study, we tested the assumption of functional equivalence between these two types of WM tasks. Participants performed a DRT under two conditions with memory loads ranging from 3 to 6 letters. In an "item-order" condition, participants were required to remember letters in the order in which they were presented. In a "reordering" condition, participants were required to remember the letters in alphabetical order. Load-related activation increases were observed during the encoding and maintenance periods of the order maintenance condition, whereas load-related activation decreases were observed in the same periods of the reordering condition. These results suggest that (1) the neural substrates associated with long-list retention and those associated with reordering are not equivalent, (2) cognitive processes associated with long-list retention may be more closely approximated by item-order maintenance than by reordering, and (3) multiple forms of WM manipulation are dissociable on the basis of fMRI data.
前额叶皮质（PFC）已知对工作记忆（WM）过程起作用。使用延迟反应任务（DRT）对WM进行的脑成像研究表明，背侧前额叶皮质（PFC）区域的激活增加与记忆负荷相关。这些激活增加被认为反映了为巩固记忆而对要记忆的信息进行的操作。这种推测基于在明确要求参与者对要记忆的列表项目进行重新排序的任务中观察到的类似激活增加。在本研究中，我们测试了这两种类型的WM任务之间功能等效性的假设。参与者在两种条件下执行DRT，记忆负荷范围为3至6个字母。在“项目顺序”条件下，参与者被要求按呈现的顺序记住字母。在“重新排序”条件下，参与者被要求按字母顺序记住字母。在顺序维持条件的编码和维持期观察到与负荷相关的激活增加，而在重新排序条件的同一时期观察到与负荷相关的激活减少。这些结果表明：（1）与长列表保留相关的神经基质和与重新排序相关的神经基质不等同；（2）与长列表保留相关的认知过程可能通过项目顺序维持比通过重新排序更接近；（3）基于功能磁共振成像（fMRI）数据，多种形式的WM操作是可分离的。
