Abstract:The aim of this work is to characterize quantitatively the performance of a body of techniques in the frequency domain for the estimation of cortical connectivity from high-resolution EEG recordings in different operative conditions commonly encountered in practice. Connectivity pattern estimators investigated are the Directed Transfer Function (DTF), its modification known as direct DTF (dDTF) and the Partial Directed Coherence (PDC). Predefined patterns of cortical connectivity were simulated and then retrieved by the application of the DTF, dDTF, and PDC methods. Signal-to-noise ratio (SNR) and length (LENGTH) of EEG epochs were studied as factors affecting the reconstruction of the imposed connectivity patterns. Reconstruction quality and error rate in estimated connectivity patterns were evaluated by means of some indexes of quality for the reconstructed connectivity pattern. The error functions were statistically analyzed with analysis of variance (ANOVA). The whole methodology was then applied to high-resolution EEG data recorded during the well-known Stroop paradigm. Simulations indicated that all three methods correctly estimated the simulated connectivity patterns under reasonable conditions. However, performance of the methods differed somewhat as a function of SNR and LENGTH factors. The methods were generally equivalent when applied to the Stroop data. In general, the amount of available EEG affected the accuracy of connectivity pattern estimations. Analysis of 27 s of nonconsecutive recordings with an SNR of 3 or more ensured that the connectivity pattern could be accurately recovered with an error below 7% for the PDC and 5% for the DTF. In conclusion, functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in most EEG recordings by combining high-resolution EEG techniques, linear inverse estimation of the cortical activity, and frequency domain multivariate methods such as PDC, DTF, and dDTF. Hum Brain Mapp 28:143-157, 2007.

P rognosis of functional outcome after ischemic stroke is influenced by a variety of factors already assessable in the acute phase and within the first days after symptom onset. In clinical trials, stroke outcome is most commonly rated by the modified Rankin Scale (mRS) 1 because of the validity and rapid application of this rating scale and its ability to discriminate clinically relevant levels of disability and recovery.2-4 Brain imaging in the early phase after stroke onset provides valuable information related to individual functional recovery. 5,6 In particular, structural MRI identifies injured brain regions and allows for assessment of extent and location, both known to influence and predict functional outcome measured by the mRS.3 However, infarct volume from early MRI correlates only moderately with the mRS at later time points, 7,8 indicating that additional factors, such as lesion location, influence functional outcome. It is therefore of major interest to elucidate the relationship between early lesion patterns and functional impairment in the later course of stroke.Clinical impact of lesion locations can be inferred from voxel-based lesion symptom mapping (VLSM). This statistical method examines effects of brain lesions on behavioral scores on a voxel-by-voxel base. Therefore, a statistical test is conducted for each voxel to detect differences in a behavioral score based on the presence or absence of injury.9 VLSM produces statistical results that map structural lesions to a behavioral scale. In patients with chronic stroke, it has been Background and Purpose-In the early days after ischemic stroke, information on structural brain damage from MRI supports prognosis of functional outcome. It is rated widely by the modified Rankin Scale that correlates only moderately with lesion volume. We therefore aimed to elucidate the influence of lesion location from early MRI (days 2-3) on functional outcome after 1 month using voxel-based lesion symptom mapping. Methods-We analyzed clinical and MRI data of patients from a prospective European multicenter stroke imaging study (I-KNOW). Lesions were delineated on fluid-attenuated inversion recovery images on days 2 to 3 after stroke onset. We generated statistic maps of lesion contribution related to clinical outcome (modified Rankin Scale) after 1 month using voxel-based lesion symptom mapping. Results-Lesion maps of 101 patients with middle cerebral artery infarctions were included for analysis (right-sided stroke, 47%). Mean age was 67 years, median admission National Institutes of Health Stroke Scale was 11. Mean infarct volumes were comparable between both sides (left, 37.5 mL; right, 43.7 mL). Voxel-based lesion symptom mapping revealed areas with high influence on higher modified Rankin Scale in regions involving the corona radiata, internal capsule, and insula. In addition, asymmetrically distributed impact patterns were found involving the right inferior temporal gyrus and left superior temporal gyrus. Conclusions-In this group of patients with strok...