Functional Significance of High Baseline Activity

现代的功能性脑成像研究，包括正电子发射断层扫描（PET）和功能性磁共振成像（fMRI），常规地显示了任务引起的大脑活动的增加和减少。这种增加（通常称为“激活”）通常被认为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。有些下降与进行成像实验的方式有关。因此，在控制状态中局部存在的活动和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。对许多人来说，这个解释已经足够了。然而，一组反复出现的减少，似乎在他们的位置变化不大，在广泛的实验范式不能这么早解释。在本计划项目目前资助的赠款期间，我们已经确定，在这组经常性减少的领域中，基线活动发生了真正的减少（详见本项目）。在这个项目中，我们研究它们可能的功能意义。我们专注于两个中线区域：后扣带皮层和相邻的楔前叶;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，这表明存在一个默认系统，旨在收集和评估其情感和动机的重要性。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）。这与集中的认知活动减弱情绪唤醒并限制目标导向活动的常见观察结果一致。然而，在任务执行过程中，这个系统中的活动被暂停的程度在任务需求和我们的情绪状态之间呈现出平衡。这也与我们的情绪和动机状态反过来影响认知表现的常见观察一致。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，这些关系通过该默认系统的活动相对于其基线活动水平的变化来表达。

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.