Aguirre Geoffrey Karl
Department of Neurology, University of Pennsylvania, 3 West Gates, 3400 Spruce Street, Philadelphia, PA 19104, USA.
Neuroimage. 2007 May 1;35(4):1480-94. doi: 10.1016/j.neuroimage.2007.02.005. Epub 2007 Feb 15.
This paper describes continuous carry-over fMRI experiments. In these studies, stimuli are presented in an unbroken, sequential manner, and can be used to estimate simultaneously the mean difference in neural activity between stimuli as well as the effect of one stimulus upon another (carry-over effects). Neural adaptation, which has been the basis of many recent fMRI studies, is shown to be a specific form of carry-over effect. With this approach, the adapting effects of stimuli may be studied in a continuous sequence, as opposed to within isolated pairs or blocks. Additionally, the average, direct effect of a stimulus upon neural response can form the basis of a simultaneously obtained distributed pattern analysis, allowing comparison of neural population coding on focal (within voxel) and distributed (across voxel) spatial scales. These studies are ideally conducted with serially balanced sequences, in which every stimulus precedes and follows every other stimulus. While m-sequences can provide this stimulus order, the type 1 index 1 sequence of Finney and Outhwaite may be used in fMRI studies for those experimental designs for which an m-sequence solution does not exist. Continuous carry-over designs with serially balanced sequences are argued to be particularly well suited to the characterization of "similarity spaces," in which the perceptual similarity of stimuli is related to the structure of neural representation both within and across voxels. These concepts are illustrated with a worked example involving the neural representation of color. It is shown that data from a single scanning session are sufficient to detect direct and carry-over effects, as well as demonstrate the correspondence of the similarity structure of distributed patterns of neural firing and the perceptual similarity of a set of colors.
本文描述了连续遗留功能磁共振成像实验。在这些研究中，刺激以不间断的连续方式呈现，可用于同时估计刺激之间神经活动的平均差异以及一个刺激对另一个刺激的影响（遗留效应）。神经适应性是许多近期功能磁共振成像研究的基础，它被证明是遗留效应的一种特殊形式。通过这种方法，可以在连续序列中研究刺激的适应性效应，而不是在孤立的刺激对或刺激块中进行研究。此外，刺激对神经反应的平均直接效应可构成同时获得的分布式模式分析的基础，从而能够在焦点（体素内）和分布式（跨体素）空间尺度上比较神经群体编码。这些研究理想情况下采用序列平衡序列进行，即每个刺激在其他每个刺激之前和之后都出现。虽然m序列可以提供这种刺激顺序，但对于不存在m序列解决方案的实验设计，芬尼和奥特韦特的1型索引1序列可用于功能磁共振成像研究。具有序列平衡序列的连续遗留设计被认为特别适合于表征“相似性空间”，其中刺激的感知相似性与体素内和跨体素的神经表征结构相关。通过一个涉及颜色神经表征的实例对这些概念进行了说明。结果表明，单次扫描会话的数据足以检测直接和遗留效应，以及证明神经放电分布式模式的相似性结构与一组颜色的感知相似性之间的对应关系。
