Functional connectivity in the thalamus and hippocampus studied with functional MR imaging

BACKGROUND AND PURPOSE: With functional connectivity functional MR imaging, covariance in signal intensity has been shown in functionally related regi ons of brain in participants instructed to perform no cognitive task. These changes are thought to represent synchronous fluctuations in blood flow, w hich imply neuronal connections between the regions. The purpose of this st udy was to map functional connectivity in subcortical nuclei with functiona l connectivity functional MR imaging. METHODS: Imaging data were acquired with an echo-planar sequence from six v olunteers who performed no specific cognitive task. For functional connecti vity functional MR imaging, a "seed" voxel or group of voxels was selected from the resting data set in the thalamus or in the hippocampus. Control vo xels in gray matter presumed not to be eloquent cortex were also chosen. Th e correlation coefficient of the seed voxels and the control voxels with ev ery other vox-el in the resting data set was calculated. The voxels with co rrelation coefficients greater than or equal to 0.5 were mapped onto anatom ic images for the functional connectivity functional MR images. The anatomi c location of these voxels was determined by conventional parcellation meth ods. RESULTS: For each participant, functional connectivity functional MR imagin g maps based on four seed voxels in the thalamus or hippocampus showed clus ters of voxels in the ipsilateral and contralateral thalamus or hippocampus . For control voxels, few voxels in the hippocampus or thalamus showed sign ificant correlation. Significantly more pixels in the ipsilateral hippocamp us correlated with the seed voxel than in the contralateral hippocampus. Th e differences between numbers of functionally connected voxels in ipsilater al thalamus and those in contralateral thalamus were not significant. CONCLUSIONS: The thalamus and hippocampus show functional connectivity, pre sumably representing synchronous changes in blood flow.