Sergent J, Zuck E, Lévesque M, MacDonald B
Montreal Neurological Institute, McGill University, Quebec, Canada.
Cereb Cortex. 1992 Jan-Feb;2(1):68-80. doi: 10.1093/cercor/2.1.68.
The study of functional-anatomical correlations of higher-order cognitive processing has benefited from recent advances in brain imaging techniques such as positron emission tomography (PET) measurements of regional cerebral blood flow (CBF). Comparisons of CBF changes by paired image subtraction provide the opportunity to isolate cerebral areas participating in the realization of the processes that differentiate two tasks. However, the subtraction method is based on assumptions that are not entirely compatible with cerebral cognitive processing, and the derived pattern of activation specifically associated with the processes that differentiate two tasks is relative to the activation associated with the subtracted task and may therefore vary as a function of the processes actually performed in this subtracted task. To examine the implications of this procedure, a PET study with the 15O water bolus technique was carried out on normal adults. Subjects performed three tasks that made nonoverlapping cognitive processing demands: a semantic categorization of visual objects, a spatial discrimination of visually presented letters, and a phonological decision on visually presented single letters. Each task produced distinct patterns of activation consistent with evidence from neurological patients, specifically in the left occipital cortex in the semantic categorization of objects, in the parietal cortex of both hemispheres in the letter-spatial task, and in the left frontal and superior temporal cortex in the letter-sound task. However, the comparisons between the two letter tasks did not result in the expected CBF changes even though these two tasks make distinct processing requirements and are dissociable by brain injury. In addition, the phonological task resulted in activation of areas of the frontal cortex that earlier PET studies had identified as participating in semantic operations, whereas letters have no semantic property. These results suggest that the interpretation of patterns of activation is confronted with difficulties due to the automatic, and uncontrolled, processing of verbal stimuli that raises the threshold for significant CBF changes between two conditions that use the same stimuli but different task demands.
高阶认知加工功能 - 解剖学相关性的研究受益于脑成像技术的最新进展，如正电子发射断层扫描（PET）测量局部脑血流量（CBF）。通过配对图像相减比较CBF变化，为分离参与区分两项任务的过程的脑区提供了机会。然而，相减方法基于的假设与脑认知加工并不完全兼容，并且与区分两项任务的过程具体相关的激活模式相对于与相减任务相关的激活而言，因此可能会因在该相减任务中实际执行的过程而变化。为了研究该程序的影响，对正常成年人进行了一项使用(^{15}O)水团注技术的PET研究。受试者执行了三项提出不重叠认知加工要求的任务：视觉对象的语义分类、视觉呈现字母的空间辨别以及视觉呈现单个字母的语音判定。每项任务都产生了与神经学患者证据一致的独特激活模式，具体而言，在对象语义分类中左枕叶皮质激活，在字母空间任务中双侧顶叶皮质激活，在字母声音任务中左额叶和颞上皮质激活。然而，尽管这两项字母任务提出了不同的加工要求并且可通过脑损伤区分，但两项字母任务之间的比较并未产生预期的CBF变化。此外，语音任务导致额叶皮质区域激活，而早期PET研究已确定这些区域参与语义操作，而字母并无语义属性。这些结果表明，由于言语刺激的自动且不受控制的加工提高了使用相同刺激但任务要求不同的两种条件之间显著CBF变化的阈值，激活模式的解释面临困难。
