FUNCTIONAL MRI OF TASK INDEPENDENT PROCESSING

任务诱发的脑血流量减少是功能性脑成像研究中经常发现的现象，但尚未得到充分解释。许多通常表现出这种减少的大脑区域也与语义处理有关。一种解释这两种观察结果的假设是，注意力依赖的、未经请求的语义处理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，非语义任务会导致通常参与语义处理的区域的神经活动减少。本建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，改变注意力需求、难度或非语义任务应该会产生fMRI测量的任务诱发信号减少的相关变化。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减少相关。具体目的1是通过在非语义任务的注意负荷控制操作中语义处理能力的变化与fMRI信号减少的相关性来验证这些预测。其次，该模型预测语义任务不会导致fMRI信号减少，因为这些任务涉及的大脑区域与休息时从事语义处理的大脑区域相同。具体目标2是通过测量在注意负荷保持不变的情况下语义处理负荷的控制操作过程中fMRI信号的减少来验证这一预测。如果正确的话，主要假设将为语义处理的功能成像研究的不同发现提供一个统一的解释，至少解释一些任务引起的“失活”，以及关于静息状态大脑活动的急需信息，这些信息将广泛适用于功能成像实验的设计和解释。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.