FUNCTIONAL MRI OF TASK INDEPENDENT PROCESSING

任务诱发的脑血流量减少是脑功能成像研究中的常见结果，但尚未得到充分解释。许多通常表现出这种下降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，主动的语义处理发生在有意识的休息状态，并被打断的注意力转移到非语义任务。因此，非语义任务会导致休息或“思考”期间通常参与语义处理的区域的神经活动减少。这项建议的具体目的是测试这个模型的主要预测使用功能性磁共振成像（fMRI）和语义处理能力的行为措施。首先，该模型预测，改变注意力的需求，或难度，或非语义任务应该产生相关的变化，在任务引起的信号减少与功能磁共振成像测量。更重要的是，这些变化应该与在相同的任务条件下测量的语义处理能力的减少相关。具体目标1是通过将语义加工能力的变化与非语义任务中注意负荷的控制操作过程中fMRI信号的下降相关联来验证这些预测。其次，该模型预测语义任务不应该导致fMRI信号下降，因为这些任务涉及与休息时从事语义处理的相同大脑区域。具体目标2是通过测量语义处理负荷的控制操作过程中，而注意力负荷保持不变的功能磁共振成像信号的减少来测试这一预测。如果正确的话，主要的假设将提供一个统一的帐户不同的结果从功能成像研究的语义处理，解释至少有一些任务引起的“失活”，以及急需的信息休息状态下的大脑活动，将广泛适用于设计和解释功能成像实验。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.