Postle B R, Berger J S, Taich A M, D'Esposito M
Department of Psychology, University of Wisconsin, Madison, 53706-1696, USA.
J Cogn Neurosci. 2000;12 Suppl 2:2-14. doi: 10.1162/089892900564028.
We examined, with event-related fMRI, two hypotheses about the organization of human working memory function in frontal cortex: (1) that a region immediately anterior to the frontal eye fields (FEF) (superior frontal cortex, SFC) is specialized for spatial working memory (Courtney, et al., 1998); and (2) that dorsolateral prefrontal cortex (PFC) plays a privileged role in the manipulation of spatial stimuli held in working memory (Owen, et al., 1996; Petrides 1994). Our delayed-response task featured 2-D arrays of irregularly arranged squares that were highlighted serially in a random sequence. The Forward Memory condition required maintenance of the spatio-temporal sequence, the Manipulate Memory condition required reordering this sequence into a new spatially defined order, the Guided Saccade condition required saccades to highlighted squares in the array, but no memory, and the Free Saccade condition required self-paced, horizontal saccades. The comparison of fMRI signal intensity associated with 2-D saccade generation (Guided Saccades) versus fMRI signal intensity associated with the delay period of the working memorials condition revealed no evidence for greater working memory-related activity than saccade-related activity in SFC in any individual subject, nor at the level of the group, and greater 2-D saccade than delay-period activity in three of five subjects. These results fail to support the hypothesis that spatial working memory-related activity is represented preferentially in a region of SFC anterior to the FEF (Courtney, et al., 1998). The comparison of maintenance versus manipulation of spatio-temporal information in working memory revealed significantly greater activity associated with the latter in dorsolateral PFC, but not in ventrolateral PFC or in SFC. These results suggest that the delay-related function of SFC is limited to the maintenance of spatial information, and that this region does not support the nonmnemonic executive control functions supported by dorsolateral PFC. These results also indicate that the preferential recruitment of dorsolateral PFC for the manipulation of information held in working memory applies to tasks employing spatial stimuli, as well as to tasks employing verbal stimuli (D'Esposito, et al., 1999); Petrides et al., 1993; Postle et al., 1999).
我们利用事件相关功能磁共振成像技术，检验了关于额叶皮质中人类工作记忆功能组织的两种假说：（1）额叶眼区（FEF）前方紧邻的一个区域（额上皮质，SFC）专门负责空间工作记忆（考特尼等人，1998年）；（2）背外侧前额叶皮质（PFC）在对工作记忆中保存的空间刺激进行操作时起特殊作用（欧文等人，1996年；彼得里德斯，1994年）。我们的延迟反应任务以不规则排列的正方形二维阵列呈现，这些正方形以随机顺序依次高亮显示。前向记忆条件要求维持时空序列，操作记忆条件要求将该序列重新排列成新的空间定义顺序，引导扫视条件要求扫视阵列中高亮显示的正方形，但无需记忆，自由扫视条件要求自主进行水平扫视。将与二维扫视生成（引导扫视）相关的功能磁共振成像信号强度与工作记忆条件延迟期相关的功能磁共振成像信号强度进行比较，结果显示，在任何个体受试者中，以及在组水平上，均未发现SFC中与工作记忆相关的活动比与扫视相关的活动更强的证据，并且在五名受试者中有三名受试者中，二维扫视的活动比延迟期活动更强。这些结果未能支持如下假说：即与空间工作记忆相关的活动优先在FEF前方的SFC区域中表现出来（考特尼等人，1998年）。对工作记忆中时空信息的维持与操作进行比较，结果显示背外侧PFC中与后者相关的活动显著更强，但腹外侧PFC或SFC中并非如此。这些结果表明，SFC的延迟相关功能仅限于空间信息的维持，并且该区域不支持背外侧PFC所支持的非记忆性执行控制功能。这些结果还表明，背外侧PFC在对工作记忆中保存的信息进行操作时的优先征募适用于采用空间刺激的任务，也适用于采用言语刺激的任务（德斯波西托等人，1999年；彼得里德斯等人，1993年；波斯泰尔等人，1999年）。
