Stern C E, Sherman S J, Kirchhoff B A, Hasselmo M E
Department of Psychology, Boston University, Massachusetts 02215, USA.
Hippocampus. 2001;11(4):337-46. doi: 10.1002/hipo.1048.
Lesions of parahippocampal structures impair performance of delayed matching tasks in nonhuman primates, suggesting a role for these structures in the maintenance of items in working memory and short-term stimulus matching. However, most human functional imaging studies have not shown medial temporal activation during working memory tasks and have primarily focused on functional magnetic resonance imaging (fMRI) signal intensity changes in the prefrontal and posterior parietal cortex. The goal of this study was to test the hypothesis that the difference between the human and nonhuman primate data results from the use of highly familiar stimuli in human working memory studies and trial-unique stimuli in nonhuman primate studies. We used fMRI to examine prefrontal and temporal lobe activation during performance of a working memory (two-back) task, using blocks of novel and highly familiar complex pictures. Performance of the working memory task with novel complex pictures resulted in greater signal change within medial temporal lobe structures than performance of the task with familiar complex pictures. In contrast, the working memory task with highly familiar stimuli resulted in greater prefrontal activation. These results are consistent without hypothesis that the medial temporal lobe is recruited for the short-term maintenance of information that has no prior representation in the brain, whereas the prefrontal cortex is important for monitoring familiar stimuli that have a high degree of interference. A second set of tasks examined stimulus matching. Subjects performed a target-matching task, during which they identified a single target presented in blocks of novel or familiar stimuli. The results provide evidence of hippocampal and parahippocampal recruitment in the target-matching task with familiar stimuli. These results are consistent with prior animal studies and suggest that prefrontal regions may be important for the monitoring and matching of familiar stimuli which have a high potential for interference, whereas medial temporal regions may become proportionally more important for matching and maintenance of novel stimuli.
海马旁结构的损伤会损害非人类灵长类动物在延迟匹配任务中的表现，这表明这些结构在工作记忆中物品的维持以及短期刺激匹配中发挥作用。然而，大多数人类功能成像研究并未显示在工作记忆任务期间内侧颞叶有激活，并且主要集中在前额叶和顶叶后部皮质的功能磁共振成像（fMRI）信号强度变化上。本研究的目的是检验这样一种假设，即人类和非人类灵长类动物数据之间的差异是由于人类工作记忆研究中使用了高度熟悉的刺激，而非人类灵长类动物研究中使用了独特刺激。我们使用fMRI来检查在执行工作记忆（二选一）任务期间前额叶和颞叶的激活情况，该任务使用了新颖和高度熟悉的复杂图片块。与使用熟悉的复杂图片执行任务相比，使用新颖复杂图片执行工作记忆任务在内侧颞叶结构内导致了更大的信号变化。相反，使用高度熟悉的刺激执行工作记忆任务导致了更大的前额叶激活。这些结果与以下假设一致，即内侧颞叶被用于对大脑中没有先前表征的信息进行短期维持，而前额叶皮质对于监测具有高度干扰性的熟悉刺激很重要。第二组任务检查了刺激匹配。受试者执行了目标匹配任务，在此期间他们识别出在新颖或熟悉刺激块中呈现的单个目标。结果提供了在使用熟悉刺激的目标匹配任务中海马和海马旁区域被激活的证据。这些结果与先前的动物研究一致，并表明前额叶区域对于监测和匹配具有高干扰潜力的熟悉刺激可能很重要，而内侧颞叶区域对于新颖刺激的匹配和维持可能会变得相对更重要。
