Functional Significance of High Baseline Activity

高基线活动的功能意义

• 批准号: 6573412
• 负责人: MARCUS E RAICHLE
• 金额: $ 28.83万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-03-01 至 2003-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6573412
• 关键词: behavioral /social science research tag; bioimaging /biomedical imaging; brain circulation; brain mapping; brain metabolism; cingulate gyrus; clinical research; cognition; emotions; frontal lobe /cortex; functional magnetic resonance imaging; human subject; motivation; neurophysiology; performance; positron emission tomography; stimulus /response

Modern functional brain imaging studies with both positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) routinely demonstrated task-induced increases as well as decreases in brain activity. The increases (usually referred to as "activations") are generally thought to reflect increases in the local cellular activity of the brain. Decreases )sometimes called "deactivations") have remained an enigma for many. Some decreases related, simply, to the manner in which the imaging experiment was conducted. Thus, activity present locally in a control state and absent in a task state to which it is compared would, quite naturally, appear as a decrease. For many, this explanation is sufficient. However, a recurring group of decreases that appear to vary little in their locations across a broad range of experimental paradigm cannot so early be explained. During the presently funded grant period of this Program Project we have determined that among this group of recurring decreases are areas where true decreases from baseline activity occur (see this Project for further details). In this project we examine their possible functional significance. We focus on two midline areas: the posterior cingulate cortex and adjacent precuneus; and, the medial and the orbital frontal cortices. They are unique in that their baseline activity greatly excee3ds other areas of the cerebral cortex suggesting the presence of a default system designed to assemble and evaluate its emotional and motivational significance. Focused attention of any sort causes an immediate reduction in the activity of this system and in the amygdala (84). This is consistent with the common observation that focused cognitive activity attenuates emotional arousal and constrains goal directed activity. However, the degree to which activity within this system is suspended during task performance presents a balance between task demands and our emotional state. This is also consistent with the common observation that our emotional and motivation state, in turn, influence cognitive performance. It is the purpose of the experiments in this project to more clearly define the relationship of cognitive to emotion and motivation as expressed through changes in the activity of this default system about its baseline level of activity.

使用正电子发射断层扫描（PET）和功能磁共振成像（fMRI）进行的现代功能性脑成像研究通常证明任务引起的大脑活动增加和减少。通常认为这种增加（通常称为“激活”）反映了大脑局部细胞活动的增加。减少（有时称为“失活”）对许多人来说仍然是一个谜。一些下降简单地与成像实验的进行方式有关。因此，在控制状态中局部存在的活动而在与之比较的任务状态中不存在的活动将很自然地表现为减少。对于许多人来说，这个解释就足够了。然而，在广泛的实验范式中，一组重复出现的下降似乎在其位置上变化不大，但不能这么早地得到解释。在本计划项目目前资助的拨款期内，我们已确定，在这组经常性减少的领域中，出现了相对于基线活动真正减少的领域（有关更多详细信息，请参阅本项目）。在这个项目中，我们研究了它们可能的功能意义。我们关注两个中线区域：后扣带皮层和邻近的楔前叶；以及内侧和眶额皮质。它们的独特之处在于，它们的基线活动大大超过了大脑皮层的其他区域，这表明存在一个旨在组装和评估其情感和动机意义的默认系统。任何形式的集中注意力都会导致该系统和杏仁核的活动立即减少（84）。这与常见的观察结果一致，即集中的认知活动会减弱情绪唤起并限制目标导向的活动。然而，在任务执行过程中该系统内的活动暂停的程度代表了任务需求和我们的情绪状态之间的平衡。这也与我们的情绪和动机状态反过来影响认知表现的普遍观察相一致。本项目实验的目的是更清楚地定义认知与情感和动机的关系，这种关系通过默认系统的活动基线水平的变化来表达。