The development of high-resolution neuroimaging and multielectrode electrophysiological recording provides neuroscientists with huge amounts of multivariate data. The complexity of the data creates a need for statistical summary, but the local averaging standardly applied to this end may obscure the effects of greatest neuroscientific interest. In neuroimaging, for example, brain mapping analysis has focused on the discovery of activation, i.e., of extended brain regions whose average activity changes across experimental conditions. Here we propose to ask a more general question of the data: Where in the brain does the activity pattern contain information about the experimental condition? To address this question, we propose scanning the imaged volume with a ''searchlight,'' whose contents are analyzed multivariately at each location in the brain.neuroimaging ͉ functional magnetic resonance imaging ͉ statistical analysis F unctional brain mapping has evolved from the idea that the brain consists of functionally specialized macroscopic regions. In early neuroimaging experiments using positron emission tomography, brain activity was measured at a spatial resolution in the centimeter range. At this resolution, the volume elements (voxels) were similar in size to the putative functional regions, so only the spatial-average activity of a region could be studied. In the classical approach to functional brain mapping, therefore, the experiment is designed to activate a functional region as a whole. The region is then localized by computing an activation statistic for each location of the imaging volume and thresholding the resulting statistical map. We refer to this approach as activation-based.With the advent of functional magnetic resonance imaging (fMRI), spatial resolution increased. Standard functional measurements were performed with voxel widths of Ϸ4 mm in each dimension. Although a typical functional region at this resolution is covered by multiple voxels, standard fMRI analysis to this day has remained true to the activation-based approach, in which a region is assumed to become active as a whole. This approach manifests itself in the widespread investigation of the spatially averaged activity for regions of interest. Event-related average time courses and bar graphs depicting the activity across conditions, for example, reflect a region's spatially averaged activity.The assumption that functional regions extended across multiple voxels will become activated as a whole also plays a key role in statistical inference at the level of whole maps in several established methods, including the widespread statistical parametric mapping (refs. 1-3; see also ref. 4). The extendedactivations assumption motivates the spatial smoothing of the data, which is standardly performed. Spatial smoothing accentuates extended activations by removing the ''salt-and-pepper'' fine structure of the activity patterns, which is treated as noise. As a positive side effect, the resulting reduction of the data's spatial complexity alleviat...

We propose Granger causality mapping (GCM) as an approach to explore directed influences between neuronal populations (effective connectivity) in fMRI data. The method does not rely on a priori specification of a model that contains pre-selected regions and connections between them. This distinguishes it from other fMRI effective connectivity approaches that aim at testing or contrasting specific hypotheses about neuronal interactions. Instead, GCM relies on the concept of Granger causality to define the existence and direction of influence from information in the data. Temporal precedence information is exploited to compute Granger causality maps that identify voxels that are sources or targets of directed influence for any selected region-of-interest. We investigated the method by simulations and by application to fMRI data of a complex visuomotor task. The presented exploratory approach of mapping influences between a region of interest and the rest of the brain can form a useful complement to existing models of effective connectivity. D 2004 Elsevier Inc. All rights reserved.

The Functional Image Analysis Contest (FIAC) 2005 dataset was analyzed using BrainVoyager QX. First, we performed a standard analysis of the functional and anatomical data that includes preprocessing, spatial normalization into Talairach space, hypothesis-driven statistics (one- and two-factorial, single-subject and group-level random effects, General Linear Model [GLM]) of the block- and event-related paradigms. Strong sentence and weak speaker group-level effects were detected in temporal and frontal regions. Following this standard analysis, we performed single-subject and group-level (Talairach-based) Independent Component Analysis (ICA) that highlights the presence of functionally connected clusters in temporal and frontal regions for sentence processing, besides revealing other networks related to auditory stimulation or to the default state of the brain. Finally, we applied a high-resolution cortical alignment method to improve the spatial correspondence across brains and re-run the random effects group GLM as well as the group-level ICA in this space. Using spatially and temporally unsmoothed data, this cortex-based analysis revealed comparable results but with a set of spatially more confined group clusters and more differential group region of interest time courses.

Signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths. The variation in B 1 magnitude was nearly twofold higher at 7T than at 4T (ϳ42% compared to ϳ23%). The power required for a 90°pulse in the center of the head at 7T was approximately twice that at 4T. The SNR averaged over the brain was at least 1.6 times higher at 7T compared to 4T. These experimental results were consistent with calculations performed using a human head model and Max In the last decade, MRI studies conducted at 4T have demonstrated the utility of high magnetic fields in functional and anatomical imaging of the human brain and for spectroscopy studies in the brain and the human body (1-7). These accomplishments and the continued successes at magnetic fields up to 9.4T with animal models have paved the way for the exploration of magnetic fields of higher than 4T for human brain studies (8 -12). Consequently, recent efforts have been undertaken to establish 8T and 7T systems, the latter in our laboratory (13)(14)(15). Now with an operational 7T system, the signal-to-noise ratio (SNR), RF field (B 1 ), and RF power requirement at 7T were compared to the same parameters at 4T. MATERIALS AND METHODSIn this 7T vs. 4T comparison study, we used the same size coils, the same model consoles, identical acquisition parameters, and the same volunteers for six carefully reproduced experiments at each field strength. Hardware SystemsThis experiment was performed on Varian Unity Inova consoles interfaced to 90 cm bore Oxford 4T and Magnex 7T magnets. The noise figures of the two systems were the same, measuring 1.3 dB. Siemens body gradients (65 cm i.d.) and Magnex head gradients (38 cm i.d.) were used in the 4T and 7T systems, respectively. Coils

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