[Neurofunctional MRI imaging of higher cognitive performance of the human brain]

Functional magnetic resonance imaging (fMRI) offers a powerful experimental tool for mapping activated cortical regions in man. Thereby, the paramagnetic deoxyhemoglobin in the red blood cells acts as an endogenous susceptibility contrast agent, which allows the noninvasive detection of stimulus-induced transient changes in regional cerebral blood flow and volume. Fifteen normal subjects were examined on a conventional 1.5-T MR system to visualize cortical activation during the performance of high-level cognitive tasks. A computer-controlled videoprojector was employed to present psychometrically optimized activation paradigms. Reaction times and error rates of the volunteers were acquired online during stimulus presentation. The time course of cortical activation was measured in a series of strongly T2*-weighted gradient-echo images from three or four adjacent slices. For anatomical correlation, picture elements showing a stimulus-related significant signal increase were color-coded and superimposed on T1-weighted spin-echo images. Analysis of the fMRI data revealed a subtle (range 2-5%), but statistically significant (P < 0.05) increase in signal intensity during the periods of induced cortical activation. Judgment of semantic relatedness of word pairs, for example, activated selectively cortical areas in left frontal and left temporal brain regions. The strength of cortex activation in the semantic task decreased significantly in the course of stimulus presentation and was paralleled by a decrease in the corresponding reaction times. With its move into the area of cognitive neuroscience, fMRI calls both for the careful design of activation schemes and for the acquisition of behavioral data. For example, brain regions involved in language processing could only be identified clearly when psychometrically matched activation paradigms were employed. The reaction time data correlated well with selective learning and thus helped to facilitate interpretation of the fMRI data sets.