FUNCTIONAL MRI OF TASK INDEPENDENT PROCESSING

任务引起的脑血流量减少是脑功能成像研究中经常发现的现象，但尚未得到充分解释。许多典型地表现出这种减少的大脑区域也与语义处理有关。解释这两个观察结果的一个假设是，注意力依赖的、主动的语义加工发生在有意识的休息状态，并被注意力转移到非语义任务所打断。因此，在休息或“思考”时，非语义任务会导致正常参与语义处理的区域的神经活动减少)。这项提议的具体目的是使用功能磁共振成像(FMRI)和语义处理能力的行为测量来测试该模型的主要预测。首先，该模型预测，改变注意需求、难度或非语义任务应该会在任务诱发的信号减少方面产生相关的变化，这是通过fMRI测量的。更重要的是，这些变化应该与在相同任务条件下测量的语义处理能力的降低相关。具体目的1是通过关联语义处理能力的变化和非语义任务中注意负荷的受控操作过程中fMRI信号的减少来检验这些预测。其次，该模型预测语义任务不应该导致fMRI信号减少，因为这些任务涉及的大脑区域与休息时参与语义处理的大脑区域相同。具体目标2是在注意负荷保持不变的情况下，通过测量语义加工负荷受控操作过程中fMRI信号的减少来检验这一预测。如果正确，主要假说将对语义处理的功能成像研究中不同的发现提供统一的解释，解释至少一些任务导致的“去激活”，以及广泛适用于功能成像实验设计和解释的关于静息状态大脑活动的迫切需要的信息。这些数据还可以为以异常思维内容为特征的神经精神疾病提供新的研究方法，包括精神分裂症、强迫症、情感障碍和自闭症。

Task-induced decreases in cerebral blood flow are a frequent finding in functional brain imaging research but have not been adequately explained. Many of the brain areas that typically show such decreases have also been implicated in semantic processing. One hypothesis accounting for both observations is that attention-dependent, unsolicited semantic processing occurs during conscious resting state and is interrupted by shifting of attention to non-semantic tasks. Non-semantic tasks thus produce decreases in neural activity in regions normally engaged in semantic processing during rest or "thinking"). The specific aims of this proposal are to test the main predications of this model using functional magnetic resonance imaging (fMRI) and behavioral measures of semantic processing capacity. First, the model predicts that changing the attentional demands, or difficulty, or a non-semantic task should produce correlated changes in task-induced signal decreases measured with fMRI. More importantly, these changes should be correlated with reductions in semantic processing capacity measured during the same task conditions. Specific Aim 1 is to test these predictions by correlating changes in semantic processing capacity and fMRI signal decreases during controlled manipulations of attentional load in non-semantic task. Second, the model predicts that semantic tasks should not cause fMRI signal decreases, as these tasks engage the same brain areas that are engaged in semantic processing during rest. Specific Aim 2 is to test this prediction by measuring fMRI signal decreases during controlled manipulations of semantic processing load while attentional load is held constant. If correct, the main hypotheses will provide a unifying account of disparate findings from functional imaging studies of semantic processing, an explanation for at least some task induced "deactivations," and much needed information about resting state brain activity that would be broadly applicable to the design and interpretation of functional imaging experiments. These data could also provide novel research approaches to neuropsychiatric conditions characterized by abnormal thought content, including schizophrenia, obsessive compulsive disorder, affective disorder, and autism.