Habituation during word generation in consecutive fMRI examinations

Abstract

We assessed hemispheric language lateralization indices from ten consecutive trials in a volunteer (f; age 24) using a word generation task. Functional images were acquired by ten axial slices using an echo planar imaging sequence (1.5 Tesla Siemens Magnetom Vision; repetition time, 1.7 sec; echo time, 64 msec; flip angle, 90 degrees; field of view, 210 mm; slice thickness, 3 mm; matrix, 128 x 128; see fig. 1). fMRI regions of interest were related to the vascular territory of the middle cerecral arteries (MCA’s; see fig. 2). Additionally, averaged event related cerebral blood flow velocities in the middle arteries were measured by functional transcranial Doppler-Sonography (fTCD) using the identical word generation task 1. The fMRI language laterality index was calculated by LI = (NL NR) / (NL + NR), where NL and NR refer to the numbers of voxels activated in the left and right hemisphere, respectively. Only voxels within a region corresponding to vascular territory of the MCA s w ereconsidered.