Konishi Seiki, Jimura Koji, Asari Tomoki, Miyashita Yasushi
Department of Physiology, The University of Tokyo School of Medicine, Tokyo 113, Japan.
J Neurosci. 2003 Aug 27;23(21):7776-82. doi: 10.1523/JNEUROSCI.23-21-07776.2003.
The prefrontal cortex implements a set-shifting function that includes inhibition of a previously acquired cognitive set. The impairment of the inhibitory function results in perseverative behavior that forms one characteristic feature of frontal lobe dysfunction. Previous neuroimaging studies have revealed inhibitory mechanisms in the inferior prefrontal cortex. The present functional magnetic resonance imaging study devised "dual-match" stimuli in a set-shifting paradigm that allowed us to temporally isolate the inhibitory processes recruited during exposure to a previously acquired set. Transient activation time-locked to the isolated inhibition was revealed in the left middle frontal gyrus near the superior frontal sulcus. In a control experiment conducted after subjects had been informed and made aware of the exposure, however, the superior prefrontal activation disappeared, and prominent activation was revealed in a set of brain regions that included the left posterior inferior frontal sulcus. These double dissociation results indicate inhibitory mechanisms in the superior prefrontal cortex, alternative to the inferior prefrontal ones, that are activated depending on the subjects' strategy for inhibition of cognitive set.
前额叶皮层执行一种定势转换功能，其中包括对先前习得的认知定势的抑制。抑制功能受损会导致持续性行为，这是额叶功能障碍的一个特征。先前的神经影像学研究已经揭示了前额叶下部皮层的抑制机制。本功能磁共振成像研究在定势转换范式中设计了“双重匹配”刺激，使我们能够在时间上分离出在接触先前习得的定势时所招募的抑制过程。在靠近额上沟的左侧额中回中发现了与孤立抑制时间锁定的瞬时激活。然而，在告知受试者并使其意识到这种接触后进行的对照实验中，前额叶上部的激活消失了，并且在包括左侧额下后沟在内的一组脑区中发现了明显的激活。这些双重解离结果表明，前额叶上部皮层存在与前额叶下部皮层不同的抑制机制，其激活取决于受试者抑制认知定势的策略。
